Download - persistence and transformation of carbosulfan in laterite and coastal alluvium soils of kerala
PERSISTENCE AND TRANSFORMATION OF CARBOSULFAN
IN LATERITE AND COASTAL ALLUVIUM SOILS OF KERALA AND
ITS EFFECT ON SOIL ORGANISMS
DHANYA. M . S
(2014 – 11 - 152)
DEPARTMENT OF SOIL SCIENCE AND AGRICULTURAL CHEMISTRY
COLLEGE OF AGRICULTURE
VELLAYANI, THIRUVANANTHAPURAM-695 522
KERALA, INDIA
2016
PERSISTENCE AND TRANSFORMATION OF CARBOSULFAN
IN LATERITE AND COASTAL ALLUVIUM SOILS OF KERALA
AND ITS EFFECT ON SOIL ORGANISMS
by DHANYA. M. S
(2014-11-152)
THESIS
Submitted in partial fulfilment of the
requirements for the degree of
MASTER OF SCIENCE IN AGRICULTURE
Faculty of Agriculture
Kerala Agricultural University
DEPARTMENT OF SOIL SCIENCE AND AGRICULTURAL CHEMISTRY
COLLEGE OF AGRICULTURE
VELLAYANI, THIRUVANANTHAPURAM-695 522
KERALA, INDIA
2016
DECLARATION
I, hereby declare that this thesis entitled “PERSISTENCE AND TRANSFORMATION OF
CARBOSULFAN IN LATERITE AND COASTAL ALLUVIUM SOILS OF KERALA
AND ITS EFFECT ON SOIL ORGANISMS” is a bonafide record of research work done by
me during the course of research and the thesis has not previously formed the basis for the award
to me of any degree, diploma, associateship, fellowship or other similar title, of any other
University or Society.
Vellayani, Dhanya. M. S
06-09-2016 (2014 - 11-152)
ii
CERTIFICATE
Certified that this thesis entitled “PERSISTENCE AND TRANSFORMATION OF
CARBOSULFAN IN LATERITE AND COASTAL ALLUVIUM SOILS OF KERALA
AND ITS EFFECT ON SOIL ORGANISMS” is a record of research work done
independently by Ms. Dhanya M. S under my guidance and supervision and that it has not
previously formed the basis for the award of any degree, diploma, fellowship or associateship to
her.
Vellayani, Dr. Thomas George
-09-2016 (Major Advisor, Advisory Committee)
Professor (Soil Science & Agrl. Chemistry)
All India Network Project (AINP) on Pesticide Residues
College of Agriculture, Vellayani
iii
CERTIFICATE
We, the undersigned members of the advisory committee of Ms. Dhanya. M. S, a candidate for
the degree of Master of Science in Agriculture with major in Soil Science and Agricultural
Chemistry, agree that this thesis entitled “PERSISTENCE AND TRANSFORMATION OF
CARBOSULFAN IN LATERITE AND COASTAL ALLUVIUM SOILS OF KERALA
AND ITS EFFECT ON SOIL ORGANISMS” may be submitted by Ms. Dhanya. M. S., in
partial fulfillment of the requirement for the degree.
Dr. Thomas George Dr. Sumam George
(Chairman, Advisory Committee) (Member, Advisory Committee) Professor
(SS&AC) Professor and Head Dept. of Soil Science & Agrl. Chemistry Dept. of Soil Science & Agrl. Chemistry AINP on Pesticide Residues College of Agriculture, Vellayani
College of Agriculture, Vellayani
Dr. K. C. Manorama Thampatti Dr. Thomas Biju Mathew (Member, Advisory Committee) (Member, Advisory Committee)
Professor Professor Dept. of Soil Science & Agrl. Chemistry (Department of Agricultural Entomology)
College of Agriculture, Vellayani Pesticide Residue Research and Analytical Laboratory, (PRRAL) College of Agriculture, Vellayani
EXTERNAL EXAMINER
(Name and Address)
iv
ACKNOWLEDGEMENT
With utmost reverence and deep sense of admiration, I express my heartfelt gratitude and
indebtedness to God almighty for the help rendered during my M.Sc. programme and giving me
the courage and strength to pursue this endeavor to completion.
I express my exuberant pleasure to express my deep sense of gratitude to
Dr. Thomas George, Professor, Department of Soil Science and Agricultural Chemistry, AINP
on Pesticide Residues and chairman of my Advisory committee for his valuable guidance,
constant encouragement, timely advice, overwhelming support and care rendered during the
research period without which this piece of work would not have been materialized. I proudly
acknowledge that this manuscript has gained its completeness under the kind supervision and
inspiration of my guide and he has been a valuable support for both academic and personal
level, for which I am extremely grateful.
I am very much grateful to the timely support, sincere efforts, valuable suggestions
motherly affection and constant encouragement from the beginning till the end offered by Dr.
Sumam George, Professor and Head, Department of Soil Science and Agricultural Chemistry
which played a major role for the successful completion of this work.
I am deeply indebted to Dr. K. C. Manorama Thampatti, Professor Department of Soil
Science and Agricultural Chemistry for her invaluable guidance, inspiring support,
encouragement during the course of my investigation.
I feel immense pleasure to avail the opportunity to convey my heartfelt thanks to Dr.
Thomas Biju Mathew, Professor, Department of Agricultural Entomology, Pesticide Residue
Research and Analytical Laboratory for providing necessary facility, selfless help and
encouragement during my M. Sc. programme.
I owe my immense gratitude with pleasure to Dr. N. Saifudeen, Professor and Head
(Retired), Department of Soil Science and Agricultural Chemistry, Dr. Sumam Susan
Vargheese, Professor and Head (Retired), Department of Soil Science and Agricultural
v
Chemistry ex- members of my advisory committee for the encouragement and constructive
criticisms rendered during the course of my work.
I wish to record my special thanks to the generous and selfless help of Dr. S. Naseema
Beevi, Professor (Retired), Department of Agricultural Entomology rendered to me during the
course of my work.
Words are inadequate to express my special and sincere thanks to Dr. Ushakumari
Professor, Department of Soil Science and Agricultural Chemistry, Dr. Ambily Paul, Assistant
Professor, Department of Agriculture Entomology and Dr. K. S Premila, Professor, Department
of Agricultural Entomology for their moral support, love, care, motivation, suggestion and
affection rendered throughout the study.
My study will not be a complete one if I forget to show my gratitude to my teachers in
Department of Soil Science and Agricultural Chemistry Dr. P. B Usha, Dr. Usha Mathew, Dr.
Sudharmai Devi, Dr. B. Aparna, Dr. Gladis, Dr. Biju Joseph, Dr. B. Rani and Dr. Sam T
Kurumthottical, for their friendly approach, well wishes and constant encouragement during
the study.
I am equally grateful to Dr. Vijayaraghava Kumar, Professor and Head, Department of
Agricultural Statistics, for his valuable guidance in statistical analysis and interpretation.
I wish to express my sincere gratitude to Dr. Komala Amma, Professor (Retired)
Department of Soil Science and Agricultural Chemistry and Dr. S. Shehana, Professor
(Retired), Department of Soil Science and Agricultural Chemistry for their valuable support and
wishes during my study.
I wish to express my sincere and special thanks to Visal chettan and Pratheesh chettan
for their help, support, encouragement and brotherly affection which helped me a lot for
completing this thesis work
This thesis would not have been completed without the support of Preetha Chechi,
Emile Chechi, Sreekkutty Chechi, Shyju Chettan, Sreelal chettan, Vishnu, Neethu Chechi,
vi
Mithra Chechi, Salmon Chettan, George Chettan, Pradeep chettan, Rejith Chettan, , Sabari,
Binoy Chettan, Anil Chettan, Prathibha Chechi, Priya Chechi, Surya Chechi, Reshmi Chechi,
Deepa Chechi, Dhanya Chechi, Shyja Chechi and Swapna Chechi. I gratefully venerate the
un-sizable help from each of them.
I wish to express my special thanks to Shoney Chechi, Dathan Sir and Visweswaran Sir
for their timely advice, encouragement and wishes during my research work .
I would like to express my thanks to my seniors, Sreya Chechi, Anila chechi, Sreeja
Chechi, Sai Chettan, Sangeetha Chechi, Emile Chechi, Meera Chechi, Naveen Sir, Priya
Chechi and Faseela Chechi for their support and motivation during my course.
I owe my gratitude to the non teaching staff of Department of Soil Science and
Agricultural Chemistry, Shiny Chechi, Biju Chettan, Geethu Chechi, Soumya Chechi, Priya
Chechi, Vijayakumar Chettan, Aneesh Chettan, Anil Chettan and Rajesh Chettan for their
timely support during my M. Sc. Programme.
I wish to express my whole hearted thanks to my juniors, Dhanesh, Dhanya, Ragi,
Anjana, Aswathi and Usha for their help, support and care.
Words fail to express my sincere thanks to my dear friends Reshma, Arya, Jaya, Nikitha,
Amala, Anusree, Anju K K, Aaruni, Thamil, Shewtha, Jaffin, Molu, Leena, Libi, Dhanya P,
Nimisha, Rami, Reshma S, Shani, Suvarna, Faseela, Jobin, Thasni, Janish and Amju for
their affection and emotional support during these days without which my work wouldn’t have
been completed.
I sincerely acknowledge the Kerala Agricultural University for providing the necessary
facilities and support during my course.
Diction is not at all enough to express my feelings towards my family, especially my
beloved Achan, Amma, Ammomma, Jayan annan , Rakesh annan, Lekshmi Chechi, and my
Appoos, who supported, guided and encouraged me always, without their prayers and blessings
this work would not have been completed.
Again I wish to thank all who helped me directly or indirectly for the completion of this work
vii
CONTENTS
Sl. No. Particulars Page No.
1. INTRODUCTION 1-3
2. REVIEW OF LITERATURE 4-20
3. MATERIALS AND METHODS 21-35
4. RESULTS 36-85
5. DISCUSSION 86-100
6. SUMMARY 101-106
7. REFERENCES 107-121
ABSTRACT 122-125
APPENDIX I-V
viii
LIST OF TABLES
Table No
Title Page No
1. Environmental factors influencing the pesticide persistence 1
2. Analytical methods followed to test the physico - chemical
parameters in soil 9
3. The glass wares, equipments, and reagents used for residue
analysis
22
4. Details of Certified Reference Materials (CRMs) used for
the preparation of pesticide mixture 24
5. Multiple- reaction monitoring (MRM) and Liquid
Chromatograph (LC) parameters for carbosulfan and its
metabolites.
25
6. Physico-chemical properties of laterite soil 28
7. Physico-chemical properties of coastal alluvial soil 37
8. Mean recovery of carbosulfan and its metabolites when
spiked at 0.05 mg kg-1 level in laterite soil 38
9. Mean recovery of carbosulfan and its metabolites when
spiked at 0.25 mg kg-1 level in laterite soil 40
10. Mean recovery of carbosulfan and its metabolites when
spiked at 0.50 mg kg-1 level in laterite soil 40
11 Mean recovery of carbosulfan and its metabolites when
spiked at 0.05 mg kg-1 level in coastal alluvial soil 40
12. Mean recovery of carbosulfan and its metabolites when
spiked at 0.25 mg kg-1 level in coastal alluvial soil 41
13 Mean recovery of carbosulfan and its metabolites when
spiked at 0.50 mg kg-1 level in coastal alluvial soil 41
14 Migration of carbosulfan in laterite soil column when
loaded at100 µg level 41
ix
15
Migration of carbofuran formed in laterite soil column
when loaded with 100 µg carbosulfan 44
16 Migration of carbosulfan in laterite soil column when
loaded at 150 µg level 45
17 Migration of carbofuran formed in laterite soil column
when loaded with 150 µg carbosulfan 45
18 Migration of carbosulfan in laterite soil column when
loaded at 200 µg level 46
19 Migration of carbofuran formed in laterite soil column
when loaded with 200 µg carbosulfan 46
20 Migration of carbosulfan in the coastal alluvial soil column
when loaded at 100 µg level 49
21 Migration of carbofuran formed in coastal alluvial soil column when loaded with 100 µg carbosulfan
49
22 Migration of carbosulfan in the coastal alluvial soil column when loaded at 150 µg level
50
23 Migration of carbofuran formed in coastal alluvial soil
column when loaded with 150 µg carbosulfan 50
24 Migration of carbosulfan in the coastal alluvial soil column
when loaded at 200 µg level 51
25 Migration of carbofuran formed in coastal alluvial soil
column when loaded with 200 µg carbosulfan 51
26 Dissipation of carbosulfan 25 EC in laterite soil under laboratory and cropped conditions
54
27 Dissipation of carbosulfan 25 EC in coastal alluvial soil
under laboratory and cropped conditions 56
28 Dissipation of carbosulfan granules in laterite soil under
laboratory and cropped conditions 58
29 Dissipation of carbosulfan granules in coastal alluvial soil under laboratory and cropped conditions
59
30 Overall dissipation of carbosulfan as influenced by soil,
formulation, crop and treatment levels 61
31 Dissipation of carbosulfan as influenced by treatment levels
63
x
32 Dissipation of carbosulfan as influenced by interaction of soil, formulations and conditions
64
33 Dissipation of carbosulfan as influenced by soil,
formulations and treatment levels 66
34 Dissipation of carbosulfan as influenced by interaction of crop and treatment levels
67
35 Metabolites of carbosulfan 25 EC in the laterite soils under
laboratory condition 69
36 Metabolites of carbosulfan 25 EC in the coastal alluvial soil under laboratory condition
70
37 Metabolites of carbosulfan granules in laterite soil under
laboratory condition 72
38 Metabolites of carbosulfan granules in the coastal alluvial soil under laboratory condition
73
39 Metabolites formed in the laterite soil by application of
carbosulfan 25 EC in the cropped condition 75
40 Metabolites formed in the coastal alluvial soil by application of carbosulfan 25 EC in the cropped condition
77
41 Metabolites formed in the laterite soil by application of
carbosulfan granules in the cropped condition 78
42 Metabolites formed in the coastal alluvial soil by the application of carbosulfan granules in the cropped condition
80
43 Effect of carbosulfan treatments on the population of soil organisms in laterite soil
81
44 Effect of carbosulfan treatments on the population of soil organisms in coastal alluvial soil
84
xi
LIST OF FIGURES
Figure
No.
Title Between
Pages
1 Degradation pathway of carbosulfan in oranges 20-21
2 Mobility of carbosulfan 25 EC at 100 µg in laterite soil
88-89
3
Mobility of carbosulfan 25 EC at 150 µg in laterite
soil
88-89
4 Mobility of carbosulfan 25 EC at 200 µg in laterite
soil 88-89
5 Mobility of carbosulfan 25 EC at 100 µg in coastal alluvial soil
88-89
6
Mobility of carbosulfan 25 EC at 150 µg in coastal
alluvial soil
90-91
7 Mobility of carbosulfan 25 EC at 200 µg in coastal alluvial soil
90-91
8 Mobility of carbofuran formed from carbosulfan 25 EC at 100 µg in laterite soil
91-92
9 Mobility of carbofuran formed from carbosulfan 25 EC at 150 µg in laterite soil
91-92
10 Mobility of carbofuran formed from carbosulfan 25
EC at 200 µg in laterite soil 91-92
11 Mobility of carbofuran formed from carbosulfan 25 EC at 100 µg in coastal alluvial soil
91-92
12 Mobility of carbofuran formed from carbosulfan 25
EC at 150 µg in coastal alluvial soil 91-92
13 Mobility of carbofuran formed from carbosulfan 25 EC at 200 µg in coastal alluvial soil
91-92
14
Half life of carbosulfan 25 EC in laterite soil under
laboratory and cropped conditions 93-94
xii
15 Half life of carbosulfan 25 EC in coastal alluvial soil
under laboratory and cropped conditions 93-94
16 Half life of carbosulfan granules in laterite soil under
laboratory and cropped conditions 94-95
17 Half life of carbosulfan granules in coastal alluvial
soil under laboratory and cropped conditions 94-95
18 Degradation of carbosulfan 25 EC in laterite soil at 1 mg kg-1 level under laboratory condition
96-97
19 Degradation of carbosulfan 25 EC in laterite soil at 2.5 mg kg-1 96-97
20 Degradation of carbosulfan 25 EC in laterite soil at 5 mg kg-1 96-97
21 Degradation of carbosulfan 25 EC in laterite soil at 1
mg kg-1 level under cropped condition 96-97
22 Degradation of carbosulfan 25 EC in laterite soil at 2.5 mg kg-1 level under cropped condition
96-97
23 Degradation of carbosulfan 25 EC in laterite soil at 5
mg kg-1 level under cropped condition 96-97
24 Degradation of carbosulfan 25 EC in coastal alluvial soil at 1 mg kg-1 level under laboratory condition
97-98
25 Degradation of carbosulfan 25 EC in coastal alluvial
soil at 2.5 mg kg-1 level under laboratory condition 97-98
26 Degradation of carbosulfan 25 EC in coastal alluvial soil at 5 mg kg-1 level under laboratory condition
97-98
27 Degradation of carbosulfan 25 EC in coastal alluvial
soil at 1 mg kg-1 level under cropped condition 97-98
28 Degradation of carbosulfan 25 EC in coastal alluvial soil at 2.5 mg kg-1 level under cropped condition
97-98
29 Degradation of carbosulfan 25 EC in coastal alluvial
soil at 5 mg kg-1 level under cropped condition 97-98
30 Degradation of carbosulfan granules in laterite soil at 1 mg kg-1 level under laboratory condition
97-98
31 Degradation of carbosulfan granules in laterite soil at 2.5 mg kg-1 level under laboratory condition
97-98
xiii
32 Degradation of carbosulfan granules in laterite soil at 5 mg kg-1 level under laboratory condition
97-98
33 Degradation of carbosulfan granules in laterite soil
at 1 mg kg-1 level under cropped condition 97-98
34 Degradation of carbosulfan granules in laterite soil at 2.5 mg kg-1 level under cropped condition
97-98
35 Degradation of carbosulfan granules in laterite soil at 5 mg kg-1 level under cropped condition
97-98
36
Degradation of carbosulfan granules in coastal alluvial soil at 1 mg kg-1 level under laboratory
condition
98-99
37
Degradation of carbosulfan granules in coastal
alluvial soil at 2.5 mg kg-1 level under laboratory condition
98-99
38
Degradation of carbosulfan granules in coastal
alluvial soil at 5 mg kg-1 level under laboratory condition
98-99
39 Degradation of carbosulfan granules in coastal alluvial soil at 1 mg kg-1 level under cropped condition
98-99
40 Degradation of carbosulfan granules in coastal alluvial soil at 1 mg kg-1 level under cropped condition
98-99
41
Degradation of carbosulfan granules in coastal
alluvial soil at 1 mg kg-1 level under cropped condition
98-99
42 Effect of carbosulfan on the microbial population of laterite soil
98-99
43 Effect of carbosulfan on the microbial population of coastal alluvial soil
99-100
xiv
LIST OF PLATES
Plate
No.
TITLE Between
Pages
1 Saturation of the soil column for mobility study 30-31
2 Eluting the soil column after treatment 30-31
3 Cut pieces of soil column for residue analysis 30-31
4 Persistence study under cropped condition 32-33
5 Persistence study under laboratory condition 32-33
6 Enumeration of soil bacteria 34-35
7 Enumeration of soil fungi 34-35
8 Enumeration of soil actinomycetes 34-35
9 Enumeration of soil arthropods 34-35
xv
LIST OF APPENDICES
Plate
No.
TITLE Between
Pages
1 Calibration curve of standard carbosulfan and its metabolites
I
2 Chromatogram of standard of carbosulfan and its
metabolites at 0.005 mg kg-1
II
3 Chromatogram of recovery of carbosulfan and its metabolites from laterite soil
III
4 Chromatogram of recovery of carbosulfan and its
metabolite from coastal alluvial soil
IV
5 Mass spectra of carbosulfan and its metabolite at 0.01 mg kg-1
V
xvi
LIST OF ABBREVIATIONS
@ - At the rate ai - Active ingredient
AINP - All India Network Project % - Per cent
µg - Microgram
BDL - Below Detectable Level
CAS - Chemical Abstract Service
Ca - Calcium
CEC - Cation Exchange Capacity
C D - Critical Difference
CFU - Colony Forming Unit
CIB & RC - Central Insecticide Bureau & Registration
Committee
CIPAC - Collaborative International Pesticides
Analytical Council
CIRCOT - Central Institute for Research on Cotton
Technology
cm - Centimeter
CRD - Completely Randomized Design
CRM - Certified Reference Material
dS - Deci Siemen
DS - Soluble Dust
EC - Emulsifiable Concentrate
EC - Electrical Conductivity
EFSA - European Food Safety Authority
et al - And others
xvii
Ex. Ca - Exchangeable calcium
Ex. Mg - Exchangeable magnesium
FMC - Food Machinery Corporation
Fig. - Figure
g - Gram
G - Granules
h - Hour
ha - Hectare
i.e - That is
IPCS - International Programme on Chemical Safety
K - Potassium
KAU - Kerala Agricultural University
kg - Kilogram
LC - Liquid Chromatography
LOD - Limit of Detection
LOQ - Limit of Quantity
Mg kg-1 - Megagram per kilo gram
Mg m-3 - Megagram per meter cube
Mg - Magnesium
mg - Milligram
Ml - Milli Litre
mm - Millimeter
mM - Millimolar
N - Nitrogen
O.M - Organic matter
P - Phosphorus
ppm - Parts per million
PRRAL - Pesticide Residue Research and Analytical laboratory
xviii
PSA - Primary Secondary Amine
QuEChERS - Quick, Easy, Cheap, Effective, Rugged and Safe
S - Sulphur
S. E - Standard Error
SS & AC - Soil Science and Agricultural Chemistry
USEPA - United States Environment Protection Agency
Var. - Variety
WHC - Water Holding Capacity
xix
Introduction
1. INTRODUCTION
The objective of farming is to provide sufficient and affordable food, fuel
and fibre to human and animals. The conventional system of agriculture is not
sufficient to feed the growing population. At present India is the second largest
populous nation after china in the universe with a population of around 1.25
billion which may reach first position by 2022. Use of high yielding varieties
with good management practices and mechanization resulted in the enormous
increase in the agriculture production and hence became intensive. Along with
this, the loss of agriculture produce by weeds, insects, disease, rats etc were
significantly increased. It was reported that, 30 per cent crop yield potential in
India is being lost due to disease, insects and weeds, and in terms of quantity, it is
about 30 Mt of food grain. In order to minimize these losses, use of pesticides
were popularized and became an inevitable input in the modern agriculture sector.
India is using very less amount of pesticide when compared to other developed
countries, India has a per hectare consumption of 0.6 kg pesticide (Mannocsa,
2009).
Among the various pesticides used, furadan, a 3 per cent granular
formulation of carbofuran manufactured by Food Machinery Corporation (FMC)
has been the largest selling granular insecticide in India since 1970s. In
India, carbofuran was registered for more than 25 crops and has a special place in
Indian agriculture. Even after four decades of its introduction in India, it
continued to be one of the most preferred insecticides for rice, banana and
sugarcane. In terms of toxicity, carbofuran was categorized under extremely toxic
insecticide with red label. Due to its high mammalian toxicity (LD50 8-18 mg kg-1
for rat) its use was discontinued in Kerala in 2011 and fourteen chemicals, with
less mammalian toxicity including carbosulfan were suggested as the alternative
for carbofuran to prevent the attack of nematodes in rice, banana, brinjal and
cardamom. Carbosulfan was also suggested as a replacement for phorate, which
was used for controlling pest attack in paddy
1
(Anon., 2011). Carbosulfan is coming under the category of highly toxic with
blue label, used against sucking and lepidopteran pest with an LD50 value of 101-
250 mg kg-1 for rats and hence was considered to be relatively safe for handling.
It acts on the insect by inhibiting the activity of acetylcholine esterase.
Carbosulfan get metabolized to carbofuran, 3 keto carbofuran, 3- hydroxy
carbofuran and to certain phenol derivatives. So, the toxicity of carbosulfan is not
only due to carbosulfan itself, but with these primary metabolite compounds also.
It is also manufactured by FMC and was available as Emulsifiable Concentrate
(25 EC), Granules (6 G) and as Soluble Dust (25 DS). It was recommended for
use in rice, chilli and cotton by Central Insecticide Bureau & Registration
Committee (CIB & RC) at 250 g ai ha-1 and in rice, cardamom and banana by
KAU @ 16.7 kg ha-1 of carbosulfan 6 G. But irrespective of the recommendation,
the farmers are using carbosulfan in higher dose in the field and even in the poly
houses. It was reported that, carbosulfan creates certain chromosomal aberrations
in rat and has inhibitory effect on soil microbes. Even though its parent
compound is less toxic, the metabolites have the same toxic effect as that of
carbofuran. With careless application of carbosulfan, there may be a chance of
more lethal effect than carbofuran due to the toxicity from the parent compound
as well as from metabolites and sometimes the higher concentration of application
may even lead to contamination of the surface water bodies or even the
underground water. So, there was an urgent need to study the transport and
transformation process of carbosulfan in soil. Since it is a widely used soil
pesticide against nematodes in Kerala, it was studied in two prominent soil types
of Kerala, viz., laterite (Sandy Loam) and coastal alluvial soil (Loamy Sand). The
study on persistence and degradation was done using the widely used two
formulations on carbosulfan such as EC and granules in the laboratory and in the
cropped conditions, with chilli (Ujwala variety) as the test crop in order to
compare the variation in persistence of carbosulfan in soil with and without the
crop.
2
The main objectives of the experiment were,
To study the persistence of carbosulfan in laterite and coastal alluvial soils
of Kerala under laboratory and cropped condition with EC and granule
formulation
To study the metabolism of carbosulfan in soil by monitoring the
formation of metabolite in the soil from 0 th day to 30th day (upto Below
Detectable Level) after Emulsifiable Concentration (EC) and granule (G)
treatment.
To study the mobility of carbosulfan 25 EC in laterite and coastal alluvial
soil columns
To study the effect of carbosulfan on soil organisms (bacteria, fungi
actinomycetes and arthropods) by application of carbosulfan 25 EC and
granule in normal and double doses.
3
Review of Literature
2. REVIEW OF LITERATURE
The term pesticide includes compounds like fungicides, herbicides,
insecticides, nematicides, plant growth regulators, rodenticides, molluscicides and
others. A pesticide should be lethal to the target organism, but it should not produce
any harmful effect on the non-target species such as man and other mammals and
should disappear after performing its pesticidal action.
Carbosulfan is a carbamate pesticide belongs to highly toxic category. The
mechanism of toxicity of carbosulfan is based on reversible inhibition of acetyl
cholinesterase (for carbamates generally). It is recommended for use in rice, banana,
cotton and chilli and considered to have moderate persistence in soil. It is used
widely as a substitute for carbofuran, irrespective of its recommendation by CIB &
RC. In this context, a study was conducted to understand its persistence, degradation,
mobility and also its effect on soil organisms in two soil types of Kerala viz., laterite
and coastal alluvial soils in cropped as well as non cropped condition. The previous
works that related to above topic is reviewed under the below heads.
2.1 PESTICIDE USE SCENARIO
Mathur (1999) reported that, in India the 76 per cent of the pesticide used are
insecticides, as against 44 per cent globally. Reports shows that, among the various
states using pesticides, Uttar Pradesh is the largest consumer followed by Punjab,
Haryana and Maharashtra. Regarding the pesticide share across agricultural crops,
cotton account for 45 per cent followed by rice (25%), chillies/ vegetables/ fruits (13-
24%), plantations (7-8%), cereals/ millets/ oil seeds (6-7%), sugarcane (2-3%) and
others (1-2%), (Abhilash and Singh, 2009). The pattern of pesticide usage in the
world indicates that, in developed countries among the various pesticides, herbicides
are mostly used (Zhang et al., 2011).
4
2.1.1 Benefits of Pesticides
Large number of benefits has been derived from pesticide use in forestry,
domestic use and in public health and definitely in agriculture sector, upon which the
Indian economy is largely dependent. It played a major role in the increase of food
grain production from 50 million tons in 1948–49, to almost 5 folds to 240 million
tons by the end of 2010 from 169 million hectares of permanently cropped land.
Pesticides have been a vital input contributing to the production and productivity of
crops reducing the losses due to insect pests, weeds which inturn can considerably
reduce the quality and quantity of produce.
Warren (1998) reported that, in the 20th century tremendous increase in the
crop yield is noted in United States by the use of pesticides. Similarly Webster et al.
(1999) reported that, considerable economic loss is monitored in the crop yield
without pesticides and when pesticides were applied it showed significant yield
increase.
Kole et al. (1999) identified that, in the environment the pesticides are
subjected to photochemical / biochemical transformation to produce metabolites
which are comparatively less-toxic than the parent compound to both human beings
and the environment but sometimes it may leads to more toxic compound also.
2.1.2 Disadvantages of Pesticides
Pesticides can contaminate soil, water or other natural bodies. In addition to
controlling insect pests or weeds, pesticides can be lethal to natural enemies including
birds, fishes, aquatic organisms and non-target plants. Insecticides are generally
categorized under acutely toxic class of pesticides, but herbicides can also pose risks
to non-target organisms. In a study it has been estimated that, less than 0.1
percentage of the pesticide applied to crops actually reaches the target pests while 99
percentage of the pesticide enters the environment directly or indirectly,
5
contaminating soil, water and air, where it can adversely affect non-target organisms
(Carriger et al., 2006). Pesticides can even reach the water bodies through runoff
from treated plants and soil. Contamination of groundwater by pesticides is also
widespread. Abhilash and Singh (2009); Vijgen et al. (2011) reported that, pesticides
that exhibit high persistency especially like DDT, organochlorine, endosulfan, endrin,
heptachlor, lindane and their transformation products (TPs). Even though most of
them are now banned still their residues are found in the soil.
2.2 MOBILITY OF PESTICIDES
Mobility may result in redistribution of pesticide within the application site or
movement of some amount of pesticide off site. Pesticides that leach through soil
column may reach ground water.
At least 143 pesticides and 21 of their transformation products have been
found in ground water, from every major chemical class (Anon., 2009). Pesticides
frequently detected in ground water are triazine and acetanilide herbicides that were
used extensively on corn and soybeans. Carbamate insecticides such as aldicarb
cause ground water contamination problems (Toth and Buhler, 2009).
Pesticide contamination of ground water is a natural issue because ground
water is used for drinking by 50 percentage of the population. Concern about
pesticides in ground water is especially acute in rural agricultural areas where over 95
percent of the population relies upon ground water for drinking (Begum et al., 2008).
Mobility is affected by many factors, such as soil and pesticides properties,
topography, canopy, ground cover, soil organic matter, texture, structure and crop
management practices which inturn govern the potential for groundwater or surface
water contamination by pesticides (Kerle et al., 2007). Ferencz and Balog (2010)
reported that, polar pesticides are important and they mainly includes carbonates,
fungicides and some organophosphorus insecticides and their Transformation
6
Products (TPs), which can be moved from soil either by runoff or leaching, thereby
contributing to contamination of water sources.
Field soils show considerable variations in properties such as clay content,
organic matter, bulk density and moisture that can affect the mobility and thus the
fate of pesticides in the soil environment (Di and Aylmore, 1997). Soil properties
(organic matter, soil texture and soil acidity), pesticide properties (solubility,
adsorption and persistence), pesticide application (rate of application and application
method) and weather conditions are the factors affecting leaching (Osman and
Cemile, 2010).
Study by Rice and Cherniak (1997); Gabarino et al. (2002) showed that,
pesticides including new generation pesticides like chlorothalonil, chlorpyrifos,
metalachlor, terbufos and trifluralin have been detected in Arctic environmental
sample.
Mc Connell et al. (1997); Lenoir et al. (1999); Thurman and Cromwell
(2000); Harman et al. (2003) identified the presence of new generation pesticides in
the Sierra Nevada mountains. Studies by Muir et al. (2004) have identified the ability
of some of these new generation compounds to undergo short-range atmospheric
transport to ecologically sensitive regions such as the Chesapeake Bay. High levels
of pesticides chlordecone were detected in coastline, rivers, sediments and
groundwater in the Caribbean island of Martinique due to its massive application on
banana plantations (Bocquene and Franco, 2005).
2.3 PERSISTENCE OF PESTICIDES
The term persistence was introduced into the pesticide scientific literature
to describe the continuing existence of certain insecticides in the environment and is
now applied to any organic chemical that has biological activity. However, from an
environmental point of view, molecules that persist in nature are undesirable for
7
many reasons. Some are intrinsically toxic and deleteriously affect humans, animals,
agricultural crops, wildlife, fish and other aquatic organisms, or microorganisms.
According to Navarro et al. (2007), persistence may be defined as the
tendency of the pesticide to conserve its molecular integrity, physical, chemical and
biological characteristics in a medium through which it is distributed and transported.
According to Beevi et al. (2014), residues of pesticides like DDT and
endosulfan residues were found in cardamom soils of Idukki district even though they
were not applied in these soils for the past 10 years which reveals the high
persistence nature of these pesticides.
Alexander (2000) reported that, the longer the molecule remains in the
environment, the greater is the exposure of susceptible individuals or populations and
greater is the risk or harmful effects. In a similar study Ryang et al. (1988) reported
that, the half-lives of alpha endosulfan and ethoprophos were 6 and 12 days longer
under poly ethelene mulching than under non-mulching conditions under red pepper
cultivation. In a study Gevao et al. (2000) reveals that, when the adsorption of a
pesticide is high its availability in the soil solution decreases, as a result the material
available to biota also decreases and the adsorption process will increase with
increase in the surface area of the clay or with increasing the organic matter content
of the soil.
Usually the persistence is expressed in terms of half life of the pesticide.
Half-life is the time it takes for a certain amount of a pesticide to be reduced by half.
This occurs as it dissipates or breaks down in the environment. According to Hanson
et al. (2015), a pesticide will break down to 50 percentage of the original amount
after a single half-life, 25 percent will remain after two half-lives and 12 percent will
remain after three half-lives. This continues until the amount remaining is nearly
8
zero. In general, the longer the half-life, the greater the potential for pesticide
movement.
Kerle et al. (2007) reported that, pesticides can be divided into three
categories based on half-lives: non persistent pesticides with a typical soil half-life of
less than 30 days, moderately persistent pesticides with a typical soil half-life of 30 to
100 days, or persistent pesticides with a typical soil half-life of more than 100 days.
Table 1. Environmental factors influencing the pesticide persistence (Hanson et al.,
2015).
In tropical soil, due to acidic nature, the H+ ion concentration is high and it has
a positive charge and can adsorb anionic molecules while in alkaline soil it can
adsorb positively charged pesticides (Calvet, 1989). According to Liu et al. (2000)
Environmental Factors Role in Persistence
Sunlight Radiation breaks chemical bonds and create secondary
products
Microbes Bacteria and fungi can break down chemicals, creating
biodegradation products
Plant / animal metabolism Plants and animals can change chemicals into forms
that dissolve better in water (metabolites)
Water Water breaks chemicals thus dissolve better in water
Dissociation Chemicals can break apart into new products
Sorption Chemicals that stick tightly to particles thus restricted
from moving away
Bioaccumulation Some chemicals can be absorbed by plants/animals
from the soil, water, food, and air
9
ionisation determines the charge of the pesticide and hence its adsorption to the clay
particle. Volume and branching as well as the electronic structure influences the
adsorption process by the nature and arrangement of the functional group in it
(Barriuso et al., 2008). The adsorption of glyphosate is high even it is highly soluble
and this is because it forms anionic group on dissociation and that will bind with the
Fe and Al present in the soil. Here the process of adsorption is very high than the
solubilization and thereby it is highly adsorbed to the soil particle (Mamy and
Barriuso, 2005).
For nonpolar pesticides, the increase in water content decreases the adsorption
process. Since water is highly polar than the pesticides it will compete for the
adsorption site, thereby reduce the adsorption process (Roy et al., 2000). With
increasing depth, adsorption decreases because of low organic matter (Coquet and
Barriuso, 2002). According to Andreu and Pico (2004), the acidic situation enhances
the adsorption for ionizable pesticides like 2,4-D,2,4,5-T, picloram, and atrazine.
Organic matter increases the surface area as well as the proliferation of
microbes leading to chelation of the pesticides in soil and hence ultimately lead to
increase in adsorption (Benoit et al., 2008). In kaolinite soil, the adsorption is less
because of less surface area while in montmorillonite the adsorption is high since it is
an expanding clay mineral. In sandy loam soil, the adsorption of endosulfan is
comparatively less (George et al., 2009).
According to Edwards et al. (2009), with increasing soil moisture by increase
in rainfall, the hydrophilic nature of OM increases, hence the area for adsorption also
increases. In non tilled soil, the adsorption is high, because in less disturbed soil, the
organic matter is very high (Larsbo et al., 2009).
For physical adsorption where the force of attraction is weak. Temperature
decreases the process of adsorption and if the adsorption is chemical in nature
(electrostatic forces), it will increase with increase in temperature, ie, temperature
10
helps better ionization of the pesticide and that will leads to the better adsorption
(Hulscher and Cornelissen, 1996). But according to Osman and Cemile (2010), with
high rainfall, sometimes highly soluble pesticide may leach away and thus became
very less to be adsorbed to the soil. Time has also an influence on the adsorption,
with change in time, the rate of adsorption changes. In certain cases, the rate may
increase or decrease due to the process of degradation (Mamy and Barrisuo, 2007).
2.4 DEGRADATION OF PESTICIDES IN SOIL
A pesticide applied for pest control purpose will get converted to metabolites
generally called as transformation products. A large number of transformation
products (TPs) were recorded from various pesticides (Barcelo and Hennion, 1997;
Roberts, 1998; Roberts and Hutson, 1999). The degradation can be biotic or abiotic.
Abiotic degradation takes place mainly through photochemical or thermochemical
ways, while biotic degradation is through biochemical reactions mediated by
microbes (Graebing et al., 2003).
2.4.1 Degradation of Pesticides by Light (Photo Degradation)
The direct photolysis of pesticides on the soil surface is restricted to a depth of
0.2- 0.3 mm while mean indirect photolysis is restricted to 0.7 mm for the out door
experiments (Herbert and Miller, 1990). Photochemical transformations occur
commonly in the soil and they may totally destroy or appreciably modify a number of
different types of pesticides (Konstantinou et al., 2001). However, such processes
rarely convert pesticides to inorganic compounds in soils, and many of these
reactions only bring about a slight modification of the molecule so that the
metabolites are frequently similar in structure, and often in toxicity to their parent
precursors.
11
2.4.2 Degradation of Pesticides by Microbes (Biochemical Degradation)
Biochemical degradation depends on the behaviour of the pesticides, organic
carbon content, pH of the soil, biological activity and distribution of the microbes,
temperature and moisture content (Rodriguez et al., 2001).
The soil organic carbon content generally had a positive influence on
degradation (Guo et al., 2000). A small content of the organic matter in the soil can
increase the pesticide volume in a particular area by binding with that pesticide and
that also helps in the degradation of the pesticide (Lotter et al., 2003). In some cases,
the photochemical pre-treatment integrated with microbial degradation will lead to
complete degradation and detoxication of some pesticides as occurs with atrazine
(Chan et al., 2004).
Some microorganisms are capable of using certain pesticides as their only
source of carbon and nitrogen, like Pseudomonas (with 2,4-D and paraquat),
Nocardia (with dalapon and propanyl) or Aspergillus (with trifluralin and picloram).
Also the increase in microbial activity with atrazine pollution was noticeable after
lengthy incubation (Moreno et al., 2007). There is almost no biodegradation of
chlordecone (organochlorine insecticide) because of its highly chlorinated cage-like
structure that makes chlordecone a poor carbon source for bacteria (Cabidoche et al.,
2009).
2.5 EFFECT OF PESTICIDES ON SOIL ORGANISMS
Pesticides interact with soil organisms and their metabolic activities may be
altered (Singh et al., 2002). The residues of pesticides can harm non target organisms
including animals ranging from beneficial soil microorganisms soil insects, non-
target plants, fish, birds, and other wildlife. A study on the effect of pesticide effects
on earthworms showed severe negative effects on growth and reproduction (Shahla
and Dsouza, 2010).
12
An integrated study on a Round-up resistant soya field in Argentina showed
that, deleterious effect of these pesticides on earthworm population (Casabe et al.,
2007). Similarly microbes related study conducted in orchards in the South Africa
indicated adverse effects of spraying with pesticides (chlorpyrifos and azinphos
methyl) on earthworm’s biomass and cholinesterase activity and concluded that,
earthworms were detrimentally affected by the pesticides due to chronic and
intermittent exposure (Reinecke and Reinecke, 2007). Studies revealed that,
glyphosate affect the predatory arthropods and cause behavioural changes in them
(Evans et al., 2010)
Decrease in the number of spiders and richness of collembolan were noticed
after application of chlorpyrifos (Fountain et al., 2007). Studies revealed that,
glyphosate affect the predatory arthropods and cause behavioural changes in them.
U.S. Geological Survey (1999); US EPA (2000) found that chlorpyrifos, a common
contaminant of urban streams, is highly toxic to fish, and causing fish death in
waterways near treated fields or buildings.
2.6 CARBAMATE PESTICIDES – INTRODUCTION
The carbamates pesticides were mainly used in agriculture as insecticides,
fungicides, herbicides, and nematicides. In addition, they are used as biocides for
industrial or other applications and in household products and in public health vector
control. Thus, these chemicals are a part of the large group of synthetic pesticides
that have been developed, produced, and used on a large scale in the last 40 years.
The general formula of the carbamates is:
O
|| H
R1- C –N
R2
13
where R1 and R2 are alkyl or aryl groups.
The light absorption characteristics of carbamates contribute to their rapid
decomposition (by photodegradation or photodecomposition) under aqueous
conditions. Thus, the hazards of long-term contamination with carbamates were
comparatively less. Carbamate insecticides are mainly applied on the plants, and can
reach the soil while carbamate nematicides and herbicides are applied directly to the
soil.
Carbamates are toxic for worms and other organisms living in the soil.
Although a great reduction in the earthworm population may occur when applying
carbamates to the soil, numbers will return to normal, because of the rather rapid
breakdown of these compounds (IPCS, 1982).
Matthew et al. (2007) observed that enzyme mediated degradation takes
place in the case of carbamate pesticides. The largest proportion of bound residues
was found for carbamates, and in particular, for dithiocarbamates. In this study,
authors further summarized and discussed factors that affect formation of bound
residues, viz., chemical properties as well as soil and environmental conditions
(Barriuso et al., 2008). In a lab study for understanding the persistence of 6
carbamate pesticides oxamyl, carbaryl, phorate, phosphamidon, carbofuran, and
methomyl on ten soils of Aligarh district under different temperatures, concentration,
FYM, nitrogen concentration, pesticide concentration, and pH range revealed that,
degradation of the pesticide increased with high temperature, FYM, nitrogen and
moisture while it was slow with increased pesticide concentration. The degradation
was rapid in alkaline soil than neutral or acidic soil (Bansal, 2009). Barra et al.
(2010) noted that, the microbial concentration in the soil increased with decrease in
the concentration of aldicarb and carbofuran.
14
Several factors influence the biodegradation of carbamates in soil, such as
volatility, soil type, soil moisture, adsorption, pH, temperature and
photodecomposition (Osman and Eldib, 1972). Environmental conditions that favour
the growth and activity of microorganisms also favour the degradation of carbamates.
The first step in the metabolic degradation of carbamates in soil is hydrolysis. The
hydrolysis products will be further metabolized in the soil-plant system.
Certain carbamates may reach groundwater and as a result it may
contaminate drinking-water. In certain cases, the use of toxic carbamates may cause
a significant reduction in non-target organisms. Contamination of groundwater and
drinking water sources by aldicarb, a carbamate was also reported (Soren and Stelz,
1991).
2.7 CARBOSULFAN
Carbosulfan is a systematic insecticide belonging to the carbamate class and is
the pro-insecticide of carbofuran. It is not very stable, it decomposes slowly at room
temperature. Carbosulfan is used as an insecticide, nematicide and acaricide. When it
gets degraded, it forms carbofuran which is a banned pesticide in Kerala due to its
toxicity. The European Union banned the use of carbosulfan in 2007. Its
oral LD50 for rats is between 90 to 250 mg kg-1, and is only slightly absorbed
through skin (LD50 > 2000 mg kg-1 for rabbits).
2.7.1 Salient Features of Carbosulfan
Common name: Carbosulfan
Chemical name: 2, 3-di hydro-2, 2-di methyl benzo furan-7-
yl (di butyl amino thio) methyl carbamate
CAS Registry No.: 55285-14-8
CIPAC No: 417
Synonyms: FMC 35001, Marshal, Sheriff
15
Molecular Structure
Odour No specific odour
Molecular formula: C20H32N2O3S
Molecular weight: 380
Vapour pressure: 2.69 x 10-7 mm Hg at 25°C
Melting point: Carbosulfan is a liquid. It decomposes at elevated
temperature
Boiling point 219.3°C
Hydrolysis Hydrolyzes at pH < 9
Photolysis Mainly to carbofuran and dibutyl amine in aqueous
solutions
Half-life 1.4 days at pH 7
4-8 days in distilled water
Solubility in water 0.3 mg L-1 at pH 9 and 25°C
Solubility at 23°C Miscible in all proportions in hexane, toluene, acetone
and acetonitrile
Solubility at 20°C >250 g L-1 in dichloro methane, methanol and ethyl
acetate
2.7.2 Carbosulfan as a Crop Protectant
Carbofuran is generally applied as granules to flooded rice paddies or as a
spray to the basal portion of leaf sheath. Carbosulfan is an analog of carbofuran
developed and recommended for use as an effective substitute for carbofuran. It has
been reported to be very effective against the insect pests, which can not be
controlled by organo-chlorine or organophosphorous insecticides (Sahoo et al.,
1990). It has been proposed for the control of pyrethroid resistant mosquitoes
16
(Guillet et al., 2001). Cabosulfan is used as an alternative of endosulfan 35 per cent
EC and 4 per cent DP in paddy against gall midge and stem borer, in cotton against
aphids, jassids and thrips and in chilli against thrips. Carbosulfan is widely used in
agriculture as a broad spectrum insecticide against caterpillars, green leaf hoppers,
white - backed plant hoppers, brown plant hoppers, gall midges, stem borers, leaf
folder of paddy and white aphids of chilies (Giri et al., 2002).
Hot water treatment at 50°C for 30 minutes followed by foliar spraying of
carbosulfan 0.1per cent at 40 days after transplanting reduced white tip nematode by
34 per cent, thereby increasing rice yield by 87 per cent over un treated control
(ICAR, 2010). Carbosulfan 6 per cent G and carbosulfan 25 per cent EC were
recommended in chilli while carbosulfan 25 per cent DS was recommended in cotton.
Treatment of cotton seed with carbosulfan at 20g kg-1 of seed or imidacloprid at 7.5g
kg-1 seed was introduced as a new protection technique against aphids and jassids
(CIRCOT, 2002).
In rice, Carbosulfan 6 per cent G at1000 g ai ha-1 is recommended against
stem borer, gall midge, leaf hopper and leaf folder, while a dosage of 200-250 g ai
ha-1 of carbosulfan 25 EC against Brown Plant Hopper (BPH), Green Plant Hopper
(GPH), white aphid and leaf folder in chilli. In cotton, 15 g carbosulfan 25 per cent
DS per kg seed is recommended against jassids, aphids and thrips (CIBRC, 2012).
Carbosulfan 6 G is recommended @ 6.7 kg ha-1 as a substitute for carbofuran
3 G in rice against stem borer, gall midge, BPH, GLH, hispa and against nematodes
in rice, banana and cardamom (KAU, 2011).
2.7.3 Movement of Carbosulfan in Plant and Soil
The insecticide compounds concentrations in the foliage of brussels sprouts,
cauliflower and sugar beet crops were higher when they were higher in the soil. At
harvest, no residue of either carbosulfan, furathiocarb, carbofuran, or any of its
17
metabolites were observed in the flower of cauliflower, or in the brussels sprouts
themselves (Rouchard et al., 1990).
During plant growth, each of the insecticides (and their soil metabolites) was
transported from soil into the plant foliage, where it could give a secondary plant
protection against the foliage insects by transporting to plant from soil. For systemic
insecticides such as carbofuran, carbosulfan and furathiocarb, the weights per plant of
insecticide compounds transported from soil into the foliage were greater than they
were with the non systemic chlorpyrifos and chlorfenvinphos (Rouchard et al., 1991).
Continuous use of carbosulfan and carbofuran in soils leads to contamination
of surface water bodies (Thapinta and Hudak, 2000). Lysimetric studies on the
movement of carbosulfan and monocrotophos showed the presence of residues at the
bottom of lysimeter at 1.52 > 2.1 > 2.74 m, that means the concentration of residues
were decreasing at higher water table depth (Ilyas et al., 2010).
2.7.4 Persistence of Carbosulfan
Studies on the dislodgeable residues of carbosulfan and three of its major
metabolites in leaves, fruits and soil in an orange grove in Florida showed that,
carbosulfan and carbofuran dissipation were rapid in fruits during fall season (3- 4
folds in 3 days) and slower during winter seasons (1.5 time in 3 days). In both
periods the persistence has higher in soil than in fruit and leaves (2-3 folds in 8 days).
Most important metabolite of carbosulfan is carbofuran which persisted more than the
parent material in orange leaves in both seasons ( Nigg et al., 1985). Reports reveals
that, carbosulfan and its major metabolite carbofuran have low persistence in water
and have medium persistence in soil solution of tropical low land rice fields and
irrigated rice fields (Pedro et al., 2005).
18
When carbosulfan was added to sand and a medium of sand and organic
matter, the bioavailability is more in pure sand medium indicating that the organic
matter fixes the pesticide and thus reduces its toxic effect( Hautier et al., 2007).
The studies on the persistence of carbosulfan in red loam, alluvial and black
soil revealed that, the carbosulfan residues reached below detectable level within 75
days in red loam and alluvial soils while 90 days in black soil. The half life of
carbosulfan were 15, 12, and 14 days in black, red and alluvial soils respectively at 5
mg kg-1 level of fortification, while the half life were 12,10 and 11 days at 10 mg kg-1
level of fortification (Kamala and Chandrasekaran, 2015).
2.7.5 Degradation of Carbosulfan
Carbosulfan is chemically stable under alkaline conditions, but undergoes
rapid chemical hydrolysis (Ramanand et al., 1989) to carbofuran and dibutyl amine at
pH below 6 (Sahoo et al., 1990). In the environment, carbosulfan is first metabolized
to carbofuran, then to 3-hydroxy-carbofuran and thereafter to 3-keto carbofuran. This
is a special case in which a less toxic pesticide (carbosulfan, LD50, 101- 250 mg kg-1
for rats) is transformed to a more toxic one (carbofuran, LD50 8 mg kg-1 for the same
species). Under field conditions, the toxic effect of carbosulfan is mainly due to the
transformation to its carbofuran metabolite (Tomlin,1995).
The pesticide dissipation in rice - fish production system revealed that,
carbosulfan is rapidly converted to carbofuran in all rice eco-system components,
except for the rice leaves where its occurrence as the original compound lasted 7
days. Carbofuran was the main metabolites which persisted for 30 days in soil
(Varca et al., 1998). Carbosulfan on one hand and the sum of carbofuran, 3-hydroxy
carbofuran and 3- keto carbofuran and their conjugates on the other hand were
considered as the relevant residues to assess the consumer exposure and risk (EFSA,
2009).
19
2.7.6 Effect of Carbosulfan on Organisms
Effect of carbosulfan on soil microflora on arable soil receiving single
application produced significant biomass reduction while repeated application of
carbosulfan did not show any detectable deleterious effect on soil microbial biomass,
thereby suggesting substantially different effect on soil biomass produced by single
or repeated application of pesticide (Duah and Johnson, 1996). Carbosulfan has been
reported to induce chromosome aberrations in rat (Topaktas et al., 1996).
Carbosulfan @ 1, 2 and 10 per cent of recommended field rate when applied
to the soil showed the increase in mortality rate of beneficial insects Bemidion
lambros by 50, 57 and 100 per cent respectively (Hautier et al., 2007). Carbosulfan
treated soil had less evolution of CO2 indicating initial inhibitory effect on microbial
activity and that gained positive stimulation with time. (Latif et al., 2008). It is noted
that, the seed treatment of chickpea with aqueous solution of carbosulfan declined
Melodogyne. incognita population in the soil by 38-70 percent, while R. reniformis
by 32-66 percent (Meher et al., 2010). Carbosulfan is extremely toxic to mammals
and its toxicity is mediated through inhibition of acetyl choline esterase enzyme.
(Karami-Mohajeri and Abdollahi, 2010).
20
Fig. 1. Degradation pathway of carbosulfan in oranges (Carla et al., 2005)
Materials and Methods
3. MATERIALS AND METHODS The present study entitled “Persistence and transformation of carbosulfan in
laterite and coastal alluvium soils of Kerala and its effect on soil organisms” has been
carried out to assess the dynamics of carbosulfan in laterite and coastal alluvial soils
under laboratory as well as cropped conditions using Emulsifiable Concentrate (EC)
as well as Granule (G) formulations of the pesticide, to study its migration tendency
in the packed soil columns and also to study the effect on soil organisms.
3.1 PHYSICO- CHEMICAL ANALYSIS OF SOILS
The study was conducted in two types of soils viz., sandy loam and loamy
sand soils of Kerala. The laterite soil was collected from the identified locations of
College of Agriculture, Vellayani, Thiruvananthapuram, Kerala, while coastal
alluvial soil was collected from various locations near Kazhakkoottam,
Thiruvananthapuram, Kerala at a depth of 0-15 cm using a spade. Along with this,
core samples were also taken for the physical analysis. The collections were done
during September 2015. The collected soil samples were spread, mixed and shade
dried for one week and the physico- chemical analysis of the two soils were carried
out as per standard procedures given in Table 2.
3.2 VALIDATION OF MULTI RESIDUE METHODS FOR PESTICIDE RESIDUE
ANALYSIS IN SOIL
A mixture of the analytical standards of carbosulfan and its metabolites viz.,
carbofuran, 3- hydroxy carbofuran and 3- keto carbofuran were fortified in soil at
three different levels ( 0.05, 0.25 and 0.5 mg kg-1). Extraction and clean up methods
were performed by adopting QuEChERS multi residue estimation method.
3.2.1 Technical programme
Design: CRD
21
Table 2. Analytical methods followed to test the physico chemical parameters in soil
Sl.
No Parameter Method Reference
1 Texture International pipette method Piper ( 1966)
2 Bulk density Core method
Gupta and Dakshnamoorthy
(1980)
3 Particle density Pycnometer method
Gupta and Dakshnamoorthy
(1980)
4
Water Holding
Capacity (WHC) Core method
Gupta and Dakshnamoorthy
(1980)
5 Field capacity Pressure plate apparatus
Gupta and Dakshnamoorthy
(1980)
6 pH pH meter with glass electrode Jackson(1973)
7
Electrical
Conductivity (EC) Conductivity meter Jackson(1973)
8
Cation Exchange
Capacity (CEC)
Neutral N ammonium acetate
method Jackson(1973)
9 Organic carbon Walkley and Black method Jackson(1973)
10 Available Nitrogen Alkaline permanganate method Jackson(1973)
11
Available
Phosphorus
Bray No 1 extraction and
Spectrophotometry Jackson(1973)
12 Available Potassium
Neutral N ammonium acetate
extraction & Flame Photometry Jackson(1973)
13 Exchangeable Ca Versanate method Jackson(1973)
14 Exchangeable Mg Versanate method Jackson(1973)
15 Available Sulphur Turbidimery method Jackson(1973)
22
Treatments:3
Replication: 6
Treatments
T1- 0.05 mg kg-1 analytical standard mixture
T2- 0.25 mg kg-1 analytical standard mixture
T3- 0.50 mg kg-1 analytical standard mixture.
3.2.2 Laboratory Glass Ware, Chemical Reagents and Equipments
The glass wares, chemical reagents and equipments used for the study were
given in Table 3. The reference analytical standards of the pesticides were purchased
from Sigma Aldrich, USA and stored in deep freezer at a temperature below -20 °C,
without exposure to light and moisture.
Initially, the glass wares were washed with tap water and then they were
immersed overnight in 1 per cent laboline and then again washed with tap water.
After that, they were dipped in boiling water for 2 hrs and rinsed with acetone and
were kept in the oven at 50 0C for 3 hrs for drying. The plastic tubes were similarly
washed and kept at room temperature for drying. The syringes were thoroughly pre-
rinsed with acetone and then with methanol before use.
3.2.3 Preparation of Mixture of Standard Insecticides
The steps involved in the preparation of standard mixture of carbosulfan and
its metabolites were as follows
3.2.3.1 Procurement of Certified Reference Material (CRM)
The CRMs of carbosulfan, carbofuran, 3-OH carbofuran and 3-keto
carbofuran were procured from M/S. Sigma Aldrich, USA. Required quantities of
23
Table 3. The glass wares, equipments, and reagents used for residue analysis
Laboratory Glass wares Chemical Reagents Equipments
Beakers 100, 250, and 500
mL
Acetone AR grade Analytical Balance
Centrifuge tubes 15 mL
and 50 mL
Acetonitrile HPLC grade Laboratory centrifuge
Class A pipettes 0.5 mL, 1
mL, 2 mL, 10 and 20 mL
Magnesium sulphate
(hydrated) AR grade
Mechanical shaker
Conical flasks and
standard flasks 250 mL,
500 mL and 1 L
Methanol HPLC grade Vortex shaker
Graduated test tubes 5mL
and 10mL
Primary Secondary Amine TurboVap Evaporator
Micro pipettes 100 µl, 1
mL and 5mL
Sodium chloride (AR
grade)
Rotory vacuum flash
evaporator
Separating funnels 750
mL and 1 L
Ammonia solution Liquid Chromatograph -
Mass Spectrometer
TurboVap tubes 20 mL
and 30 mL
Dichloromethane
PVC pipes (50 x 2.5cm) Sodium Sulphate
Hypodermic syringe 10
mL and Randisc
24
each of the standards were weighed to prepare the analytical standard solutions of
known concentrations.
Table 4. Details of CRMs used for the preparation of pesticide mixture
Sl.
No
Compound Formula CAS Number Purity
1 Carbosulfan C20H32N2O3S 55285-14-8 99.4%
2 Carbofuran C12H15NO3 1563-66-2 99.9%
3 3-OH Carbofuran C12H15NO4 16655-82-6 99.1%
4 3-Keto Carbofuran C12H13NO4 16709-30-1 98.5%
3.2.3.2 Preparation of Standard Solution
Standard stock solutions of carbosulfan and its metabolites (1000 mg L−1)
were prepared in methanol and stored at -20°C in deep freezer.
3.2.3.3 Intermediate Stock Solution and Working Standards
Intermediate standards of 100 mg kg-1 of carbosulfan and its metabolites were
prepared by diluting the required quantity of stock solution with methanol.
Aliquots of intermediate standards were taken in separate standard flasks in
order to prepare working standards of 10 mg kg-1 of each compound. From this
working standard (10 mg kg-1) a mixture of all these four compound were prepared in
methanol solvent and stored in refrigerator for further use. From this, working
standard serial dilution was done to obtain 1, 0.5, 0.25, 0.1, 0.05, 0.025 and 0.01 mg
kg-1 concentrations. The individual standards of different insecticides were injected
in Liquid Chromatography – Mass Spectrometer and a calibration curve was prepared
by plotting concentration vs. peak area.
25
3.2.4 Fortification of Soil with Standard Insecticide Mixture
A fixed quantity of 10 g each of air dried (2 mm sieved) soil samples were
taken in 18 50 mL centrifuge tubes and were spiked separately with 0.05 mL, 0.25
mL and 0.5 mL each of 10 mg kg-1 working standard mixture to get 0.05, 0.25 and
0.5 mg kg-1 levels respectively.
3.2.5 Recovery Experiment
A recovery experiment was conducted to standardize the procedure for
extraction and clean up processes. The experiment was conducted by adding a known
quantity of insecticide mixture to soil and trying the extraction process using different
solvent systems. All the chemicals and solvents used in the research were either of
analytical grade or HPLC grade.
3.2.5.1 Extraction
The soil samples were extracted using acetonitrile and also extraction using
acetonitrile after addition of ammonia were done and the efficiency of the extractions
were assessed. QuEChERS method was adopted for acetonitile extraction of spiked
pesticides from soil. For this purpose, 10 g of air dried, sieved (2 mm) soil was
weighed in a 50 mL centrifuge tube and spiked with the standard insecticide mixture
and evaporated to release the solvent vapours. The soil samples were spiked with
0.05, 0.25 and 0.5 mL each of 10 mg kg-1 solution to get 0.05, 0.25 and 0.5 mg kg-1
levels of each of the spiked compounds. To this, 4 g magnesium sulphate, followed
by 1g sodium chloride and 20 mL acetonitrile were added, shaken for 2 minutes in a
vortex shaker and was centrifuged for 4 minutes at 3300 rpm. A 10 mL supernatant
was transferred to a 15 mL centrifuge tube using a micro pippette and 0.25 g primary
secondary amine and 1.5 g magnesium sulphate were added and was shaken for
30 seconds in vortex followed by centrifugation at 4400 rpm for 10 minutes. After
the centrifugation, 4 mL of the cleaned supernatant extract was transferred to a turbo
26
tube and evaporated to dryness at 40 °C using turboVap. The dry residue was
redissolved in methanol and the volume was made upto 1mL, filtered through 0.22
μm poly vinylidene fluoride (PVDF) syringe filter and passed to a vial which was
wrapped with parafilm to avoid evaporation. In the second method, a slight
modification was tried in the QuEChERS method with addition of 0.5 mL of 10 per
cent ammonia solution after spiking of the pesticide in the soil while all other steps
were same as that of QuEChERS method.
3.2.5.2 Estimation
The cleaned extracts were analyzed on a Liquid Chromatograph equipped
with Triple Quadrupole Mass Spectrometer (Sciex – API 3200). The samples as well
as the standards were injected to the equipment.
3.2.5.2.1 LC- MS System
The ACQUITY ultra performance LC system was used for chromatographic
separation with a column size of 5 µm particle size placed in a column oven at 40 °C.
Elution was done using two elutents (solvent mixtures), viz.,
A: 10 per cent methanol in water + 0.1 per cent formic acid + 50 mM ammonium
acetate
B: 10 per cent water in methanol + 0.1 per cent formic acid + 50 mM Ammonium
acetate.
The flow rate remained constant at 0.8 mL min-1 and the injection volume was 10
µL.
Then the effluent from LC was introduced into triple quadrupole API 3200
MS/MS system. It contains ion source gas 1 (at 50 psi), ion source gas 2 (at 40 psi)
and curtain gas (at 30 psi) with ion source temperature, 550 °C and ion spray voltage
source of 5000 V. The residues were quantified in MS/MS system. For each analyte,
27
two Multiple Reaction Monitoring (MRM) transitions were taken. The other
compound dependent parameters used were shown in Table 5.
Table 5. Multiple- reaction monitoring (MRM) and Liquid Chromatography (LC)
parameters for carbosulfan and its metabolites.
* DP- Declustering Potential, EP- Entrance Potential, CEP- Collision Cell Entrance
Potential, CE -Collision energy, CXP- Collision cell Exit Potential.
3.2.5.3 Residue Quantification and Recovery Experiment
Pesticide residues in the sample (mg kg-1) =
Peak area of sample x Concentration of standard injected x Dilution factor
Peak area of standard
Dilution Factor (DF) = Volume of solvent added x Final volume of the extract
Weight of sample (g) x volume of extract taken for concentration
Sl
No
Compound Retention
time (min)
Precursor
ion Q1 mass
(Da)
Precursor
ion Q2
mass (Da)
DP CEP CE CXP
1 Carbosulfan 5.52
5.52
381.2
381.2
118.1
160.1
42
42
31
31
33
22
1
1
2 Carbofuran 2.21
2.20
222.1
222.1
165.2
123.0
30
30
16.04
26.36
17
29
2
2
3 3-OH
Carbofuran
1.28
1.28
238.1
238.1
181.1
163.1
28
28
24
24
16
21
1
1
4 3-Keto
Carbofuran
1.78
1.79
236.1
236.1
179.1
151.1
33
33
22
23
18
18
1
1
28
Percentage recovery (%) = Concentration of pesticide residue obtained x100
Concentration of pesticide residue added.
Relative standard Deviation (RSD) = Standard deviation x 100
Mean Recovery
A method with Recovery percentage in a range of 80-120 and the Relative Standard
Deviation (RSD) value < 20 will be selected for the study. Limit of quantification
(LOQ) was 0.01 mg kg-1. Limit of Detection (LOD) was 0.005 mg kg-1. The
concentration of carbosulfan and its metabolites in the samples were derived from the
calibration curve and chromatogram of the standards of these compounds. These
calibration curve and chromatograms are appended from I- V.
3.3 MOBILITY OF CARBOSULFAN IN SOILS
The mobility of carbosulfan in the two soil columns were assessed by
analyzing the residues at different depths after loading 3 levels of carbosulfan and
subsequent elution with different levels of water as detailed below.
3.3.1 Technical Programme
Design- CRD
Treatment -12 (3 levels of pesticide and 4 levels of water)
Replication-3
Treatments-
T1-100 µg level of carbosulfan EC + 20 mL water
T2-100 µg level of carbosulfan EC + 40 mL water
T3-100 µg level of carbosulfan EC + 80 mL water
29
T4-100 µg level of carbosulfan EC + 160 mL water
T5-150 µg level of carbosulfan EC + 20 mL water
T6-150 µg level of carbosulfan EC + 40 mL water
T7-150 µg level of carbosulfan EC + 80 mL water
T8-150 µg level of carbosulfan EC + 160 mL water
T9-200 µg level of carbosulfan EC + 20 mL water
T10-200 µg level of carbosulfan EC + 40 mL water
T11-200 µg level of carbosulfan EC + 80 mL water
T12-200 µg level of carbosulfan EC + 160 mL water
Studies on the mobility of carbosulfan was done by using packed soil column
method by loading the given formulation so as to give 100, 150 and 200 µg of
carbosulfan on top of the preloaded column, followed by leaching with measured
amount of water. A laterite soil sample of 191 g and 183 g of coastal alluvial soil
were packed in the PVC columns of height 50 cm and 2.5 cm inner diameter to a
height of 25 cm maintaining the bulk density, simulating field compaction level and
were fixed firmly to burette stands. The lower end of the columns were firmly
fastened by using muslin cloth so as to retain the soil as per the desired bulk density.
The lower end of the soil column was immersed to a conical flask containing water
for 12 h for saturation. On the next day, the saturated soil column was top loaded
with 5 g soil to which required quantity of carbosulfan was added to get 100, 150 and
200 µg level and kept immersed in dry conical flask for collecting the leachate. The
columns were eluted by controlled addition of water at 20 mL, 40 mL, 80 mL and
160 mL, respectively, using drip system at a steady flow in accordance with the
hydraulic conductivity of the soils viz., 0.4 mL min-1 for laterite and 0.6 mL min-1 for
30
Plate 1. Saturation of the soil column for mobility study
Plate 2. Eluting the soil column after treatment
Plate 3. Cut pieces of soil column for residue analysis
coastal alluvial soil obtained from the analysis. The water used for elution
correspond to 50, 100,200 and 400 mm rainfall in field condition and can be used for
prediction of relative mobility along with water under field situation. The leachates
obtained were collected in the conical flasks kept under the soil column. After the
leaching was completed, the leachate as well as the soil were analyzed for residues.
For the soil sample analysis, the pipes / soil columns were cut into 5 portions of 5 cm
each viz., 0-5 cm, 5-10 cm, 10-15 cm, 15-20 cm and 20-25 cm and the residues
present in each of the vertical soil fractions were extracted and quantified.
3.3.2 Monitoring of Pesticide Residues in Leachate
The leachates were separately collected and from each sample a 20 mL
subsample was transferred to a separatory funnel to which 50 mL distilled water was
added. Then 5 g sodium chloride and 20 mL dichloro methane were added followed
by mechanical shaking to cause layer separation and the lower layer was collected in
the round bottom flask after passing it through a funnel containing anhydrous sodium
sulphate. The extraction was repeated two more times using 20 and 10 mL of
dichloromethane each time. The collected extracts were concentrated using a flash
evaporator and were made upto 2 mL using methanol and the residues were estimated
with LC-MS/ MS.
3.4 STUDIES ON THE PERSISTENCE OF CARBOSULFAN IN SOIL
Studies on the persistence of carbosulfan in the two soils viz., laterite and
coastal alluvial were done using EC and granule formulation at three levels (1, 2.5
and 5 mg kg-1) in the laboratory as well as in the field in cropped situation using chilli
(Uujwala) as the test crop. The commercial formulation of carbosulfan (Marshal
25EC and Sheriff 6G) manufactured by FMC was purchased from local market. The
experiment was planned as per the following statistical design.
31
3.4.1 Technical Programme
Design- CRD
Treatments -3
Replication-5
Treatments
T1-Fortification with 1 mg kg-1 carbosulfan formulation
T2- Fortification with 2.5 mg kg-1 carbosulfan formulation
T3- Fortification with 5 mg kg-1 carbosulfan formulation
For conducting the laboratory study, one kg soils each were brought to field
capacity level by adding measured quantity of distilled water (90 mL kg-1 of laterite
and 70 mL kg-1 for coastal alluvial) in the conical flask and spiked separately at 1,2.5
and 5 mg kg-1 levels of carbosulfan using the two formulations, homogenized and
kept aside for 2 hours (0th day). A 10 g soil was taken from the conical flask in
triplicate and analyzed for the residue estimation. Likewise samples were drawn on
1st, 3rd , 5th,7th,10th, 15th , 20th and 30th day for analysis of residues and to identify the
metabolites formed .
In the field condition, chilli crop (variety Ujwala) was raised in the grow bag
as per package of practices recommendation. When the plants were in the flowering
stage, the soils were spiked using the two formulations of carbosulfan at 1, 2.5 and 5
mg kg-1 levels maintaining the moisture at field capacity. The sample analysis were
done on 0, 1, 3, 5, 7, 10, 15, 20, and 30th day as in the case of laboratory study. The
levels of carbosulfan persisting at different time intervals were recorded from which
half life value was calculated.
32
Plate 4. Persistence study under cropped condition
Plate 5. Persistence study under laboratory condition
3.4.2 Calculation of Half Life Period
Theoretically, the pesticide residue should decrease logarithmically with time
since amount lost per unit time should be proportional to the total present at anytime
because all were exposed equally to weathering and degradation (Hoskins, 1981). A
graph should be plotted with time (t) against log of residue parameters (log D), ‘D’
indicates residue in ppm. The graph shows a linear trend which indicates that log D
can be represented as a linear function of ‘ t’ (in days or weeks). The model is,
D =k1E+logk2, that means D = k2 where k2 represent initial deposits. The time
required to reduce D to D/2 is defined as half life so it is calculated as t1/2= log2 / k1
3.5 STUDIES ON THE DEGRADATION OF CARBOSULFAN IN SOIL
Studies on the degradation of carbosulfan were done by analyzing the level of
carbosulfan at different time intervals along with the formation of metabolites such as
carbofuran, 3- hydroxy carbofuran and 3-keto carbofuran in the soil from the parent
compound. The disappearance and corresponding appearance of different metabolites
formed is helpful in studying the chemo-dynamics of carbosulfan in the soils and
thereby arriving at the relative persistence/ stability of carbosulfan in the respective
soils under study.
3.6 EFFECT OF CARBOSULFAN ON MICROBIAL POPULATION
3.6.1 Soil Sampling
A representative area of each of the soil under study was selected from which
an area of 1 m2 was earmarked for treatment application. The required number of
plots to suit the statistical design for collection of the soil from each of the treatment
at two levels were selected. Sufficient space was provided between plots to avoid
cross contamination. Control plots were applied with water and the other plots were
33
applied with granular and EC formulations of carbosulfan at two levels, each in three
replicates.
Soil samples (1 kg) were taken from each of the treatments, combined,
homogenized and sub sample was taken for enumeration of macro and
microorganisms prior to treatment application with the granule and EC formulations
of carbosulfan. Soil samples of 1 kg each were treated with the two formulations of
carbosulfan each at two concentrations 2 hours before treatment and post treatment
samples were taken after 24 hrs of treatment with carbosulfan at 250 g ai ha-1 and
500 g ai ha-1 of formulation at 0-15 cm depth, from which sub samples were taken for
enumeration of soil organisms in treated samples.
3.6.2 Enumeration of Bacteria, Fungi and Actinomycetes
Enumeration of bacteria, fungi and actinomycetes were done by serial dilution
technique (Johnson and Curl, 1972) and then inoculation of the diluted solutions to
respected media under asceptic condition in the laminar airflow chamber and the
plates were incubated at 20°C for the multiplication of the organisms and the colony
formed were counted using a colony counter.
3.6.2.1 Preparation of Media
The media used for enumeration of bacteria, fungi and actinomycetes are
different. Specific media like Potato Dextrose Agar is used for enumeration of fungi
while tryptone soya agar is used for bacteria and casein agar is used for
enumeration of actinomycetes.
3.6.3 Enumeration of Soil Arthropods
The population of macro arthropods in the two soils were assessed by
counting their number in one kg soil by spreading it into a thin layer.
34
Plate 6. Enumeration of soil bacteria
Plate 7. Enumeration of soil fungi
Plate 8. Enumeration of actinomycetes
Plate 9. Enumeration of soil arthropods
For counting the micro arthropods like collembolan and mites, Berlese -
Tullgren funnel method (Macfadyen, 1961) was adopted. For this, 250 g soil
alongwith litter was taken, and with minimum disturbance it was placed on a wire
gauge over a steep slanting funnel. At the lower end of the funnel, a beaker
containing 100 mL of a mixture of ethanol : water in the proportion 75 : 25 was
placed. The upper portion of the funnel was heated gently using a 40W electric bulb
for a period of 24 hrs. Then the arthropods in the soil migrate gently from the heated
upper portion of the soil to lower layers from where it will be collected in the beaker
placed at the tip of the funnel. After 24 hrs, 5 mL of the solution mixture was
transferred to a petri -plate and the number of arthropods were counted under a
binocular microscope. The number of arthropods thus obtained can be used to get the
number of arthropods in 1 kg soil .
3.7 STATISTICAL ANALYSIS
The data generated was statistically analyzed using analysis of variance
(Gomez and Gomez, 1984) and from the dissipation data half life of carbosulfan was
worked out using Hoskins formula (Hoskins, 1981).
35
Results
4. RESULTS
The results of the study entitled ‘Persistence and transformation of
carbosulfan in laterite and coastal alluvium soils of Kerala and its effect on soil
organisms’ are presented under the following headings.
4.1 PHYSICO- CHEMICAL ANALYSIS OF SOILS
Physical and chemical characters of the two soils used for the study were
analyzed as per standard procedures and the results obtained are presented in Tables 6
and 7.
4.1.1 Physico - Chemical Properties of Laterite and Coastal Alluvial Soils
The results of physico- chemical analysis of the two soils were presented in
Tables 6-7. Among the two soils selected, one was sandy loam and the other was
loamy sand in texture. The porosity of coastal alluvial soil is comparatively lesser
than the laterite soil. Water holding capacity and field moisture level of laterite soil is
higher compared to coastal alluvial soil. The particle density and bulk density of the
laterite soils were 2.63 and 1.6 Mg m-3 respecively and for coastal alluvial soil it was
2.56 and 1.58 Mg m-3. The pH of the soils were 5.3 and 5.08 and hence both are
strongly acidic in nature. The EC of the soils were also 0.63 and 0.77 dS m-1. The
cation exchange capacity was more for coastal alluvial amounting to 5.18 c mol kg-1
soil while it was 3.08 cmol kg-1 for laterite soil. The organic matter content and
nutrient contents of coastal alluvial soil was higher than that of the laterite soil. The
organic matter contents of coastal alluvial soil and laterite soils was 0.41 and 0.84
per cent respectively. The status of primary and secondary nutrients were relatively
low for coastal alluvial soil.
36
Table 6. Physico-chemical properties of laterite soil
Sl No. Parameters Results
1 Texture Sandy Loam
2 Sand 61.24 %
3 Silt 27.20 %
4 Clay 11.56 %
5 Bulk density 1.60 Mg m-3
6 Particle density 2.63 Mg m-3
7 Porosity 40.68 %
8 Field Moisture 10.75 %
9 Water Holding Capacity (WHC) 14.09 %
10 pH 5.08
11 Electrical Conductivity (EC) 0.63 dSm-1
12 Cation Exchange Capacity (CEC) 3.08 cmol 100g-1
13 Organic Matter (OM) 0.41 %
14 Available Nitrogen 175.6 kg ha-1
15 Available Phosphorus 22.4 kg ha-1
16 Available Potassium 156.8 kg ha-1
17 Exchangeable Calcium 0.02 meq 100g-1
18 Exchangeable Magnesium 0.03 meq 100g-1
19 Exchangeable Sulphur 4 mg kg-1
37
Table 7. Physico-chemical characters of coastal alluvial soil
Sl No. Parameters Results
1 Texture Loamy Sand
2 Sand 80.68 %
3 Silt 8.48 %
4 Clay 10.84 %
5 Bulk density 1.58 Mg m-3
6 Particle density 2.56 Mg m-3
7 Porosity 38.28 %
8 Field Moisture 7.03 %
9 pH 5.18
10 Electrical Conductivity (EC) 0.77 dSm-1
11 Water Holding Capacity (WHC) 13.18 %
12 Cation Exchange Capacity (CEC) 5.18 cmol kg-1
13 Organic Matter (OM) 0.84 %
14 Available Nitrogen 263.42 kg ha-1
15 Available Phosphorus 28 kg ha-1
16 Available Potassium 264.40 kg ha-1
17 Exchangeable Calcium 0.03 meq 100g-1
18 Exchangeable Magnesium 0.04 meq100g-1
19 Exchangeable Sulphur 6 mg kg-1
38
4.2 MULTI RESIDUE METHODVALIDATION IN SOIL
The method validation for extraction of carbosulfan and its metabolites from
soil were done by spiking with the respective standards so as to obtain a
concentration of 0.05, 0.25 and 0.5 mg kg-1 followed by extraction using acetonitrile
and the residue estimated at different concentrations in the soil are given in the
following Tables 8-13.
4.2.1 Mean Recovery of Carbosulfan and its Metabolites in Laterite Soil
The mean recovery percentage at 0.05 mg kg-1 level of fortification for
carbosulfan and its metabolites in laterite soil ranged from 87-95 per cent (Table 8).
For 3-hydroxy carbofuran, the highest recovery is obtained (95%). The Relative
Standard Deviation (RSD) values obtained ranged from 7.5 to 12.2, and the standard
deviation was from 6.6-11.5 per cent. So for all these compounds, the recovery
percentage obtained were within the satisfactory range (80-120%) and the RSD
values obtained were also in the satisfactory range (< 20) for all the spiked
compounds, and the method is found suitable at 0.05 mg kg-1.
The mean recovery percentage at 0.25 mg kg-1 level of fortification of the
compounds in laterite soil ranged from 90.9 - 98.3 per cent (Table 9). The highest
recovery per centage is obtained for carbofuran which is 98.3 per cent. The RSD
calculated ranged from 7.9-10.5 per cent. The standard deviation ranged from 7.2 -
10.3 per cent. Since all the parameters obtained for this level of fortification is within
the satisfactory range, the method is suitable for adoption in the studies.
The mean recovery per centage of various compounds spiked at 0.5 mg kg-1 in
laterite soil ranged from 94.8-99.2 per cent (Table 10). The highest recovery per
centage was obtained for 3-hydroxy carbofuran. Lowest recovery per centage was
obtained for 3-keto carbofuran. For carbosulfan, the recovery per centage was 97.2
39
Table 8. Mean recovery of carbosulfan and its metabolites when spiked at 0.05 mg
kg-1 level in laterite soil
Mean of six replications
Table 9. Mean recovery of carbosulfan and its metabolites when spiked at 0.25 mg
kg-1 level in laterite soil
Mean of six replications
Table 10. Mean recovery of carbosulfan and its metabolites when spiked at 0.50 mg
kg-1 level in laterite soil
Mean of six replications
Compound Recovery Percentage Standard Deviation Relative Standard
Deviation (RSD)
Carbosulfan 94.00 9.31 9.91
Carbofuran 92.80 8.61 9.20
3-hydroxy carbofuran 95.00 11.50 12.20
3-keto carbofuran 87.00 6.60 7.50
Compound Recovery Percentage Standard Deviation Relative Standard
Deviation (RSD)
Carbosulfan 90.90 7.20 7.90
Carbofuran 98.30 10.30 10.50
3-hydroxy carbofuran 96.60 8.50 8.80
3-keto carbofuran 95.40 7.80 8.20
Compound Recovery Percentage Standard Deviation Relative Standard
Deviation (RSD)
Carbosulfan 97.20 9.30 9.50
Carbofuran 95.20 8.60 9.00
3-hydroxy carbofuran 99.20 11.50 11.60
3-keto carbofuran 94.80 6.60 6.90
40
Table 11. Mean recovery of carbosulfan and its metabolites when spiked at 0.05 mg
kg-1 level in coastal alluvial soil
Mean of six replications
Table 12. Mean recovery of carbosulfan and its metabolites when spiked at 0.25 mg
kg-1 level in Coastal Alluvial soil
Mean of six replications
Table 13. Mean recovery of carbosulfan and its metabolites when spiked at 0.50 mg
kg-1 level in coastal alluvial soil
Mean of six replications
Compound Recovery Percentage Standard Deviation Relative Standard
Deviation (RSD)
Carbosulfan 91.00 7.20 7.80
Carbofuran 88.40 4.10 4.60
3-hydroxy carbofuran 89.00 4.10 4.70
3-keto carbofuran 92.00 8.20 8.90
Compound Recovery Percentage Standard Deviation Relative Standard
Deviation (RSD)
Carbosulfan 92.00 5.70 6.10
Carbofuran 94.30 7.60 8.10
3-hydroxy carbofuran 100.60 9.10 9.00
3-keto carbofuran 96.00 8.30 8.70
Compound Recovery Percentage Standard Deviation Relative Standard
Deviation (RSD)
carbosulfan 96.40 7.30 7.40
Carbofuran 90.80 4.10 4.50
3-hydroxy
carbofuran 90.40 4.10 4.60
3-keto carbofuran 97.60 8.40 8.40
41
per cent. The RSD values ranged from 6.9-11.6 per cent and the standard deviation
ranged from 6.6-11.5 per cent.
4.2.2 Mean Recovery of Carbosulfan and its Metabolites in Coastal Alluvial Soil
The mean recovery percentage of carbosulfan and its metabolites spiked at
0.05 mg kg-1 in coastal alluvial ranged from 88.4-92 per cent (Table 11). The RSD
value ranged from 4.6-8.9 and standard deviation ranged from 4.1-8.2 per cent. The
highest recovery was obtained for 3-keto carbofuran. For carbofuran and 3-hydroxy
carbofuran, same RSD values were obtained.
From Table 12, the recovery percentage for the compounds spiked at 0.25 mg
kg-1 in coastal alluvial soil ranged from 92.00 - 100.60 per cent. The highest recovery
percentage at this concentration was for 3-hydroxy carbofuran and the lowest was for
carbosulfan. The RSD values ranged from 6.1-9. Per cent and the standard deviation
ranged from 5.70 - 9.10 per cent.
From Table 13, the recovery percentage of carbosulfan and its metabolites at
0.5mg kg-1 level of fortification in coastal alluvial soil ranged from 90.40 - 97.60.
Here carbofuran and 3-hydroxy carbofuran had almost similar recovery percentage, ie
values 90.80 and 90.40 per cent respectively. The RSD value obtained were in the
range of 4.50-8.40 and the standard deviation ranged from 4.10 - 8.40. The
chromatogram, calibration curve and mass spectra of the standards and recovery
experiments are appended in appendix 1 to V.
4.3 MOBILITY OF CARBOSULFAN IN SOIL
The mobility of carbosulfan was determined by analyzing the residue found at
different depths of the two soil columns through which definite concentration of the
pesticides (100, 150 and 200 µg) was allowed to elute by application of definite
42
volume of water (20, 40, 80 and 160 mL) to the column. The results obtained were
given in the following tables.
4.3.1 Mobility of Carbosulfan and Carbofuran in Laterite Soil
Data on the downward migration of carbosulfan 25 EC by application at 100
µg in laterite soil when eluted with 20, 40, 80 and 160 mL of water are presented in
Table 14. The data revealed that, when 20 mL water was added, carbosulfan moved
upto 10 cm depth and majority of carbosulfan residues (1.503 mg kg-1) were confined
to the top 0-5 cm layer of soil. When the water used for elution increased to 40 mL,
the migration was detected upto 15 cm and the quantity of carbosulfan in the top
layer was reduced (0.011 mg kg-1). When the water for elution was 160 mL, more
migration was noticed and a further decrease in the concentration of carbosulfan was
noticed at top 0- 5 cm, indicating a more migration of carbosulfan with increase in
volume of water for elution.
Data regarding the downward movement of carbofuran detected in soil by
addition of carbosulfan 25 EC at 100 µg in laterite soil was presented in Table. 15.
The data revealed that, when 20 mL water was used for elution, the residue obtained
at 0-5 cm was 0.353 mg kg-1. With increase in the volume of water to 160 mL, there
is lower retention of carbofuran at 0-5 cm layer and the migration was noticed upto
15 cm.
Data on the downward migration of carbosulfan 25 EC with application at 150 µg in
laterite soil when eluted with 20, 40, 80 and 160 mL of water is presented in Table
16. The data revealed that, when 20 mL water was added, carbosulfan moved upto
10 cm depth and majority of carbosulfan residues (2.293 mg kg-1) were confined to
the top 0-5 cm layer of soil. When the water used for elution increased to 40 mL, the
migration was detected upto 15 cm and the quantity of carbosulfan in the top layer
was reduced (1.810 mg kg-1). When the water for elution was 160 mL,
43
Table 14. Migration of carbosulfan in laterite soil column when loaded at100 µg level
Mean of three replications
Table 15. Migration of carbofuran formed in laterite soil column when loaded with
100 µg carbosulfan
Mean of three replications *BDL- Below Detectable Level (0.01 mg kg-1)
Depth of soil column/
Leachate
Residues ( mg kg-1) at different depths
20 mL 40 mL 80 mL 160 mL
0-5cm 1.503 1.043 0.364 0.044
5-10cm 0.016 0.045 0.032 0.283
10-15cm BDL 0.011 0.015 0.026
15-20cm BDL BDL BDL BDL
20-25cm BDL BDL BDL BDL
Leachate BDL BDL BDL BDL
Depth of soil column/
Leachate
Residues ( mg kg-1) at different depths
20 mL 40 mL 80 mL 160 mL
0-5cm 0.353 0.241 0.117 0.015
5-10cm BDL BDL 0.013 0.053
10-15cm BDL BDL BDL 0.012
15-20cm BDL BDL BDL BDL
20-25cm BDL BDL BDL BDL
Leachate BDL BDL BDL BDL
44
Table 16. Migration of carbosulfan in laterite soil column when loaded at 150 µg level
Mean of three replications Table 17. Migration of carbofuran formed in laterite soil column when loaded with 150 µg carbosulfan
Mean of three replications *BDL- Below Detectable Level (0.01 mg kg-1)
Depth of
soil column/ Leachate
Residues ( mg kg-1) at different depths
20 mL 40 mL 80 mL 160 mL
0-5cm 2.293 1.810 0.762 0.267
5-10cm 0.029 0.067 0.166 0.573
10-15cm BDL 0.014 0.036 0.041
15-20cm BDL BDL 0.012 0.020
20-25cm BDL BDL BDL BDL
Leachate BDL BDL BDL BDL
Depth of
soil column/ Leachate
Residues ( mg kg-1) at different depths
20 mL 40 mL 80 mL 160 mL
0-5cm 0.572 0.432 0.153 0.082
5-10cm 0.011 0.020 0.032 0.104
10-15cm BDL BDL 0.020 0.079
15-20cm BDL BDL BDL BDL
20-25cm BDL BDL BDL BDL
Leachate BDL BDL BDL BDL
45
Table 18. Migration of carbosulfan in the laterite soil column when loaded at 200 µg level
Mean of three replications
Table 19. Migration of carbofuran formed in laterite soil column when loaded with 200 µg carbosulfan
Mean of three replications *BDL- Below Detectable Level (0.01 mg kg-1
Depth of
soil column/ Leachate
Residues ( mg kg-1) at different depths
20 mL 40 mL 80 mL 160 mL
0-5cm 3.553 2.437 1.303 0.049
5-10cm 0.065 0.193 0.364 0.383
10-15cm 0.011 0.015 0.130 0.026
15-20cm BDL BDL 0.012 0.020
20-25cm BDL BDL BDL 0.019
Leachate BDL BDL BDL 0.013
Depth of soil
column/ Leachate
Residues ( mg kg-1) at different depths
20 mL 40 mL 80 mL 160 mL
0-5cm 0.724 0.511 0.294 0.002
5-10cm BDL 0.031 0.081 0.102
10-15cm BDL BDL 0.014 0.035
15-20cm BDL BDL BDL 0.012
20-25cm BDL BDL BDL BDL
Leachate BDL BDL BDL BDL
46
more migration was noticed upto 20 cm and a further decrease in the concentration of
carbosulfan was noticed at top 0- 5 cm, indicates more migration of carbosulfan with
increased volume of water for elution.
Data regarding the downward movement of carbofuran by adding carbosulfan
25 EC at 150 µg in laterite soil was presented in Table 17. The data revealed that
when 20 mL water was used for elution, the residue obtained at 0-5 cm was 0.572 mg
kg-1. With increase in the volume of water to 160 mL there is lower retention of
carbofuran at 0- 5 cm layer and the migration was noticed upto 15 cm.
Data on the downward migration of carbosulfan 25 EC by application at 200
µg in laterite soil when eluted with 20, 40, 80 and 160 mL of water are presented in
Table 18. The data revealed that, when 20 mL water added, carbosulfan was moved
upto 15 cm depth and majority of carbosulfan residues (3.553 mg kg-1) confined to
the top 0-5cm layer of soil. When the water used for elution increased to 80 mL, the
migration was detected upto 20 cm and the quantity of carbosulfan in the top layer
was reduced (1.303 mg kg-1). When the water for elution was 160 mL, more
migration was noticed upto 25 cm and a further decrease in the concentration of
carbosulfan was noticed at top 0-5 cm. The leachate also had the residues of
carbofuran (0.013 mg kg-1) indicating more migration of carbosulfan with increased
volume of water for elution.
Data regarding the downward movement of carbofuran by adding carbosulfan
25 EC at 200 µg in laterite soil was presented in Table 19. The data revealed that,
when 20 mL water was used for elution, the residue obtained at 0-5 cm was 0.724 mg
kg-1, and with increasing the volume of water to 160 mL there was lower retention of
carbofuran at 0- 5 cm layer and the migration was noticed upto 20 cm. The leachate
did not show any detectable residues of carbofuran.
47
4.3.2 Mobility of Carbosulfan and Carbofuran in Coastal Alluvial Soil
Data on the downward migration of carbosulfan 25 EC by application at 100
µg in coastal alluvial soil when eluted with 20, 40, 80 and 160 mL of water is
presented in Table 20. The data revealed that, when 20 mL water was added
carbosulfan was moved upto 15 cm depth and majority of carbosulfan residues (1.783
mg kg-1) were confined to the top 0-5cm layer of soil. When the water used for
elution increased to 80 mL, the migration was detected upto 20 cm and the quantity
of carbosulfan in the top layer was reduced (0.616 mg kg-1). When the water for
elution was 160 mL more migration was noticed upto 25 cm and a further decrease
in the concentration of carbosulfan was noticed at top 0-5 cm ( 0.319 mg kg-1). The
leachate showed no residues of carbofuran, even with an increased volume of water
used for elution.
Data regarding the downward movement of carbofuran by adding carbosulfan
25 EC at 100 µg in coastal alluvial soil was presented in Table 21. The data revealed
that, when 20 mL water used for elution the residue obtained at 0-5 cm was 0.212 mg
kg-1. With increase in the volume of water to 160 mL, there was a lower retention of
carbofuran at 0-5 cm layer (0.042 mg kg-1) and the migration was noticed upto 15 cm.
The leachate did not show any carbofuran residues.
Data on the downward migration of carbosulfan 25 EC by application at 150
µg in coastal alluvial soil when eluted with 20, 40, 80 and 160 mL of water is
presented in Table 22. The data revealed that, when 20 mL water added, carbosulfan
was moved upto 15 cm depth and majority of carbosulfan residues (2.201 mg kg-1)
confined to the top 0-5cm layer of soil. When the water used for elution increased to
80 mL, the migration was detected upto 20 cm and the quantity of carbosulfan in the
top layer was reduced (0.928 mg kg-1). When the water for elution was 160 mL,
more migration was noticed upto 25 cm and a further decrease in the concentration of
carbosulfan was noticed at top 0- 5 cm and that was 0.509 mg kg-1.
48
Table 20. Migration of carbosulfan in the coastal alluvial soil column when loaded at
100 µg level
Mean of three replications
Table 21. Migration of carbofuran formed in coastal alluvial soil column when loaded with 100 µg carbosulfan
Mean of three replications *BDL- Below Detectable Level (0.01 mg kg-1)
Depth of soil column/
Leachate
Residues ( mg kg-1 ) at different depths
20 mL 40 mL 80 mL 160 mL
0-5cm 1.783 1.038 0.616 0.319
5-10cm 0.243 0.418 0.506 0.484
10-15cm 0.012 0.037 0.085 0.118
15-20cm BDL BDL 0.021 0.033
20-25cm BDL BDL BDL BDL
Leachate BDL BDL BDL BDL
Depth of soil
column/ Leachate
Residues ( mg kg-1 ) at different depths
20 mL 40 mL 80 mL 160 mL
0-5cm 0.212 0.152 0.093 0.042
5-10cm 0.091 0.047 0.076 0.056
10-15cm BDL BDL 0.014 0.025
15-20cm BDL BDL BDL BDL
20-25cm BDL BDL BDL BDL
Leachate BDL BDL BDL BDL
49
Table 22. Migration of carbosulfan in the coastal alluvial soil column when loaded at
150 µg level
Mean of three replications
Table 23. Migration of carbofuran formed in laterite soil column when loaded with 150 µg carbosulfan
Mean of three replications *BDL- Below Detectable Level (0.01 mg kg-1)
Depth of soil column/ Leachate
Residues ( mg kg-1) at different depths
20 mL 40 mL 80 mL 160 mL
0-5cm 2.201 1.806 0.928 0.509
5-10cm 0.320 0.521 0.770 0.416
10-15cm 0.014 0.047 0.103 0.201
15-20cm BDL BDL 0.048 0.016
20-25cm BDL BDL BDL 0.011
Leachate BDL BDL BDL BDL
Depth of soil column/
Leachate
Residues ( mg kg-1) at different depths
20 mL 40 mL 80 mL 160 mL
0-5cm 0.322 0.211 0.108 0.083
5-10cm 0.039 0.044 0.059 0.091
10-15cm 0.011 0.003 0.024 0.035
15-20cm BDL BDL 0.014 0.021
20-25cm BDL BDL BDL BDL
Leachate BDL BDL BDL BDL
50
Table 24. Migration of carbosulfan in the coastal alluvial soil column when loaded at 200 µg level
Mean of three replications Table 25. Migration of carbofuran formed in coastal alluvial soil column when loaded with
200 µg carbosulfan
Mean of three replications *BDL- Below Detectable Level (0.01 mg kg-1)
Depth of soil column/
Leachate
Residues ( mg kg-1) at different depths
20 mL 40 mL 80 mL 160 mL
0-5cm 3.073 2.563 1.583 0.718
5-10cm 0.420 0.712 0.495 0.684
10-15cm 0.106 0.079 0.260 0.414
15-20cm BDL 0.029 0.166 0.139
20-25cm BDL 0.014 0.050 0.094
Leachate BDL BDL 0.016 0.030
Depth of soil column/
Leachate
Residues ( mg kg-1) at different depths
20 mL 40 mL 80 mL 160 mL
0-5cm 0.523 0.359 0.141 0.091
5-10cm 0.057 0.116 0.086 0.077
10-15cm BDL 0.01 0.044 0.048
15-20cm BDL BDL 0.014 0.020
20-25cm BDL BDL BDL BDL
Leachate BDL BDL BDL BDL
51
Data regarding the downward movement of carbofuran by adding carbosulfan
25 EC at 150 µg in coastal alluvial soil was presented in Table 23. The data revealed
that when 20 mL water was used for elution the residue obtained at 0-5 cm was 0.322
mg kg-1. With increase in the volume of water to 160 mL, there was a lower retention
of carbofuran at 0- 20 cm layer and the migration was noticed upto 20 cm. The
leachate did not show the carbofuran residues.
Data on the downward migration of carbosulfan 25 EC by application at 200
µg in coastal alluvial soil when eluted with 20, 40, 80 and 160 mL of water is
presented in Table 24. The data revealed that, when 20 mL water was added,
carbosulfan moved upto 15 cm depth and majority of carbosulfan residues (3.073 mg
kg-1) confined to the top 0-5cm layer of soil. When the water used for elution
increased to 40 mL, the migration was detected upto 25 cm, and the quantity of
carbosulfan in the top layer was reduced (2.563 mg kg-1). When the water for elution
was 160 mL, more migration was noticed upto 25 cm and a further decrease in the
concentration of carbosulfan was noticed at top 0- 5 cm and that was 0.718 mg kg-1.
The leachate had a residue content of 0.030 mg kg-1 .
Data regarding the downward movement of carbofuran by adding carbosulfan
25 EC at 200 µg in coastal alluvial soil was presented in Table 25. The data revealed
that when 20 mL water was used for elution, the residue obtained at 0-5 cm was
0.523 mg kg-1. With increase in the volume of water to 160 mL, there was a lower
retention of carbofuran at 0- 20 cm layer and the migration was noticed upto 20 cm.
The leachate did not show the carbofuran residues.
4.4 PERSISTENCE OF CARBOSULFAN IN SOIL
The persistence of carbosulfan in the laterite as well as in the coastal alluvial
soil were studied at three levels of carbosulfan viz., 1, 2.5 and 5 mg kg-1 using EC as
well as granular (G) formulation under laboratory condition as well as in the cropped
52
condition. The half life of the compounds at different treatment levels and
formulation under the above two situations were also found out after quantifying the
residue level in the soil on the 0th, 1st, 3rd, 5th, 7th, 10th, 15th, 20th and 30th day. The
results obtained are given in the following Tables 26- 29.
4.4.1 Dissipation of Carbosulfan 25EC in Laterite Soil under Laboratory and
Cropped Conditions
The data on the persistence or dissipation of carbosulfan 25EC in laterite soil
under laboratory and cropped conditions are presented in Table 26. The data revealed
that by the application of EC formulations, the concentration of carbosulfan in soil
decreased with time. When the pesticide is applied in the bare soil, the pesticide
remained for upto 30 days, even though its quantity is very less. But in the cropped
condition, it remained only upto 15 days. The half life period of carbosulfan is high
under laboratory study while it was less under cropped condition at all treatment
levels. With higher the treatment concentration, higher the half life. In laboratory
condition at 1 mg kg-1 level, the residues were obtained upto 30th day, on the 0th day,
the residue obtained was 0.834 mg kg-1 while on 30th day it was 0.011 with a
corresponding half life of 5.08 days. For 2.5 and 5 mg kg-1 also, the residues were
obtained upto 30th day. For 2.5 and 5 mg kg-1 treatments, the residues obtained on the
0th day were 2.08 and 4.18 mg kg-1, respectively, and on 30th day that were 0.021 and
0.232 mg kg-1 with corresponding half life of 7.69 and 10.53 days, respectively.
In the cropped condition at 1 mg kg-1 level, the residues were obtained upto 10th day.
On the 0th day, the residue was 0.645 mg kg-1 and that on 10th day was 0.130 with a
corresponding half life of 2.17 days. For 2.5 and 5 mg kg-1 the residues were
obtained upto 15th day. On the 0th day, the residues obtained were 1.792 and 3.71 mg
kg-1 respectively and on 15th day that were 0.176 and 0.435 mg kg-1 with
corresponding half life of 4.60 and 5.24 days respectively. The half life period was
nearly halved in cropped condition than the laboratory condition. So a faster
53
Table 26. Dissipation of carbosulfan 25 EC in laterite soil under laboratory and cropped condition
Treatment
Mean residues of carbosulfan (mg kg-1)
Days after treatment
0 1 3 5 7 10 15 20 30 t1/2
(Days)
T1(1mgkg-1 in
laboratory
condition)
0.834 0.821 0.761 0.651 0.523 0.340 0.232 0.041 0.011 5.080
T2(2.5mg kg-1 in
laboratory
condition)
2.081 1.870 1.392 1.112 0.933 0.872 0.720 0.263 0.021 7.690
T3(5mg kg-1 in
laboratory
condition)
4.182 3.991 3.501 3.081 2.841 2.110 1.793 1.072 0.232 10.530
T4(1mg
kg-1 in cropped
condition)
0.645 0.622 0.598 0.436 0.224 0.130 BDL BDL BDL 2.170
T5(2.5mg kg-1
in cropped
condition)
1.792 1.620 1.320 1.040 0.748 0.542 0.176 BDL BDL 4.600
T6(5mg kg-1 in
cropped
condition)
3.710 3.090 2.961 2.731 2.161 1.470 0.435 BDL BDL 5.240
Mean of five replications
*BDL- Below Detectable Level (0.01 mg kg-1
54
dissipation was observed in the cropped condition compared to the laboratory
condition.
4.4.2 Dissipation of Carbosulfan 25 EC in Coastal Alluvial Soil under
Laboratory and Cropped Conditions
The data regarding dissipation of carbosulfan in coastal alluvial soil by
treating the soil with carbosulfan 25 EC under laboratory and cropped conditions
were presented in Table 27. It is seen that, the residues were decreased from 0th day
to 15th day in laboratory and cropped condition at 1 mg kg-1 while it was 0th to 20th
day for higher level of treatment under cropped condition. The initial recovery of
carbosulfan was higher under laboratory study but at 20th day, the recovery was
higher for cropped condition at 5mg kg-1 level of fortification. In laboratory
condition at 1 mg kg-1 level the residues were obtained upto 15th day, on the 0th day
the residue obtained was 0.727 mg kg-1 while on 15th day, it was 0.012 with a
corresponding half life of 2.35 days. For 2.5 and 5 mg kg-1, the residues were
obtained upto15th and 20th day respectively. On the 0th day, the residues obtained
were 1.59 and 2.43 mg kg-1 respectively and on 15th day that were 0.088 and 0.135
mg kg-1with corresponding half life of 2.91 and 4.96 days respectively.
In the cropped condition at 1 mg kg-1 level, the residues were obtained upto
15th day, on the 0th day, the residue was 0.418 mg kg-1 and that on 10th day was 0.011
with a corresponding half life of 2.95 days. For 2.5 and 5 mg kg-1, the residues were
obtained upto 20th day. On the 0th day the residues obtained were 0.717 and 0.959 mg
kg-1 respectively and on 20th day that were 0.045 and 0.078 mg kg-1 with
corresponding half life of 4.59 and 5.13 days respectively. The half life obtained
were higher for laboratory study than cropped condition. With increasing the
pesticide concentration, the half life was also increased.
55
Table 27. Dissipation of carbosulfan 25 EC in coastal alluvial soil under laboratory and cropped
condition
Treatment
Mean residues of carbosulfan (mg kg-1)
Days after treatment
0 1 3 5 7 10 15 20 30 t1/2
(Days)
T1(1 mg kg-1 in
laboratory
condition) 0.727 0.646 0.448 0.248 0.211 0.115 0.012 BDL BDL 2.350
T2(2.5 mg kg-1 in
laboratory
condition) 1.590 1.071 0.765 0.517 0.417 0.242 0.088 BDL BDL 2.910
T3(5 mg kg-1in
laboratory
condition) 2.431 1.540 1.172 1.010 0.872 0.521 0.216 0.135 BDL 4.960
T4(1 mg kg-1 in
Cropped
condition) 0.418 0.387 0.348 0.276 0.128 0.094 0.011 BDL BDL
2.950
T5(2.5 mg kg-1
in cropped
condition) 0.717 0.672 0.644 0.567 0.333 0.120 0.095 0.045 BDL
4.590
T6(5 mg kg-1in
cropped
condition) 0.959 0.846 0.748 0.673 0.439 0.253 0.118 0.078 BDL
5.130
Mean of five replications *BDL- Below Detectable Level (0.01 mg kg-1)
56
4.4.3 Dissipation of Carbosulfan Granules in the Laterite Soil under
Laboratory and Cropped Conditions
The data regarding the dissipation of carbosulfan in the laterite soil by treating
with carbosulfan granules in the laboratory and cropped conditions are presented in
Table 28. The result revealed that, the residues were increased from 0th – 7th day and
0th -3rd day in the soil under laboratory and cropped condition respectively. For
granular treatments, the higher residue content was observed for cropped condition
than the laboratory condition. In this, except 5mg kg-1 level of treatment, all other got
the residues only upto 15th day and for 5mg kg-1 level, the residues persisted upto 20th
day. In laboratory condition, at 1 mg kg-1 level, the residues obtained upto 15th day.
On the 0th day, the residues obtained were 0.042 mg kg-1 and on 15th day, it was
0.023 mg kg-1 with a corresponding half life of 9.88 days. For 2.5 and 5 mg kg-1, the
residues were obtained upto 15th day. On the 0th day, the residues obtained were
0.246 and 0.725 mg kg-1 respectively. On 15th day, that were 0.113 and 0.442 mg
kg-1 with corresponding half life of 10.50 and 11.50 days, respectively.
In the cropped condition, at 1 mg kg-1 level, the residues were obtained upto
10th day. On the 0th day, the residue was 0.238 mg kg-1 and that on 10th day, was
0.109 mg kg-1 with a corresponding half life of 3.26 days. For 2.5 and 5 mg kg-1, the
residues were obtained upto 15th and 20th days respectively. On the 0th day, the
residues obtained were 0.700 and 1.05 mg kg-1 and that were 0.176 and 0.435 mg kg-1
on 15th and 20th days respectively with corresponding half life of 4.60 and 5.24 days
respectively. The half life was higher for laboratory study than the cropped condition.
4.4.4 Dissipation of Carbosulfan Granules in Coastal Alluvial Soil under
Laboratory and Cropped Conditions
As regards to the dissipation of carbosulfan in coastal alluvial soil by treating
with carbosulfan granules under laboratoryoratory and field conditions are presented
57
Table 28. Dissipation of carbosulfan granules in laterite soil under laboratory and cropped condition
Mean of five replication *BDL- Below Detectable Level (0.01 mg kg-1)
Treatment
Mean residues of carbosulfan (mg kg-1)
Days after treatment
0 1 3 5 7 10 15 20 30 t1/2
(Days)
T1(1 mg kg-1 in
laboratory
condition) 0.042 0.106 0.118 0.135 0.223 0.112 0.023 BDL BDL 9.880
T2(2.5 mg kg-1 in
laboratory
condition) 0.246 0.305 0.431 0.539 0.599 0.274 0.117 BDL BDL 10.500
T3(5 mg kg-1 in
laboratory
condition) 0.725 0.727 0.813 1.050 1.200 0.721 0.455 0.211 BDL 11.500
T4(1 mg
kg-1 in cropped
condition) 0.238 0.297 0.452 0.426 0.249 0.109 BDL BDL BDL
3.260
T5(2.5 mg kg-1
in cropped
condition) 0.700 0.728 0.818 0.663 0.422 0.223 0.113 BDL BDL
5.160
T6(5 mg kg-1 in
cropped
condition) 1.050 1.191 1.582 1.450 1.011 0.702 0.442 0.160 BDL
7.300
58
Table 29. Dissipation of carbosulfan granules in coastal alluvial soil under laboratory and
cropped condition
Mean of five replications
*BDL- Below Detectable Level (0.01 mg kg-1)
Treatment
Mean residues of carbosulfan ( mg kg-1)
Days after treatment
0 1 3 5 7 10 15 20 30 t1/2
(Days)
T1(1 mg kg-1 in
laboratory
condition) 0.094 0.181 0.256 0.143 0.118 0.059 0.011 BDL BDL 8.990
T2(2.5 mg kg-1 in
laboratory
condition) 0.268 0.371 0.570 0.383 0.309 0.217 0.116 BDL BDL 9.450
T3(5 mg kg-1 in
laboratory
condition) 0.405 0.510 1.300 0.717 0.516 0.342 0.222 BDL BDL 10.650
T4(1 mg
kg-1 in cropped
condition) 0.033 0.131 0.211 0.172 0.091 0.061 0.011 BDL BDL
5.700
T5(2.5 mg kg-1
in cropped
condition) 0.611 0.714 0.792 0.665 0.530 0.304 0.141 BDL BDL
6.510
T6(5 mg kg-1 in
cropped
condition) 0.913 0.940 1.09 0.985 0.810 0.622 0.461 0.230 BDL
9.820
59
in Table 29 it is seen that, a higher retention of the residues were obtained in the
cropped condition In laboratory condition at 1 mg kg-1 level, the residues were
obtained upto 15th day. On the 0th day, the residue obtained was 0.094 mg kg-1 while
on 15th day it was 0.011 with a corresponding half life of 8.99 days. For 2.5 and 5 mg
kg-1 the residues were obtained upto15th day. On the 0th day, the residues obtained
were 0.268 and 0.405 mg kg-1 respectively, and on 15th day, that were 0.116 and
0.222 mg kg-1 with corresponding half life of 9.45 and 10.65 days respectively.
In the cropped condition at 1 mg kg-1 level, the residues were obtained upto
15th day. On the 0th day, the residue was 0.033 mg kg-1 and that on 15th day was 0.011
with a corresponding half life of 5.7 days. For 2.5 and 5 mg kg-1, the residues were
obtained upto 15th and 20th days respectively. On the 0th day, the residues obtained
were 0.611 and 0.913 and on 15th and 20th day it was 0.141 and 0.230 mg kg-1 with
corresponding half life of 6.51 and 9.82 days respectively.
4.4.5 Overall Dissipation of Carbosulfan as Influenced by Soil Type,
Formulation, Crop, Treatment Levels and their Combined effects
The data on the overall dissipation of carbosulfan influenced by soil type,
formulation, crop and treatment levels were presented in Table 30. The data revealed
that, in laterite soil, the retention of carbosulfan was comparatively higher than the
coastal alluvial soil. Carbosulfan persisted for more time in laterite soil. The residue
detected on 20th day in laterite soil was 0.13mg kg-1 while that in the coastal alluvial
soil was 0.04 mg kg-1. Thus, a fast degradation of carbosulfan was noticed in coastal
alluvial soil than the laterite soil. The granular formulation shows a residue content
of 0.14 mg kg-1 on 20th day while for EC formulation the residue was 0.03 mg kg-1.
The residue obtained in the laboratory condition was higher than that in the cropped
condition during all the days. On the 20th day, it was 0.13 mg kg-1 under laboratory
condition while it was 0.04 mg kg-1 under cropped condition. The data regarding the
influence of treatment levels on the dissipation of carbosulfan are presented in Table
60
Table 30. Overall dissipation of carbosulfan as influenced by soil, formulation, crop and treatment levels
* S1- Laterite soil, S2- Coastal Alluvial soil, F1- Granules, F2- EC, T1- Laboratory condition, T2- Cropped condition
Treatments* Mean residues of Carbosulfan ( mg kg-1)
Days after treatment
0 1 3 5 7 10 15
20th
day
Factor-1 soils
S1 0.87 1.3 1.36 1.12 0.94 0.66 0.42 0.13
S2 0.75 0.63 0.76 0.51 0.47 0.25 0.16 0.04
Factor-2 Formulations
F1 0.92 1.4 1.67 1.01 0.82 0.57 0.34 0.14
F2 0.69 0.49 0.46 0.62 0.59 0.34 0.24 0.03
Factor-3 Crop
T1 1.01 1.02 1.14 0.79 0.74 0.51 0.35 0.13
T2 0.59 0.9 0.99 0.84 0.67 0.41 0.23 0.04
SE 0.009 0.006 0.008 0.013 0.004 0.006 0.003 0.002
CD 0.026 0.016 0.023 0.035 0.011 0.016 0.008 0.005
61
31. The data revealed that with increased concentration / treatment levels, a
corresponding increase in the residue level was seen.
The influence of different combined effects of soil, formulations and
conditions on the dissipation of carbosulfan are presented in Table 32. The effect of
granule formulation under laterite soil showed higher residues than all other
combined effects. The effect of the two formulations viz., EC and granules under
coastal alluvium soil showed same residues on 20th day. The effect of EC formulation
under laterite soil with showed second most residues on 20th day. The combined
effects S1F2- laterite soil with EC formulation and S2F2- coastal alluvium soil with
EC formulation were on par on 0th day. On 20th day, S2F1 (coastal alluvium soil with
granules) and S2F2 (coastal alluvium soil with EC) were on par and all other
combined effects were significantly different.
The combined effect of soil type and condition / crop showed highest residue
content in the combined effect of laterite soil under laboratory condition on the 20th
day (0.20 mg kg-1). The combined effect of coastal alluvial soil with cropped
situation showed second highest residue of 0.06 mg kg-1. The lowest residue content
was for the combined effect of laterite soil under cropped condition (0.02 mg kg-1).
On 10th day S2T1 (coastal alluvium soil under laboratory condition) and S2T2
(coastal alluvium soil under cropped condition) are showing residue content on par
and all others were significantly different.
The combined effect of formulations and conditions presented in Table 32
revealed that, on the 0th day, the combined effect of EC formulation under laboratory
condition showed maximum residues (1.59 mg kg-1) among all other combined
effects. On the 20th day, the highest residue was obtained for combined effect of
granule formulation under laboratory condition (0.36 mg kg-1). The combined effect
of EC with laboratory condition showed residues to the tune of 0.09 mg kg-1 on 20th
day. The lowest residue content was obtained for combined effect of EC formulation
62
Table 31. Dissipation of carbosulfan as influenced by treatment levels
*P1- 1 mg kg-1, P2- 2.5 mg kg-1, P3- 5 mg kg-1
Treatments*
Residues of carbosulfan ( mg kg-1)
Days after treatment
0 1 3 5
7
10 15 20
P1 0.33 0.41 0.39 0.32 0.34 0.13 0.06 0.01
P2 0.69 0.89 0.99 0.69 0.54 0.36 0.22 0.04
P3 1.39 1.6 1.81 1.4 1.2 0.88 0.59 0.203
SE 0.0114 0.0071 0.0101 0.0154 0.005 0.007 0.0035 0.0023
CD 0.032 0.0197 0.028 0.043 0.013 0.019 0.009 0.0064
63
Table 32. Dissipation of carbosulfan as influenced by interaction of soil, formulations and conditions
*S1- Laterite soil, S2- Coastal Alluvial soil, F1- Granules, F2- EC, T1- Laboratory condition, T2- Cropped condition
Interactions*
Mean residues of Carbosulfan ( mg kg-1)
Days after treatment
0 1 3 5 7 10 15 20
Interaction of soil and formulations
S1F1 1.05 1.19 1.31 0.95 0.73 0.42 0.38 0.24
S1F2 1.69 1.38 0.95 0.65 0.44 0.31 0.24 0.06
S2F1 0.79 0.86 1.14 0.52 0.40 0.22 0.12 0.04
S2F2 1.70 1.41 1.19 0.74 0.38 0.27 0.14 0.04
Interaction of soil and condition
S1T1 1.18 1.30 1.36 1.10 1.07 0.76 0.59 0.20
S1T2 0.96 0.82 0.77 0.69 0.60 0.57 0.26 0.02
S2T1 0.85 0.79 0.72 0.40 0.31 0.25 0.11 0.04
S2T2 0.62 0.55 0.51 0.46 0.44 0.25 0.21 0.06
Interaction of formulation and crop
F1T1 1.44 1.60 1.97 1.06 0.97 0.70 0.53 0.36
F1T2 0.39 1.20 1.37 0.95 0.67 0.44 0.16 0.05
F2T1 1.59 1.16 0.81 0.59 0.45 0.29 0.17 0.09
F2T2 0.81 0.78 0.72 0.69 0.67 0.39 0.21 0.03
SE 0.013 0.008 0.012 0.018 0.006 0.008 0.004 0.003
CD (0.05) 0.037 0.023 0.032 0.049 0.015 0.022 0.011 0.008
64
with cropped condition. In this table on 7th day the combined effects F1T2 (Granule
formulation under cropped condition) and F2T2 (EC formulation under cropped
condition) were on par and on 15th day, the residues detected by the combined effects
of F1T2 (granule formulation under cropped condition) and F2T1 (EC formulation
under laboratory condition) were on par.
The combined effect of soil types and treatments on the dissipation of
carbosulfan are presented in Table 33 and it showed that, the combined effect of
laterite soil with 5 mg kg-1 level of carbosulfan had high retention (0.29 mg kg-1).
The combined effect of coastal alluvial soil with 1 mg kg-1 level of carbosulfan
resulted in residue level below the detectable level. On 0th day, the combined effect of
two soils with 2.5 mg kg-1 level of treatment was found to be on par. From 3rd day to
7th day and on 15th day, the combined effects of laterite soil with 2.5 mg kg-1 and
coastal alluvial soil with 5 mg kg-1 level showed as on par. On the 20th day, the
combined effect of laterite soil with 1 mg kg-1 and coastal alluvial soil combined
effect with 2.5 mg kg-1 were on par in terms of residue content.
The combined effect effect of formulations and treatment levels given in
Table 33 revealed that, a higher retentions of carbosulfan as granules with 5 mg kg-1
level treatment (0.34 mg kg-1). The combined effect of EC formulation with 1 mg
kg-1 level showed BDL residues on 20th day. On 20th day, the combined effects
F1P1 (granules formulation at 1 mg kg-1) and F2P2 (EC formulation at 2.5mg kg-1)
are on par and all others were significantly different. For EC formulation, the highest
residue content was seen with 5 mg kg-1 level on all days.
The combined effect of crop/ condition with treatment levels presented in
Table 34 revealed that on all the days of incubation, the 5 mg kg-1 level under
laboratory condition showed highest residue content (0.23 mg kg-1) than all other
combination. On 5th day, the combined effect of T1P1 (laboratory condition at 1 mg
kg-1) and T2P1 (cropped condition at 1 mg kg-1) were found to be on par. On 20th day
65
Table 33. Dissipation of carbosulfan as influenced by soil, formulations and treatment levels
S1- Laterite soil, S2- Coastal alluvial soil, F1- EC, F2- Granules, P1, P2, P3- 1, 2.5 and 5 mg kg-1 respectively.*BDL-Below
Detectable Level
Interactions*
Residues of carbosulfan ( mg kg-1)
Days after treatment
0 1 3 5 7 10 15 20
Interaction of soil and treatment levels
S1P1 0.36 0.46 0.46 0.43 0.32 0.17 0.08 0.02
S1P2 0.71 1.10 1.20 0.84 0.67 0.49 0.29 0.07
S1P3 1.53 2.30 2.44 2.09 1.80 1.32 0.89 0.29
S2P1 0.42 0.36 0.32 0.24 0.19 0.08 0.03 BDL
S2P2 0.69 0.63 0.59 0.53 0.39 0.23 0.16 0.02
S2P3 1.24 0.92 1.17 0.79 0.66 0.43 0.29 0.11
Interaction of formulation and treatment levels
F1P1 0.40 0.61 0.67 0.40 0.27 0.17 0.64 0.02
F1P2 0.74 1.30 1.54 0.81 0.61 0.44 0.28 0.08
F1P3 1.64 2.40 2.82 1.82 1.60 1.10 0.68 0.34
F2P1 0.86 0.49 0.36 0.24 0.11 0.09 0.46 BDL
F2P2 1.05 0.76 0.62 0.47 0.32 0.28 0.17 0.02
F2P3 1.57 1.13 0.99 0.76 0.69 0.66 0.51 0.07
SE 0.016 0.010 0.014 0.022 0.007 0.009 0.005 0.002
CD (0.05) 0.045 0.030 0.039 0.060 0.019 0.027 0.014 0.006
66
Table 34. Dissipation of carbosulfan as influenced by interaction of crop and treatment levels
T1- Laboratory condition, T2- Cropped Condition, P1- 1 mg kg-1, P2- 2.5 mg kg-1, P3- 5 mg kg-1 *BDL-BelowDetectableLevel
Treatments
Residues of carbosulfan (mg kg-1)
Days after treatments
0 1 3 5 7
10 15 20
T1P1 0.39 0.44 0.44 0.32 0.29 0.16 0.08 0.02
T1P2 0.78 0.91 0.74 0.64 0.57 0.42 0.26 0.07
T1P3 1.87 1.70 1.61 1.41 1.4 0.94 0.71 0.23
T2P1 0.37 0.36 0.33 0.29 0.20 0.09 0.03 BDL
T2P2 0.71 0.67 0.59 0.53 0.51 0.31 0.18 0.02
T2P3 1.31 1.25 1.08 0.97 0.92 0.83 0.48 0.10
SE 0.016 0.010 0.014 0.022 0.007 0.009 0.005 0.002
CD (0.05) 0.045 0.030 0.039 0.060 0.019 0.027 0.014 0.006
67
T1P1 and T2P2 (Cropped condition with 2.5 mg kg-1) were found to be on par. T2P1
shows BDL residues on the 20th day. The cropped condition combined effect with 5
mg kg-1 level (T2P3) shows lesser residue content than the laboratory situation
combined effect with 5 mg kg-1 level (T1P3) on all the days.
4.5 DEGRADATION OF CARBOSULFAN IN SOIL
Carbosulfan, primarily a pro-insecticide which when applied to the soil will
get metabolized and the major metabolites viz., carbofuran, 3-hydroxy carbofuran and
3-keto carbofuran will be formed. There exists an inverse relation between the
metabolites formed and concentration of carbosulfan. The formation of metabolite
increased with a consequent lowering of carbosulfan concentration with time. The
data on degradation of carbosulfan in the two soils applied as two formulations in two
situations are presented in the following tables.
4.5.1 Metabolism of Carbosulfan 25 EC in Laterite Soil under Laboratory
Condition
The data on the metabolism of carbosulfan in laterite soil by using EC
formulation under laboratory condition is presented in Table 35. The result revealed
that, the presence of carbofuran formed from carbosulfan was detected from 0th day
which increased upto 15th day and then declined at all levels (1, 2.5 and 5 mg kg-1).
The maximum carbofuran was formed on 15th day and then declined thereafter. On
0th day the residues obtained were 0.239, 0.610 and 0.746 mg kg-1 at 1, 2.5and 5 mg
kg-1 levels respectively, and that were obtained upto 45th day which were 0.357, 0.954
and 1.80 mg kg-1 respectively. Other metabolites formed from carbofuran during its
degradation were 3- hydroxy carbofuran and 3- keto carbofuran. Formation of 3-
hydroxy carbofuran was observed from 3rd day onwards and was maximum on 15th
day and then declined. In the case of 3-keto carbofuran, maximum residue was
obtained on 20th day after treatment.
68
Table 35. Metabolites of carbosulfan 25 EC in the laterite soils under laboratory condition
Mean of five replications, *BDL- Below Detectable Level (0.01 mg kg-1)
Compound Treatment
Level
Residues in mg kg-1
Days after treatment
0 1 3 5 7 10 15 20 30 45
Carbofuran 1 mg kg-1 0.239 0.303 0.475 0.496 0.724 0.777 1.951 1.34 0.877 0.357
2.5 mg kg-1 0.610 0.704 0.816 0.951 1.345 1.525 3.082 2.781 1.631 0.954
5 mg kg-1 0.746 0.856 1.050 1.240 1.520 1.861 4.660 4.021 3.170 1.800
3-Hydroxy
carbofuran 1 mg kg-1 BDL BDL BDL BDL 0.011 0.012 0.013 0.011 0.011 BDL
2.5 mg kg-1 BDL BDL 0.011 0.012 0.012 0.014 0.015 0.014 0.012 BDL
5 mg kg-1 BDL 0.011 0.011 0.013 0.014 0.012 0.291 0.132 0.078 0.011
3-Keto
carbofuran 1 mg kg-1 BDL BDL BDL BDL BDL BDL 0.011 0.013 0.014 0.011
2.5 mg kg-1 BDL BDL BDL BDL 0.015 0.017 0.016 0.111 0.017 0.013
5 mg kg-1 BDL BDL 0.014 0.017 0.026 0.038 0.121 0.156 0.036 0.008
69
4.5.2 The Metabolism of Carbosulfan 25 EC in Coastal Alluvial Soil under
Laboratory Condition
The data on the metabolism of carbosulfan in coastal alluvial soil by using EC
formulation under laboratory condition is presented in Table 36. The result revealed
that, the presence of carbofuran formed from carbosulfan was detected on 0 th day and
increased upto 10th day and then declined at all the three levels. The maximum
carbofuran was formed on 10th day and then declined thereafter. On 0th day, the
residues obtained were 0.284, 0.533 and 1.181 mg kg-1 at 1, 2.5 and 5 mg kg-1 levels
respectively, and that were obtained upto 45th day which were 0.111, 0.114 and 0.212
mg kg-1 respectively. Formation of 3- hydroxy carbofuran was observed from 3rd
day onwards for 1 mg kg-1 level and for 2.5 and 5 mg kg-1 level, it started from 0th
day itself and was maximum on 15th day and then declined. In the case of 3-keto
carbofuran, maximum residue was obtained on 15th day after treatment.
4.5.3 The Metabolism of Carbosulfan in Laterite Soil by Using Granule
Formulation under Laboratory Condition
The data on the metabolism of carbosulfan in laterite soil by using granule
formulation under laboratory condition is presented in Table 37. The result revealed
that, the presence of carbofuran formed from carbosulfan was detected on 0 th day and
increased upto 10th day and then declined at all levels of treatments. The maximum
carbofuran was formed on 10th day and then declined thereafter. On 0th day, the
residues obtained were 0.129, 0.321 and 0.515 mg kg-1 at 1, 2.5 and 5 mg kg-1 levels
respectively, and that were obtained upto 30th day which were 0.089, 0.109 and 0.522
mg kg-1 respectively. Formation of 3- hydroxy carbofuran was observed from 3rd day
onwards at 1 mg kg-1 level of treatment and for 2.5 and 5 mg kg-1 level it started from
0th day itself and was maximum on 15th day and then declined. In the case of 3-keto
carbofuran, maximum residue was obtained on 15th day after treatment.
70
Table 36. Metabolites of carbosulfan 25 EC in the coastal alluvial soil under laboratory condition
Mean of five replications, *BDL- Below Detectable Level (0.01 mg kg-1)
Compound Treatment
Level Residue in mg kg-1
Days after treatment
0 1 3 5 7 10 15 20 30 45
Carbofuran 1 mg kg-1 0.284 0.360 0.415 0.573 0.666 0.360 0.296 0.232 0.136 0.011
2.5 mg kg-1 0.533 0.628 0.735 0.837 0.931 0.751 0.516 0.446 0.279 0.114
5 mg kg-1 1.181 1.727 1.845 1.655 2.155 1.342 1.172 0.981 0.755 0.212
3-Hydr oxy carbofuran
1 mg kg-1 BDL BDL 0.011 0.011 0.013 0.014 0.015 0.014 0.011 BDL
2.5 mg kg-1 0.011 0.012 0.013 0.014 0.014 0.014 0.015 0.014 0.012 0.011
5 mg kg-1 0.013 0.015 0.016 0.015 0.016 0.013 0.014 0.015 0.012 0.012
3-Keto carbofuran
1 mg kg-1 BDL BDL 0.002 0.024 0.025 0.027 0.030 0.020 0.069 0.011
2.5 mg kg-1 BDL 0.015 0.015 0.057 0.065 0.0635 0.077 0.059 0.160 0.012
5 mg kg-1 0.011 0.011 0.051 0.121 0.237 0.391 0.414 0.281 0.106 0.058
71
Table 37. Metabolites of carbosulfan granules in laterite soil under laboratory condition
Mean of five replications, *BDL- Below Detectable Level (0.01 mg kg-1)
Compound Treatment
Level
Residue in mg kg-1
Days after treatment
0 1 3 5 7 10 15 20 30 45
Carbofuran 1 mg kg-1 0.129 0.193 0.223 0.272 0.314 0.331 0.212 0.129 0.089 BDL
2.5 mg kg-1 0.321 0.373 0.409 0.467 0.517 0.581 0.346 0.234 0.109 BDL
5 mg kg-1 0.515 0.676 0.725 0.810 0.973 1.0975 0.820 0.689 0.522 BDL
3-Hydroxy
carbofuran 1 mg kg-1 BDL BDL 0.011 0.011 0.012 0.016 0.012 0.011 0.011 BDL
2.5 mg kg-1 0.011 0.012 0.013 0.014 0.014 0.014 0.013 0.014 0.012 BDL
5 mg kg-1 0.013 0.015 0.016 0.016 0.016 0.018 0.013 0.011 0.014 BDL
3-Keto carbofuran
1 mg kg-1 BDL BDL 0.002 0.024 0.025 0.027 0.030 0.020 0.069 BDL
2.5 mg kg-1
BDL 0.015 0.015 0.057 0.065 0.064 0.077 0.059 0.106 BDL
5 mg kg-1
0.013 0.011 0.052 0.121 0.237 0.391 0.414 0.281 0.160 BDL
72
4.5.4 The Metabolism of Carbosulfan Granules in Coastal Alluvial Soil under
Laboratory Condition
The data on the metabolism of carbosulfan in coastal alluvial soil by using
granule formulation under laboratory condition is presented in Table 38. The result
revealed that the presence of carbofuran formed from carbosulfan was detected on 0th
day and increased upto 7th day and then declined at all levels of treatments. The
maximum carbofuran was formed on 7th day and then declined thereafter. On 0th
day, the residues obtained were 0.047, 0.297 and 0.787 mg kg-1 at 1, 2.5 and 5 mg
kg-1 levels respectively, and that were obtained upto 30th day which were 0.036, 0.148
and 0.314 mg kg-1 respectively. Formation of 3- hydroxy carbofuran was observed
from 5th day onwards at 1 mg kg-1 level of treatment and for 2.5 and 5 mg kg-1 level,
it started from 1st day itself and was maximum on 15th day and then declined. In the
case of 3-keto carbofuran, maximum residue was obtained on 7th day after treatment.
4.5.5 The Metabolism of Carbosulfan 25 EC in Laterite Soil under Cropped
Condition
The data on the metabolism of carbosulfan in laterite soil by using EC
formulation under cropped condition is presented in Table 39. The result revealed the
presence of carbofuran formed from carbosulfan on 0th day and increased upto 7th day
and then declined at all levels of treatments. The maximum carbofuran was formed
on 7th day and then declined thereafter. On 0th day, the residues obtained were 0.027,
0.083 and 0.126 mg kg-1 at 1, 2.5and 5 mg kg-1 levels respectively, and that were
obtained upto 30th day which were 0.023, 0.095 and 0.129 mg kg-1 respectively.
Formation of 3- hydroxy carbofuran was observed from 1st day onwards at 5 mg kg-1
level of treatment and for 1 and 2.5 mg kg-1 level it started from 7th and 3rd day,
respectively and was maximum on 7th day and then declined. In the case of 3-keto
carbofuran, maximum residue was obtained on 10th day after treatment.
73
Table 38. Metabolites of carbosulfan granules in the coastal alluvial soil under laboratory condition.
Mean of five replications, *BDL- Below Detectable Level (0.01 mg kg-1)
Compound Treatment
Level
Residue in mg kg-1
Days after treatment
0 1 3 5 7 10 15 20 30 45
Carbofuran 1 mg kg-1 0.047 0.293 0.336 0.400 0.526 0.309 0.219 0.204 0.036 BDL
2.5 mg kg-1 0.297 0.415 0.447 0.533 0.564 0.419 0.314 0.299 0.148 BDL
5 mg kg-1 0.787 0.885 0.936 0.982 1.131 1.010 0.807 0.629 0.314 BDL
3-Hydroxy carbofuran
1 mg kg-1 BDL BDL BDL 0.011 0.011 0.012 0.012 0.011 0.011 BDL
2.5 mg kg-1 BDL 0.011 0.013 0.012 0.014 0.016 0.045 0.015 0.012 BDL
5 mg kg-1 BDL 0.013 0.014 0.015 0.016 0.011 0.018 0.015 0.012 BDL
3-Keto carbofuran
1 mg kg-1 BDL BDL BDL 0.011 0.014 0.012 0.012 0.011 BDL BDL
2.5 mg kg-1
BDL BDL 0.014 0.012 0.015 0.014 0.013 0.013 0.012 BDL
5 mg kg-1
0.011 0.012 0.013 0.016 0.019 0.015 0.014 0.013 BDL BDL
74
Table 39. Metabolites formed in the laterite soil by application of carbosulfan 25 EC in the cropped condition
Mean of five replications, *BDL- Below Detectable Level (0.01 mg kg-1)
Compound Treatment
Level Residue in mg kg-1 Days after treatment
0 1 3 5 7 10 15 20 30 45
Carbofuran 1 mg kg-1 0.027 0.038 0.093 0.321 0.389 0.283 0.232 0.124 0.023 BDL
2.5 mg kg-1 0.083 0.113 0.189 0.435 0.529 0.395 0.259 0.195 0.095 BDL
5 mg kg-1 0.126 0.226 0.322 0.591 0.763 0.553 0.309 0.225 0.129 BDL
3-Hydroxy carbofuran
1 mg kg-1 BDL BDL BDL BDL 0.013 0.011 BDL BDL BDL BDL
2.5 mg kg-1 BDL BDL 0.011 0.013 0.014 0.012 0.011 BDL BDL BDL
5 mg kg-1 0.011 0.013 0.020 0.020 0.012 0.020 0.018 BDL BDL BDL
3-Keto
carbofuran 1 mg kg-1
BDL BDL BDL 0.012 0.014 0.016 0.012 BDL BDL BDL
2.5 mg kg-1
BDL 0.011 0.011 0.016 0.019 0.020 0.011 BDL BDL BDL
5 mg kg-1
0.011 0.020 0.020 0.031 0.045 0.065 0.016 BDL BDL BDL
75
4.5.6 The Metabolism of Carbosulfan 25 EC in Coastal Alluvial Soil under
Cropped Condition
The data on the metabolism of carbosulfan in coastal alluvial soil by using EC
formulation under cropped condition is presented in Table 40. The results revealed
the presence of carbofuran formed from carbosulfan as detected on 0th day and
increased upto 10th day and then declined at all levels of treatment. The maximum
carbofuran was formed on 10th day and then declined thereafter. On 0th day, the
residues obtained were 0.254, 0.346 and 0.434 mg kg-1 at 1, 2.5 and 5 mg kg-1 levels
respectively, and that were obtained upto 20th day which were 0.235, 0.317 and 0.044
mg kg-1 respectively. Formation of 3- hydroxy carbofuran was observed from 1st day
onwards at 5 mg kg-1 level of treatment and for 1 and 2.5 mg kg-1 level, it started
from 7th and 5th day, respectively and was maximum on 10th day and then declined.
In the case of 3-keto carbofuran, maximum residue was obtained on 10th day after
treatment.
4.5.7 The Metabolism of Carbosulfan Granule in Laterite Soil under Cropped
Condition
The data on the metabolism of carbosulfan in laterite soil by using granule
formulation under cropped condition is presented in Table 41. The result revealed
that, carbofuran formed from carbosulfan was detected on 0th day and increased upto
10th day and then declined at all levels of treatments. The maximum carbofuran was
formed on 10th day and then declined thereafter. On 0th day, the residues obtained
were 0.035, 0.095and 0.255 mg kg-1 at 1, 2.5 and 5 mg kg-1 levels respectively, and
that were obtained upto 45th day which were 0.021, 0.234 and 0.417 mg kg-1
respectively. Formation of 3- hydroxy carbofuran was observed from 1st day onwards
at 5 mg kg-1 level of treatment and for 1 and 2.5 mg kg-1 level it started from 10th and
5th day, respectively and was maximum on 10th day and then declined. In the case of
3-keto carbofuran maximum residue was obtained on 15th day after treatment.
76
Table 40. Metabolites formed in the coastal alluvial soil by application of carbosulfan 25 EC in the cropped condition
Mean of five replications, *BDL- Below Detectable Level (0.01 mg kg-1)
Compound Treatment
Level Residue in mg kg-1 Days after treatment
0 1 3 5 7 10 15 20 30 45
Carbofuran 1 mg kg-1 0.254 0.309 0.379 0.453 0.511 0.549 0.368 0.235 BDL BDL
2.5 mg kg-1 0.346 0.402 0.493 0.549 0.613 0.688 0.486 0.317 BDL BDL
5 mg kg-1 0.434 0.483 0.574 0.634 0.702 0.874 0.613 0.444 BDL BDL
3-Hydroxy
carbofuran 1 mg kg-1 BDL BDL BDL BDL 0.012 0.021 0.014 BDL BDL BDL
2.5 mg kg-1 BDL BDL BDL 0.010 0.015 0.023 0.012 BDL BDL BDL
5 mg kg-1 BDL 0.011 0.015 0.018 0.024 0.031 0.015 BDL BDL BDL
3-Keto carbofuran
1 mg kg-1 BDL BDL BDL BDL 0.013 0.028 0.012 BDL BDL BDL
2.5 mg kg-1
BDL BDL BDL 0.013 0.025 0.037 0.013 BDL BDL BDL
5 mg kg-1
BDL 0.014 0.018 0.027 0.045 0.065 0.026 0.014 BDL BDL
77
Table 41. Metabolites formed in the laterite soil by application of carbosulfan granules in the cropped condition
Mean of five replications, *BDL- Below Detectable Level (0.01 mg kg-1)
Compound Treatment
Level Residue in mg kg-1 Days after treatment
0 1 3 5 7 10 15 20 30 45
Carbofuran 1 mg kg-1 0.035 0.056 0.120 0.279 0.311 0.477 0.209 0.021 BDL BDL
2.5 mg kg-1 0.095 0.128 0.310 0.503 0.686 0.845 0.515 0.234 BDL BDL
5 mg kg-1 0.255 0.335 0.482 0.806 0.984 1.250 0.741 0.417 BDL BDL
3-Hydroxy carbofuran
1 mg kg-1 BDL BDL BDL BDL BDL 0.012 0.011 BDL BDL BDL
2.5 mg kg-1 BDL BDL BDL 0.014 0.018 0.013 0.011 BDL BDL BDL
5 mg kg-1 BDL 0.011 0.011 0.012 0.012 0.011 0.011 BDL BDL BDL
3-Keto carbofuran
1 mg kg-1 BDL BDL BDL BDL 0.011 0.012 0.012 0.010 BDL BDL
2.5 mg kg-1 BDL BDL 0.012 0.012 0.014 0.014 0.021 0.016 BDL BDL
5 mg kg-1 0.011 0.012 0.012 0.014 0.015 0.057 0.109 0.068 BDL BDL
78
4.5.8 The Metabolism of Carbosulfan Granules in Coastal Alluvial Soil under
Cropped Condition
The data on the metabolism of carbosulfan in coastal alluvial soil by using
granule formulation under cropped condition is presented in Table. 42. The result
revealed that, carbofuran formed from carbosulfan was detected on 0th day and
increased upto 7th day and then declined at all levels of treatments. The maximum
carbofuran was formed on 7th day and then declined thereafter. On 0th day, the
residues obtained were 0.239, 0.610 and 0.746 mg kg-1 at 1, 2.5and 5 mg kg-1 levels
respectively, and that were obtained upto 45th day which were 0.088, 0.079 and 0.238
mg kg-1 respectively. Formation of 3- hydroxy carbofuran was observed from 0th day
onwards at 5 mg kg-1 level of treatment and for 1 and 2.5 mg kg-1 level, it started
from 5th and 3rd day, respectively and was maximum on 10th day and then declined.
In the case of 3-keto carbofuran, maximum residue was obtained on 10th day after
treatment.
4.6 EFFECT OF CARBOSULFAN ON SOIL ORGANISMS
The effect of carbosulfan on soil microbes in laterite and coastal alluvial soils
were studied after addition of carbosulfan EC and granules at normal (250 g ai ha-1)
and at double doses (500g ai ha-1) to the two soils under field condition. The results
of enumeration of various microbes viz., bacteria, fungi, actinomycete and arthropods
are presented in the following tables.
4.6.1 Effect of Carbosulfan on Microbial Population in Laterite Soil
The effect of carbosulfan on bacterial load when applied in laterite soil is
presented in Table. 43. The data revealed that, the bacterial population was found to
be increased by treating with EC formulation in normal (250 g ai ha-1) and double
(500 g ai ha-1) doses. The application of EC formulation at normal dose has a
bacterial population of 9.45 x 106 cfu g-1 (37.75 % increase) and at double dose, the
79
Table 42. Metabolites formed in the coastal alluvial soil by the application of carbosulfan granules under cropped condition
Mean of five replications, *BDL- Below Detectable Level (0.01 mg kg-1)
Compound Treatment
Level Residue in mg kg-1 Days after treatment
0 1 3 5 7 10 15 20 30 45
Carbofuran 1 mg kg-1 0.034 0.176 0.242 0.299 0.306 0.223 0.088 BDL BDL BDL
2.5 mg kg-1 0.289 0.432 0.538 0.626 0.734 0.544 0.281 0.079 BDL BDL
5 mg kg-1 0.796 0.817 0.843 0.930 1.09 0.834 0.529 0.238 BDL BDL
3-Hydroxy
carbofuran 1 mg kg-1 BDL BDL BDL 0.013 0.022 0.027 0.011 BDL BDL BDL
2.5 mg kg-1 BDL BDL 0.014 0.018 0.024 0.032 0.021 0.031 BDL BDL
5 mg kg-1 0.011 0.014 0.019 0.026 0.035 0.043 0.022 0.011 BDL BDL
3-Keto carbofuran
1 mg kg-1 BDL BDL 0.012 0.015 0.018 0.024 0.013 0.012 BDL BDL
2.5 mg kg-1 BDL 0.013 0.023 0.027 0.035 0.041 0.022 0.017 BDL BDL
5 mg kg-1 0.017 0.019 0.025 0.028 0.041 0.079 0.039 0.019 BDL BDL
80
Table 43. Effect of carbosulfan treatments on the population of soil organisms in laterite soil
Treatments
Bacterial
Population
(106cfu g-1 soil)
Fungal
Population (104
cfu g-1soil)
Actinomycetes
Population
(104cfu g-1soil)
Arthropod
Population (per kg
soil)
Carbosulfan 25 EC at 250g ai ha-1
9.451 (+ 37.75)
4.485 (- 22.27)
4.225 (- 14.56)
10.750 (- 18.87)
Carbosulfan 25 EC at 500 g ai ha-1
7.200 (+ 4.96)
5.330 (- 11.01)
3.355 (-32.15)
5.750 (-56.60)
Carbosulfan G at 250g ai ha-1
4.790 ( _ 30.17)
3.595 (- 40.06)
6.585 (+ 33.16)
6.750 (- 49.06)
Carbosulfan G at 500g ai ha-1
5.550 ( -19.09)
6.100 ( + 1.92)
3.820 (- 22.75)
7.750 (- 41.51)
Control 6.860 5.985 4.945 13.250
CD (0.05) 1.268 0.581 1.21 2.39
Mean of four replications, *cfu- colony forming units
Values in the paranthesis indicate per cent enhancement (+) or per cent inhibition (-) in the population over control.
81
bacterial population was 7.2x106 cfu g-1 (4.96 %) over the control population
(6.86x106 cfu g-1). The data revealed 32.79 per cent inhibition in the bacterial
population at double dose of application of EC compared to normal dose. The
granules treated soils in normal and double doses had population 4.75 and 5.55 x106
cfu g-1 respectively. The highest inhibition (30.17 %) in the bacterial population was
found by using carbosulfan granules in normal dose.
In the case of fungal population, except for granules at double doses all other
treatment inhibited fungal population over the control soil. Statistically, the fungal
population with granule application at double dose was on par with that in the control
soil. All other treatments were significantly different with EC treatment in the normal
dose which inturn resulted in 22.27 per cent reduction over control, while at double
doses, the corresponding inhibition was only 11.01 per cent. The granular treatment
in the normal dose resulted in 4.06 per cent reduction while at double doses, a 1.92
per cent increase in the count of fungi was observed over control.
The soil treated with granules at normal dose showed highest (6.585x 104 cfu
g-1) actinomycetes count which was 33.16 per cent more than the control. All other
treatments inhibited the activity of actinomycetes than the control soil. Application of
EC form at double dose resulted in maximum inhibition (32.15 %), than granule at
double dose (22.75 %), which indicated a high potential for inhibition by EC at
higher concentrations.
The effect of carbosulfan application on the arthropod count revealed a
significant inhibition from all the treatments, with maximum inhibition with EC at
double dose. Granular formulations significantly suppressed the population of
arthropods to the tune of upto 49 per cent. The initial population of 13.25 kg-1 soil got
declined to 10.75 and 5.75 by EC application while it got declined to 6.75 and 7.75
kg-1 soil with granular application, indicating significant negative effect on arthropod
population.
82
4.6.2 Effect of Carbosulfan on the Microbial Population of Coastal Alluvial Soil
The data regarding the effect of carbosulfan on microbial population in
coastal alluvial soil was presented in Table. 44. The soil treated with carbosulfan EC
in normal and double the doses had a bacterial population of 19.5 and 12.27 x 106 cfu
g-1 soil indicating 66.38 and 4.56 per cent increase respectively, over the control
(11.735x106 cfu g-1) soil. The soil treated with carbosulfan granules in normal dose
showed the highest bacterial population of 20.36 x106 cfu g-1 (73.44 % increase)
among all the treatments. In the double dose granule application it was 10.2 x 106 cfu
g-1 soil indicating a further reduction of 60.36 per cent over the normal granule
application. The statistical analysis showed that, the normal dose application of EC
and granules are on par and all other treatments including double dose of EC and
granules were on par with the control soil as regards to bacterial population.
In control soil, the fungal population was 7.66x104 cfu g-1 soil, while when
treated with EC at normal dose, the population increased to 9.715 x104 cfu g-1 and
got declined to 5.215 x104 cfu g-1, at double doses of EC indicating considerable
inhibition (58 %) at higher dose over the normal dose. In the case of granule
treatment, the fungal population was inhibited at both the levels to 6.6 at normal dose
and 4.8 x104 cfu g-1 in double dose, from 7.7 x104 cfu g-1 in control. The double dose
application of granule resulted in an inhibition of upto 36.86 per cent of fungal
population. Statistical analysis of the treatments revealed that, the double dose
application of the EC and granules were on par and all other treatments were found to
be significantly different.
The effect of carbosulfan on the actinomycetes population revealed that, both
the normal dose of EC and granules had a positive effect on the actinomycetes
population, but at double doses, both the formulations had a negative effect. The
control soil had a population of 3.89 x104 cfu g-1, which got enhanced to 4.45 and 4.6
x104 cfu g-1 indicated 14.63 and 18.51 per cent increase respectively, for normal
83
Table 44. Effect of carbosulfan treatments on the population of soil organisms in
coastal alluvial soil
Treatments
Bacterial
Population
(106cfu g-
1soil)
Fungal
Population (104
cfu g-1 soil)
Actinomycetes
Population
(104cfu g-1soil)
Arthropod
Population (per
kg soil)
Carbosulfan 25EC at 250 g ai ha-1
19.525
(+ 66.38)
9.715
(+ 26.74)
4.459
(+ 14.63)
12.500
(- 28.57)
Carbosulfan 25EC at 500 g ai ha-1
12.270
(+ 4.56)
5.215
(– 31.96)
2.215
(- 43.06)
9.750
(- 44.29)
Carbosulfan G at 250 g ai ha-1
20.354
(+ 73.44)
6.565
(- 14.35)
4.610
(+ 18.51)
10.500
(- 40.00)
Carbosulfan G at 500 g ai ha-1
10.200
(- 13.08)
4.840
(- 36.86)
3.227
(- 17.04)
8.750
(- 50.00)
Control 11.735 7.665 3.890 17.500
CD (0.05) 2.400 0.878 0.368 1.485
Mean of four replications, *BDL- Below Detectable Level, cfu- colony forming unit
Values in the paranthesis indicate per cent enhancement (+) or per cent inhibition (-)
in the population over control.
84
doses of EC and granule and were found on par with each other. When the dose was
doubled the population declined to 2.21 and 3.23x104 cfu g-1 soil indicating 43.06 and
17.04 per cent reduction, respectively in EC and granules, which differ significantly.
The effect of carbosulfan application on the arthropod count was checked and
all the treatments in general decreased the arthropod count. In control soil, the total
count was 17.5 kg-1 which got decreased to 10.75 kg-1 soil corresponding to a 28.57
per cent inhibition by EC application at normal dose. The effect of normal dose of
EC and double dose of granule were on par. With increased concentration of the EC
the arthropod count declined upto 44.29 per cent over control. The granule
application at normal dose decreased the population by 40 per cent while that for
double dose was 50 per cent.
85
Discussion
5. DISCUSSION
Carbosulfan is one among the few carbamate insecticides now available for
pest control purposes and is preferred over other insecticides owing to its more safety,
less toxicity, availability in solid and liquid forms and wide application spectrum.
Though carbosulfan is relatively safe, it is reported to get metabolized resulting in the
formation of carbofuran and other derivatives such as 3- hydroxy and 3-keto
carbofuran. So, this metabolism is likely to pose certain risks in the use of
carbosulfan in soil. In this context, a study was conducted on the persistence and
transformation of carbosulfan in laterite and coastal alluvial soils of Kerala and its
effect on soil organisms. The results obtained from the study are discussed under the
following heads.
5.1 PHYSICO - CHEMICAL PROPERTIES OF SOIL
The physico - chemical properties of the two soils were estimated as per
standard procedures and the results are presented in Tables. 6 and 7. The two soils
used for the study were strongly acidic with a pH 5.08 for laterite soil and 5.18 for
coastal alluvial soil. The porosity, bulk density, particle density, WHC and field
moisture percentage were more in laterite soil than coastal alluvial soil. The EC and
CEC were more in coastal alluvial soil compared to laterite soil. Primary and
secondary nutrients were also high in coastal alluvial soil due to high organic matter
(0.84 %) content, high CEC (7.11 cmol kg-1) and low 1:1 clay minerals. In laterite
soil, the low CEC and OM and the high content of 1:1 clay minerals resulted in a
decreased reserve of primary and secondary nutrients. The laterite soil comes under
the sandy loam soil type with > 60 per cent total sand content, 27 per cent silt content
while the coastal alluvial soil comes under the loamy sand soil type with > 80 per
cent total sand and 8.48 per cent silt content. So, the hydraulic conductivity of
coastal alluvial soil is more (0.6 mL min-1) than laterite soil (0.4 mL min-1). The
more silt and clay content in laterite soil resulted in the relatively high WHC and field
86
moisture percentage in laterite soil than coastal alluvial soil. Laterite soil comes
under the taxonomic class of Typic Kandiustult of Vellayani Series while coastal
alluvial belongs to the taxonomic class of Ustic Quartzipsamment.
5.2 STANDARDIZATION OF ANALYTICAL PROCEDURE FOR
MULTIRESIDUE METHOD VALIDATION
The result of recovery experiment for standardizing the analytical procedure
for estimation of carbosulfan and its metabolites (Table 8-13) in the two soils
revealed that, extraction of the residues using acetonitrile followed by MgSO4 and
Primary Secondary Amine (PSA) sorbent clean up and centrifugation to collect
supernatant was found to be satisfactory and suitable at 0.05, 0.25 and 0.50 mg kg-1
levels. The recovery percentage ranged from 80- 99.20 per cent and 88.40 - 100.60
per cent in laterite soil and coastal alluvial soil respectively and relative standard
deviation ranged from 6.90 - 11.60 and 4.50- 8.40 for laterite and coastal alluvial soil
respectively. Since the values of recovery percentage and Relative Standard
Deviation (RSD) fall in the acceptable range of 70-110 per cent and < 20,
respectively and considering the less time, less solvent requirement and the
economics of the operation, the method was adopted for further analysis of
carbosulfan and its metabolite in soil.
5.3 MOBILITY OF CARBOSULFAN IN SOIL UNDER DIFFERENT
TREATMENTS
The mobility of carbosulfan as well as carbofuran in soil columns eluted with
water under different levels of carbosulfan were monitored in the laterite and in the
coastal alluvial soil using carbosulfan 25 EC at 100, 150 and 200 µg level of
carbosulfan loaded on the top and subsequent elution with 20, 40, 80 and 160 mL of
water, as per standard procedure which was considered equivalent to 50, 100, 200 and
400 mm of rainfall in the field condition.
87
5.3.1 Mobility of Carbosulfan in Laterite Soil
The data on the mobility of carbosulfan in soil column containing laterite and
coastal alluvial soil loaded at 100, 150 and 200 µg each of carbosulfan and eluted
with different volumes of water viz., 20, 40, 80 and 160 mL are given in Tables 15-
16 and the depth wise proliferation of residues depicted in Fig. 2-4.
The mobility of carbosulfan when loaded with 100 µg carbosulfan in laterite
soil was depicted on the Fig. 2. When leached with 20 mL water, the residues were
detected upto 10 cm only and 95 per cent of the residues were confined to the surface
layers alone. When the volume of water increased upto 160 mL, the residues moved
further down and were detected upto 15 cm and most of the residues were detected in
the 0-5 cm layer. It can be inferred from the above observations that carbosulfan
possess a high water solubility, (0.3 mg kg-1) due to which it moved down with
percolating water and at the same time possess a high adsorption to soil (Adsorption
Coefficient of 8500 mL g-1) which adsorbed the molecule on the upper layer and
when thoroughly eluted, it moved further, till a balance between the two is achieved.
Thus, the application of 20 mL water (T1) equivalent to 50 mm rainfall confined the
carbosulfan residues at the top layers while the application of 80 and 160 mL
equivalent to 200 and 400 mm rainfall respectively resulted the residues to leach
down to more deeper layers.
At 150 µg level of carbosulfan, downward mobility when eluted with
different volumes of water is depicted in Fig. 3. The data revealed that, at 20 mL
water addition, the residues were detected upto 10 cm and the concentration of
carbosulfan markedly increased in each layer than 100 µg level of application. With
increasing volume of water used for leaching purpose, the residues further moved
down and were detected upto 20 cm depth but in very low concentration.
At 200 µg level of carbosulfan, downward mobility when eluted with different
volume of water is depicted in Fig. 4. The data revealed that, at 20 mL
88
Fig. 2. Mobility of carbosulfan 25 EC at 100 µg in laterite soil
Fig. 3. Mobility of carbosulfan 25 EC at 150 µg in laterite soil
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0-5cm 5-10cm 10-15cm 15-20cm 20-25cm Leachate
Re
sid
ue
s in
mg
kg-1
DepthT1 T2 T3 T4
T1-100 µg carbosulfan EC + 20 mL water T2-100 µg carbosulfan EC + 40 mL waterT3-100 µg carbosulfan EC + 80 mL water T4-100 µg carbosulfan EC + 160 mL water
0
0.5
1
1.5
2
2.5
0-5cm 5-10cm 10-15cm 15-20cm 20-25cm Leachate
Re
sid
ue
s in
m
g kg
-1
DepthT1 T2 T3 T4
T1-150 µg carbosulfan EC + 20 mL water T2-150 µg carbosulfan EC + 40 mL waterT3-150 µg carbosulfan EC + 80 mL water T4-150 µg carbosulfan EC + 160 mL water
Fig. 4. Mobility of carbosulfan 25 EC at 200 µg in laterite soil.
Fig. 5. Mobility of carbosulfan 25 EC at 100 µg in coastal alluvial soil
0
0.5
1
1.5
2
2.5
3
3.5
4
0-5cm 5-10cm 10-15cm 15-20cm 20-25cm Leachate
Re
sid
ue
s in
m
g kg
-1
Depth T1 T2 T3 T4
T1-200 µg carbosulfan EC + 20 mL water T2-200 µg carbosulfan EC + 40 mL waterT3-200 µg carbosulfan EC + 80 mL water T4-200 µg carbosulfan EC + 160 mL water
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0-5cm 5-10cm 10-15cm 15-20cm 20-25cm Leachate
Re
sid
ue
s in
m
g kg
-1
Depth T1 T2 T3 T4
T1-100 µg carbosulfan EC + 20 mL water T2-100 µg carbosulfan EC + 40 mL waterT3-100 µg carbosulfan EC + 80 mL water T4-100 µg carbosulfan EC + 160 mL water
water addition the residues were detected upto 10 cm and a further increase in the concentration
was noticed than 150 µg level application. With increase in the volume of water used for
leaching upto 160 mL for the leaching purpose, the residues further moved down upto 25 cm and
the leachate also showed the presence of carbosulfan residues, even though its concentration was
very low.
This result is in accordance with the findings of Sreekumar and Shah (2014) in which
the residues of atrazine, imidacloprid and certain fertilizers moved to the deep layers from 12
cm to 30 cm by initial application of 100 mL 0.01 M CaCl2 and further addition of 50 mL 0.01 M
CaCl2. According to Ngan et al. (2005), the solubility of pesticide has a major role in its
movement in the soil column and hence with more volume of water added to the soil the
solubility of carbosulfan get increased and thus it moved to deeper layers. This is contrary to the
results of Shabeer and Gupta (2011) in which the movement of capropamid in soil when applied
at 50 µg level was detected with 95 per cent residues in the top 0-5 cm layer and no residues in
the leachate.
5.3.2 Mobility of Carbosulfan in Coastal Alluvial Soil
The data on the mobility of carbosulfan in soil column containing coastal alluvial soil
loaded at 100, 150 and 200 µg and eluted with different volumes of water viz., 20, 40, 80 and
160 mL water are given in the Tables 16-18 and the depth wise proliferation of residues are
depicted in Fig. 5-7.
The mobility of carbosulfan when loaded with 100 µg carbosulfan in coastal alluvial
soil is depicted in Fig. 5. When leached with 20 mL water, the residues were detected upto 15
cm which was higher than that of laterite soil under the same condition where the residues
moved upto 10 cm only. When the volume of water was increased upto 160 mL, the residues
moved further down and were detected upto 20 cm and most of the residues were detected in 0-5
cm layer. This may be due to the effect of solubility of the compound on the movement of
carbosulfan. The migration
89
Fig. 6 Mobility of carbosulfan 25 EC at 150 µg in coastal alluvial soil
Fig. 7. Mobility of carbosulfan 25 EC at 200 µg in coastal alluvial soil
0
0.5
1
1.5
2
2.5
0-5cm 5-10cm 10-15cm 15-20cm 20-25cm Leachate
Re
sid
ue
s in
m
g kg
-1
DepthT1 T2 T3 T4
T1-150 µg carbosulfan EC + 20 mL water T2-150 µg carbosulfan EC + 40 mL waterT3-150 µg carbosulfan EC + 80 mL water T4-150 µg carbosulfan EC + 160 mL water
0
0.5
1
1.5
2
2.5
3
3.5
4
0-5cm 5-10cm 10-15cm 15-20cm 20-25cm Leachate
Re
sid
ue
s in
m
g kg
-1
DepthT1 T2 T3 T4
T1-200 µg carbosulfan EC + 20 mL water T2-200 µg carbosulfan EC + 40 mL waterT3-200 µg carbosulfan EC + 80 mL water T4-200 µg carbosulfan EC + 160 mL water
of carbosulfan was found to be more in coastal alluvial soil than laterite soil which
can be presumably due to the predominance of macropores in the coastal alluvial soil
than the laterite soil.
At 150 µg level of carbosulfan, downward mobility when eluted with
different volume of water is depicted in Fig. 6. The data revealed that, at 20 mL
water addition, the residues were detected upto 15 cm and the concentration of
carbosulfan markedly increased in each layer than 100 µg level of application. With
increase in the volume of water used for leaching purpose, the residues moved further
down and were detected upto 20 cm and 25 cm depth at 80 mL and 160 mL water
respectively but in very low concentrations.
At 200 µg level of carbosulfan, downward mobility when eluted with
different volumes of water is depicted in Fig. 7. The data revealed that, with 20 mL
water addition, the residues could be detected upto 15 cm and a further increase in the
concentration was noticed than 150 µg level application in each layer. With increase
in the volume of water used for leaching upto 160 mL, the residues further moved
down upto 25 cm and the leachate also showed the presence of carbosulfan residues,
even though its concentration was very low but higher than that in the laterite soil.
The study on mobility revealed that, the movement of carbosulfan was more
in the coastal alluvial soil, because at 100 µg level, the movement was upto 10-15 cm
in laterite while that was upto 15-20 cm level in coastal alluvial soil. At 150 µg
level, the residues moved upto 15-20 cm layer in laterite soil while in the coastal
alluvial soil it was 20-25 cm. At 200 µg level, the residues found in the leachate was
comparatively higher than the laterite. So, it shows that, there may be a chance of
ground water pollution in coastal alluvial soil when the higher dose application of
carbosulfan intercept with high rainfall condition. This result is similar to the findings
of Osman and Cemile (2010) increased rainfall can result in ground water pollution
by leaching down of the pesticides. This result was also similar to the reports of
Kumar and Philip (2006) that endosulfan mobility was found to be more in sandy soil
90
than clayey soil. This result opposes the findings of Singh et al. (2013) regarding the
mobility of lindane in soil with high organic matter where high organic matter
content restricted the movement of pesticide to the deep layers and confined only to
the surface layers (0-6 cm).
5.3.3 Mobility of Carbofuran in Laterite Soil
The mobility of carbofuran in the soils were tracked along with carbosulfan
where carbofuran was not directly used or loaded in the soil column. Carbofuran was
detected from time of start of elution which could be formed as metabolite of
carbosulfan formed directly from it. The mobility of carbofuran was also tracked in
soil columns which is discussed hereunder.
The mobility of carbofuran in laterite soil is depicted in Fig. 8-10. The result
showed that, mobility of carbofuran at 100 µg level (Fig. 8.) of carbosulfan
application along with 20 mL water equivalent to 50 mm rainfall confined the
carbofuran residues upto 5 cm only, while application of 160 mL water equivalent to
400 mm rainfall migrated the residues upto 15 cm in the soil column.
At 150 µg level (Fig. 9), the presence of residues was found upto 15 cm at
160 mL water application while at 20 mL water the residues moved only upto 10 cm.
The concentration of residues in these layers were increased than the 100 µg level of
application. At 200 µg level application of carbosulfan, the residues found upto 20
cm layer by 160 mL water (Fig. 10) and for 20 mL water it was confined to 10 cm
only. But there was no carbofuran residues in the leachate .
5.3.4 Mobility of Carbofuran in Coastal Alluvial Soil
The mobility of carbofuran in coastal alluvial soil is depicted in Figures. 11-
13. In coastal alluvial soil at 100 µg level (Fig. 11.) the residues were found upto 15
cm layer for 160 mL, while for 20 mL water, the residues could be obtained upto 10
cm. At 150 µg level (fig 12) also, the residues were found upto 20 cm by application
of 160 mL water and the presence of residues from other treatments were found less
91
Fig. 8. Mobility of carbofuran formed from carbosulfan 25 EC at 100 µg in laterite
soil
Fig. 9. Mobility of carbofuran formed from carbosulfan 25 EC at 150 µg in laterite
soil
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0-5cm 5-10cm 10-15cm 15-20cm 20-25cm Leachate
Re
sid
ue
s in
p m
g kg
-1
Depth T1 T2 T3 T4
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0-5cm 5-10cm 10-15cm 15-20cm 20-25cm Leachate
Re
sid
ue
s in
m
g kg
-1
Depth T1 T2 T3 T4
T1-150 µg carbosulfan EC + 20 mL water T2-150 µg carbosulfan EC + 40 mL water T3-150 µg carbosulfan EC + 80 mL water T4-150 µg carbosulfan EC + 160 mL water
T1-100 µg carbosulfan EC + 20 mL water T2-100 µg carbosulfan EC + 40 mL water T3-100 µg carbosulfan EC + 80 mL water T4-100 µg carbosulfan EC + 160 mL water
Fig. 10. Mobility of carbofuran formed from carbosulfan 25 EC at 200 µg in laterite soil
Fig. 11. Mobility of carbofuran formed from carbosulfan 25 EC at 100 µg in coastal
alluvial soil
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0-5cm 5-10cm 10-15cm 15-20cm 20-25cm Leachate
Re
sid
ue
s in
m
g kg
-1
DepthT1 T2 T3 T4
T1-200 µg carbosulfan EC + 20 mL water T2-200 µg carbosulfan EC + 40 mL water T3-200 µg carbosulfan EC + 80 mL water T4-200 µg carbosulfan EC + 160 mL water
0
0.05
0.1
0.15
0.2
0.25
0-5cm 5-10cm 10-15cm 15-20cm 20-25cm Leachate
Re
sid
ue
s in
m
g kg
-1
DepthT1 T2 T3 T4
T1-100 µg carbosulfan EC + 20 mL water T2-100 µg carbosulfan EC + 40 mL water T3-100 µg carbosulfan EC + 80 mL water T4-100 µg carbosulfan EC + 160 mL water
Fig. 12. Mobility of carbofuran formed from carbosulfan 25 EC at 150 µg in coastal alluvial soil
Fig. 13. Mobility of carbofuran formed from carbosulfan 25 EC at 200 µg in coastal
alluvial soil
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0-5cm 5-10cm 10-15cm 15-20cm 20-25cm Leachate
Re
sid
ue
s in
m
g kg
-1
Depth T1 T2 T3 T4
T1-150 µg carbosulfan EC + 20 mL water T2-150 µg carbosulfan EC + 40 mL water T3-150 µg carbosulfan EC + 80 mL water T4-150 µg carbosulfan EC + 160 mL water
0
0.1
0.2
0.3
0.4
0.5
0.6
0-5cm 5-10cm 10-15cm 15-20cm 20-25cm Leachate
Re
sid
ue
s in
m
g kg
-1
Depth T1 T2 T3 T4
T1-200 µg carbosulfan EC + 20 mL water T2-200 µg carbosulfan EC + 40 mL water T3-200 µg carbosulfan EC + 80 mL water T4-200 µg carbosulfan EC + 160 mL water
in the deep layers. At 200 µg level (Fig. 13.), the residues were found upto 20 cm
and with increasing concentration of application of carbosulfan, the residue level in
each layer was also increased. In coastal alluvial soil also, the leachate did not show
the presence of carbofuran.
The migration of carbofuran was comparatively slow than that of carbosulfan
in two soils that may be the reason why the leachate showed no residues of
carbofuran. In coastal alluvial soil, the movement of carbofuran was slightly higher
than that in laterite soil. This is similar to the study by Lalah and Wandiga (1996)
where the movement of carbofuran was slightly higher in sandy soils than other soils.
The results of mobility of carbosulfan and carbofuran can be summarized as
follows. With increased concentration and increased volume of water for elution, the
movement of carbosulfan and carbofuran were increased. This indicates that, increase
in rainfall from 50 to 400 mm can have a high influence on the movement of
carbosulfan and carbofuran and there by influence the contamination also. In coastal
alluvial soil, the movement of carbosulfan and carbofuran was found to be higher
than in the laterite soil. The movement of carbofuran was comparatively slow than
carbosulfan. This is contrary to the results of Lalah and Wandiga (1996) rapid
movement of carbofuran could be noticed in soil. The movement of carbosulfan and
carbofuran in soil columns can be considered to be the net effect of adsorption
coefficient and water solubility. Carbosulfan with high adsorption coefficient and
water solubility moved down by virtue of the high water solubility while cabofuran
with low adsorption coefficient and low water solubility moved down due to less
adsorption. In both soils, at 200 µg level application of carbosulfan and 160 mL
water application resulted in residues in the leachate so it indicates that increased
concentration and increased rainfall can result in underground water contamination
especially in the coastal alluvial soil.
92
5.4 PERSISTENCE OF CARBOSULFAN
The effect of different treatments on the persistence of carbosulfan in laterite
and coastal alluvial soils were studied in the laboratory and under cropped condition
using EC and granule formulation .
5.4.1 Dissipation of Carbosulfan 25 EC in Laterite Soil
The dissipation of carbosulfan 25 EC in laterite soil is presented in Fig. 14.
The result showed that, T3 has the highest half life (10.53 days) ie 5 mg kg-1 level of
carbosulfan application in laboratory condition showed the maximum residue content.
The smallest half life (2.17 days) is for T4 in which 1 mg kg-1 carbosulfan 25 EC
was added in the cropped condition. The half life of T4, T5 and T6 (1, 2.5 and 5 mg
kg-1 under cropped condition respectively) were small compared to T1, T2 and T3 (1,
2.5 and 5 mg kg-1 under laboratory condition respectively). Thus, the result showed
that, in the cropped condition, carbosulfan was dissipated at a faster rate than the
laboratory condition. This may be due to the assimilation by crop, degradation by
microbes or by certain rhizospheric effects. This result adheres to the reports of
George et al. (2009) that the half life obtained for endosulfan under the laboratory
condition was comparatively higher than the actual field condition which they
attributed to the lower rate of exposure of the pesticide to environmental conditions
like sunlight, temperature and wind.
5.4.2 Dissipation of Carbosulfan 25 EC in Coastal Alluvial Soil
The dissipation of carbosulfan 25 EC in coastal alluvial soil is depicted in
Fig. 15. The result revealed that, T6 representing 5 mg kg-1 level in the cropped
condition had the highest half life (5.13 days) compared to all other treatments. The
smallest half life (2.35 days) was showed by T1 representing 1 mg kg-1 level in the
laboratory condition. In coastal alluvial soil, the EC formulation showed higher half
life in the cropped condition than the laboratory condition. It is contrary to the result
of laterite soil. This may be due to the higher organic matter content of coastal
93
Fig. 14. Half life of carbosulfan 25 EC in laterite soil under laboratory and cropped conditions
Fig. 15. Half life of carbosulfan 25 EC in coastal alluvial soil under laboratory and cropped
conditions
0
2
4
6
8
10
12
T1 T2 T3 T4 T5 T6
Day
s
Treatments Half Life
T1- 1 mg kg-1 in laboratory condition, T2- 2.5 mg kg-1 in laboratory condition , T3- 5 mg kg-1 in laboratory condition, T4- 1 mg kg-1 in cropped condition, T5- 2.5 mg kg-1 in cropped condition T6- 5 mg kg-1 in cropped condition
0
1
2
3
4
5
6
T1 T2 T3 T4 T5 T6
Day
s
Treatments Half Life
T1- 1 mg kg-1 in laboratory condition, T2- 2.5 mg kg-1 in laboratory condition , T3- 5 mg kg-1
in laboratory condition, T4- 1 mg kg-1 in cropped condition, T5- 2.5 mg kg-1 in cropped condition T6- 5 mg kg-1 in cropped condition
alluvial soil. The coastal alluvial soil had comparatively higher organic matter
(0.84 %) content than laterite soil (0.41 %) in the natural condition itself. In the
cropped condition as organic matter is again added might have again increased and
lead to more adsorption of carbosulfan on its surface and hence more retention and
persistence. This result is in corroboration with the earlier findings obtained in the
study conducted for chlorpyrifos by George et al. (2007) where higher application of
organic manure increased the persistence of chlorpyrifos. Similarly, the high organic
matter and low pH increased the persistence of fipronil in soil (Mandal and Singh,
2013 ). But this is contrary to the result obtained for George et al. (2009) that
laboratory condition resulted in a higher half life for endosulfan than cropped
condition due to lower exposure to environmental conditions such as temperature,
light etc.
5.4.3 Dissipation of Carbosulfan Granules in Laterite Soil
The dissipation of carbosulfan granules in laterite soil is represented in Fig.
16. It showed that, T3 had the highest half life (11.5 days) and T4 had the lowest half
life (3.26 days) period. So, 1 mg kg-1 application in the cropped condition showed
the lowest half life and 5 mg kg-1 application in the laboratory condition showed the
highest half life. This is similar to the case of carbosulfan 25 EC in the present study.
Here, the variation among T1, T2 and T3 were very small compared to the case of EC
formulation. But in cropped condition, the degradation was comparatively faster than
the laboratory condition. The half lives obtained for granules were higher than EC
formulation. This result is similar to the result of Liu et al. (2015) for chlorpyrifos in
which the granule formulation had half lives of 4.1 to 4.36 times more than the EC
formulation and he mentioned that the granules release the pesticides in a controlled
manner so there may be low risk of environmental pollution too.
94
Fig. 16. Half life of carbosulfan granules in laterite soil under laboratory and cropped conditions
Fig. 17. Half life of carbosulfan granules in coastal alluvial soil under laboratory and cropped
conditions
0
2
4
6
8
10
12
14
T1 T2 T3 T4 T5 T6
Day
s
Treatments Half Life
T1- 1 mg kg-1 in laboratory condition, T2- 2.5 mg kg-1 in laboratory condition , T3- 5 mg kg-1 in laboratory condition, T4- 1 mg kg-1 in cropped condition, T5- 2.5 mg kg-1 in cropped condition T6- 5 mg kg-1 in cropped condition
0
2
4
6
8
10
12
T1 T2 T3 T4 T5 T6
Day
s
TreatmentsHalf Life
T1- 1 mg kg-1 in laboratory condition, T2- 2.5 mg kg-1 in laboratory condition , T3- 5 mg kg-1 in laboratory condition, T4- 1 mg kg-1 in cropped condition, T5- 2.5 mg kg-1 in cropped condition T6- 5 mg kg-1 in cropped condition
5.4.4 Dissipation of Carbosulfan Granules in Coastal Alluvial Soil
The dissipation of carbosulfan granules in coastal alluvial soil represented in Fig. 17.
The result revealed that, the highest half life was obtained for T3 and the lowest is for T4
formulation. T3 represents the 5 mg kg-1 level of carbosulfan application in the laboratory
condition and T4 represents the 1 mg kg-1 application of carbosulfan granules in cropped
condition. In this case, the cropped condition showed relatively shorter half life period than the
laboratory condition in coastal alluvial soil. This result is contrary to the result of carbosulfan 25
EC in coastal alluvial soil, in which the cropped condition showed longer half life than
laboratory condition. This may due to the inherent difference between the two formulations.
The persistence of carbosulfan can be summarized as follows : the half lives obtained for
granule formulations were comparatively higher than the EC formulation. This may be due to the
change in the release of carbosulfan from the two formulations. When we are applying the EC
formulation, we are directly applying it to the soil as solution while when we are adding the
granules it may take some times for the granules to disintegrate and to release the pesticide. In
laboratory condition, the half life was found to be more than the cropped condition and this may
be due to the rhizospheric effect and assimilation by plants in the cropped condition. In coastal
alluvial soil, the half life in the cropped condition was comparatively higher than the laterite soil
and this can be due to the higher organic matter in the coastal alluvial soil than the laterite soil
and thus resulted in high adsorption and there by retention of the pesticide for longer period. In
laboratory condition, the laterite soil has relatively higher persistence than coastal alluvial soil. It
can be due to better degradation of carbosulfan in coastal alluvial soil due to better microbial
population than laterite as a result of high organic matter content. Similar result was reported by
Sahoo et al. (1998) in which, the carbosulfan degradation was much faster in non sterilized
media than the sterilized media. With increase in the concentration of the carbosulfan treatment
from 1 to 5 mg kg-1 levels, the persistence was found to be more which can
95
be presumably due to the lethal effect of carbosulfan on microbes and there by the consequent
decreasede rate of microbial degradation .
5.5 DEGRADATION OF CARBOSULFAN IN SOIL
The study of the metabolism of carbosulfan in laterite and coastal alluvial soil under the
laboratory and cropped conditions was done using EC and granule formulation. The metabolites
formed were monitored on the 0, 1, 3, 5, 7, 10, 15, 20, 30 and 45th day.
5.5.1 Metabolism of Carbosulfan 25 EC in Laterite Soil under Laboratory Condition and
Cropped Condition
The metabolism of carbosulfan 25 EC in the laterite soil under laboratory condition is
depicted in Figures. 18-20. It is seen that, from the 0th day itself the degradation of carbosulfan
started and along with that, the formation of carbofuran was noticed. The carbofuran
concentration was maximum on the 15th day, and along with this, the metabolites such as 3- keto
carbofuran and 3- hydroxy carbofuran were also formed but at 1 mg kg-1 level of treatment, the
concentration was too low and from 0- 5 mg kg-1 level, the concentration of these two
metabolites increased. At 1 and 2.5 mg kg-1 levels, the carbosulfan residues were found upto 30th
day and with increasing the treatment level to 5 mg kg-1, the residues were found upto 45th day
while the presence of the other two metabolites were found upto 45th day. The concentration of
3- keto carbofuran was found to be more than the 3- hydroxy carbofuran. Similar results were
reported by Nigg et al. (1985) in which, the carbosulfan application resulted in the formation of
carbofuran and 3 hydroxy carbofuran but the concentration of 3- hydroxyl carbofuran was very
low due to its low rate of formation or fast disappearance. Under cropped condition it is
presented in Figures. 21-23. The maximum carbofuran concentration was on 7th day and the
formation of the other two metabolites were very low in concentration.
96
Fig. 18. Degradation of carbosulfan 25 EC in laterite soil at 1 mg kg-1 level under laboratory condition
Fig. 19. Degradation of carbosulfan 25 EC in laterite soil at 2.5 mg kg-1 level under laboratory condition
*3-OH carbofuran indicates 3- hydroxy carbofuran
0
0.5
1
1.5
2
2.5
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3-Keto carbofuran
0
0.5
1
1.5
2
2.5
3
3.5
0 1 3 5 7 10 15 20 30 45
Re
sid
us
in
mg
kg-1
Days
Carbosulfan Carbofuran 3-OH carbofuran 3-Keto Carbofuran
Fig. 20. Degradation of carbosulfan 25 EC in laterite soil at 5 mg kg-1 level under laboratory condition
Fig. 21. Degradation of carbosulfan 25 EC laterite soil at 1 mg kg-1 level under cropped condition
*3-OH carbofuran indicates 3- hydroxy carbofuran
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3 OH carbofuran 3-Keto carbofuran
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran
Fig. 22. Degradation of carbosulfan 25 EC laterite soil at 2.5 mg kg-1 level under
cropped condition
Fig. 23. Degradation of carbosulfan 25 EC laterite soil at 5 mg kg-1 level under cropped condition
*3-OH carbofuran indicates 3- hydroxy carbofuran
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran
0
0.5
1
1.5
2
2.5
3
3.5
4
0 1 3 5 7 10 15 20 30 45
resi
du
es
in
mg
kg-1
Days
carbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran
5.5.2 The Metabolism of Carbosulfan 25 EC in Coastal Alluvial Soil under
Laboratory and Cropped Conditions
The metabolism of carbosulfan in coastal alluvial soil under laboratory
condition is depicted in Figures. 24-26. It is seen that a decreasing trend of the
carbosulfan from 0th day and the subsequent carbofuran formation from the 0th day
onwards. The carbofuran was maximum on 7th day . The formation of 3- keto
carbofuran and 3 hydroxy carbofuran were prominent at 1 and 2.5 mg kg-1 levels. The
maximum residues of 3- keto carbofuran was noticed on 30th day at these two levels
of treatment. At 5 mg kg-1 level of treatment, the maximum 3- keto carbofuran was
obtained on 20th day. The metabolites formed in coastal alluvial soil by application
of EC under cropped condition is illustrateded in Figures. 27-29. It is found that,
from the 0th day itself, the carbosulfan was decreasing and the carbofuran was
maximum on the 10th day. In this case also, the concentration of the other two
metabolites were very low.
5.5.3 Metabolism of Carbosulfan Granules in Laterite Soil under Laboratory
and Cropped Conditions
The application of granules in the laterite soil under laboratory study is
presented in Figures. 30-32. The result showed that, the carbosulfan residues
increased from 0th day to 7th day and then decreased. The carbofuran was found from
the 0th day itself and the was maximum on the 10th day. The formation of 3 hydroxy
carbofuran and 3 keto carbofuran were also noticed and the second one formed
comparatively higher in concentration. At 1 and 2.5 mg kg-1, level the maximum
residues of 3 keto carbofuran were noticed on the 30th day and at 5 mg kg-1 level, the
maximum residues were found on the 15th day. Under cropped conditions as
illustrated in Figures. 33-35, the residues were found to increase which may be due to
the controlled release of the carbosulfan from granules and on the 10 th day, the
97
Fig. 24. Degradation of carbosulfan 25 EC in coastal alluvial soil at 1 mg kg-1 level under laboratory condition
Fig. 25. Degradation of carbosulfan 25 EC in coastal alluvial soil at 2.5 mg kg-1 level under laboratory condition
*3-OH carbofuran indicates 3- hydroxy carbofuran
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3-Keto carbofuran
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3-Keto carbofuran
Fig. 26. Degradation of carbosulfan 25 EC in coastal alluvial soil at 5 mg kg-1 level under laboratory condition
Fig. 27. Degradation of carbosulfan 25 EC in coastal alluvial soil at 1 mg kg-1 level
under cropped condition
*3-OH carbofuran indicates 3- hydroxy carbofuran
0
0.5
1
1.5
2
2.5
3
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
es
in m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3-Keto carbofuran
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran
Fig. 28. Degradation of carbosulfan 25 EC in coastal alluvial soil at 2.5 mg kg-1 level under cropped condition
Fig. 29. Degradation of carbosulfan 25 EC in coastal alluvial soil at 5 mg kg-1 level under cropped condition
*3-OH carbofuran indicates 3- hydroxy carbofuran
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 1 3 5 7 10 15 20 30 45 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran
0
0.2
0.4
0.6
0.8
1
1.2
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran
Fig. 30. Degradation of carbosulfan granules in laterite soil at 1 mg kg-1 level under laboratory condition
Fig. 31. Degradation of carbosulfan granules in laterite soil at 2.5 mg kg-1 level under laboratory condition
*3-OH carbofuran indicates 3- hydroxy carbofuran
0
0.05
0.1
0.15
0.2
0.25
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3 OH carbofuran 3-Keto carbofuran
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3-Keto carbofuran
Fig. 32. Degradation of carbosulfan granules in laterite soil at 5 mg kg-1 level under laboratory condition
Fig. 33. Degradation of carbosulfan granules in laterite soil at 1 mg kg-1 level under cropped condition
*3-OH carbofuran indicates 3- hydroxy carbofuran
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3-Keto carbofuran
0
0.1
0.2
0.3
0.4
0.5
0.6
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Dayscarbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran
Fig. 34. Degradation of carbosulfan granules in laterite soil at 2.5 mg kg-1 level under cropped condition
Fig. 35. Degradation of carbosulfan granules in laterite soil at 5 mg kg-1 level under cropped condition
*3-OH carbofuran indicates 3- hydroxy carbofuran
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 1 3 5 7 10 15 20 30 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran
carbofuran was maximum. In this case also, the concentrations of 3 keto and 3-
hydroxy carbofuran were very low in concentration.
5.5.4 Metabolism of Carbosulfan Granules in Coastal Alluvial Soil Under
Laboratory and Cropped Conditions
Metabolism of carbosulfan granules applied in coastal alluvial soils under
laboratory conditions is depicted in Figures. 36-38. The result revealed that,
concentration of carbosulfan increased from 0- 3rd day and then declined. Formation
of carbofuran increased and maximum amount was noticed on 7th day. Formation of
the other two metabolites were at very low concentrations. Application under
cropped conditions (Figures. 39-41) also showed an initial increase in carbosulfan
residue upto 3rd day and then a decline along with the formation of carbofuran, 3 keto
and 3 hydroxy carbofuran at comparatively higher concentrations in cropped
condition than under laboratory condtion. These result were similar to the findings of
Pal et al. (2005) on the effect of organic matter and nutrient addition on the faster
degradation of pesticides in soil by enhancing the microbial growth and enzyme
activity.
5.6 EFFECT OF CARBOSULFAN ON SOIL ORGANISMS
The effect of carbosulfan on the microbial population of the two soils were
studied using EC and granule formulation each at normal (250g ai ha-1 ) and at double
(500 g ai ha-1) doses. A control or pre treatment sample was also maintained to
assess the relative inhibition/ enhancement of microbial population by the treatments.
5.6.1 Effect of Carbosulfan on the Microbial Population in Laterite Soil
The result of the effect of carbosulfan treatment on the bacterial population in
laterite soil is presented in Fig. 42. It is seen that, an increase in the population by
application of EC formulation in the normal dose. A slight increase was observed by
double dose application of EC but was statistically on par with control population.
Granular application resulted in a decline in the bacterial population at both the doses.
98
Fig. 36. Degradation of carbosulfan granules in coastal alluvial soil at 1 mg kg-1 level under laboratory condition
Fig. 37. Degradation of carbosulfan granules in coastal alluvial soil at 2.5 mg kg-1 level under
laboratory condition
*3-OH carbofuran indicates 3- hydroxy carbofuran
0
0.1
0.2
0.3
0.4
0.5
0.6
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3-Keto carbofuran
0
0.1
0.2
0.3
0.4
0.5
0.6
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3-Keto carbofuran
Fig. 38. Degradation of carbosulfan granules in coastal alluvial soil at 5 mg kg-1 level under
laboratory condition
Fig. 39. Degradation of carbosulfan granules in coastal alluvial soil at 1 mg kg-1 level under
cropped condition
*3-OH carbofuran indicates 3- hydroxy carbofuran
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3-Keto carbofuran
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran
Fig. 40. Degradation of carbosulfan granules in coastal alluvial soil at 2.5 mg kg-1 level under
cropped condition
Fig. 41. Degradation of carbosulfan granules in coastal alluvial soil at 5 mg kg-1 level under cropped condition
*3-OH carbofuran indicates 3- hydroxy carbofuran
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
mg
kg-1
Days
carbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran
0
0.2
0.4
0.6
0.8
1
1.2
0 1 3 5 7 10 15 20 30 45
Re
sid
ue
s in
m
g kg
-1
Days
carbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran
Fig. 42 Effect of carbosulfan on the microbial population of laterite soil Bacterial population is in 106 cfu mL-1, fungi and actinomycetes population in 104 cfu mL-1 and arthropod population in per kilo gram
soil
0
2
4
6
8
10
12
14
Carbosulfan 25 EC -
normal dose
Carbosulfan 25 EC
at double dose
Carbosulfan G at
normal dose
Carbosulfan G at
double dose
Control
Po
pu
lati
on
Treatments
Bacterial Population Fungal Population Actinomycetes Population Arthropod Population
Increase in the concentration of EC and granules resulted in a decline in the bacterial
population. This is contrary to the report of by Zhou et al. (2012) on the effect of
butachlor and carbofuran on methanogens. The study showed a slight increase in the
methanogens by application of butachlor and carbofuran in paddy soil. The higher
concentration of the butachlor and carbofuran significantly inhibited the methanogen
population.
A decline in the fungal population was noted by the application of carbosulfan
EC and granules at normal dose and with increasing the concentration, a slight
increase in the population (especially with granules in double dose) was noted than
the normal dose but it was not significant compared to the control soil. In the case of
actinomycetes, the normal dose application of granules had a significant positive
effect on the population and all other treatments decreased the population. The
arthropod population in the soil was decreased by normal dose of carbosulfan
application and it was further decreased by double dose of application.
5.6.2 Effect of Carbosulfan on the Microbial Population in Coastal Alluvial Soil
The effect of carbosulfan on the microbial population in coastal alluvial soil
presented in Fig. 43. Which indicated a marked increase in the bacterial population
by application of EC and granule forms in the normal dose. With increase in the
concentration of both formulations, a decline in the bacterial population was noticed.
The fungal population in the soil was increased by application of EC in normal dose
and all other treatments decreased the population of fungi. In coastal alluvial soil,
normal dose of both formulations of carbosulfan resulted in an increase in the
population dynamics of actinomycetes while that was reduced by the application of
the formulations in double dose. The arthropod population also reduced with all the
carbosulfan treatments. This result is similar to the findings of (Fountain et al., 2008)
that application of chlorpyrifos can result in the reduction of arthropod and predatory
spider populations.
99
Fig. 43 Effect of carbosulfan on the microbial population of coastal alluvial soil Bacterial population is in 106 cfu mL-1, fungi and actinomycetes population in 104 cfu mL-1 and arthropod population in per
kilo gram soil.
0
5
10
15
20
25
Carbosulfan 25 EC -
normal dose
Carbosulfan 25 EC at
double dose
Carbosulfan G at
normal dose
Carbosulfan G at
double dose
Control
Po
pu
lati
on
Treatments
Bacterial Population Fungal Population Actinomycetes Population Arthropod Population
So it can be summarized that, the application of carbosulfan EC and granules
in normal dose created an increase in the bacterial and actinomycetes population. The
fungal population in the coastal alluvial soil was also increased by normal dose of EC
but it created detrimental effect on other organisms. The double dose of application
generally created a significant reduction in the microbial population. The results
revealed that, carbosulfan had an inhibitory effect on arthropod population. It could
be understood from the study that, the different formulations had different effect on
the microbes, which is similar to the result of Holockova et al. (2013) in which the
different formulations of triazole induced different toxic effects on the bovine culture.
Likewise according to Kumar et al. (2002), application of chlorothalonil resulted in
significant reduction in the microbial mass. A slight increase in the pH of the soil
was observed after 24 h of carbosulfan application which then remained stable upto
3rd day and the preferential change in the pH could also have affected the microbial
population in the carbosulfan treated soil.
100
Summary
6. SUMMARY
Pesticides are inevitable in modern intensive agriculture, due to replacement
of traditional varieties with high yielding varieties which are more prone to pest and
disease infestation, which inturn necessitates timely pest control operations for
obtaining optimum expected yield. Among the numerous approaches for managing
the pest, farmers give preference to chemical method, since it provide quick and
efficient result together with its easy availability. An ideal pesticide should disappear
after its pesticidal action and thus it should not produce any harmful effect on
environment or any organism other than the target one either directly or indirectly.
Among the various carbamate pesticides, carbosulfan is used as a substitute
for carbofuran, the use of which was banned in Kerala due to its extreme lethal effect.
Carbofuran comes under extremely toxic category while carbosulfan comes under
highly toxic category. So the handling of carbosulfan is comparatively safer than
carbofuran. But upon degradation of carbosulfan, carbofuran was formed and the
insecticidal toxicity of carbosulfan was mostly due to this carbofuran than the
carbosulfan. The carbofuran degradation resulting in the formation of 3- hydroxy
carbofuran and 3- keto carbofuran which also have toxicological importance. In this
context, a study was conducted to understand the persistence and transformation of
carbosulfan in two major soil types of Kerala viz., Laterite and coastal alluvial soils
by assessing the persistence, transformation and effect on soil organisms as
influenced by the type of formulation and soil factors.
The two soil types, laterite and coastal alluvial were collected from
representative types available Vellayani and Kazhakkoottam, respectively. Their
physico chemical properties were analyzed. A suitable method was validated for the
single step estimation of multiple residues (Carbosulfan + 3 metabolites) in soil by
following modified QuEChERS method.
101
The mobility of carbosulfan was studied by packed soil column method using
100, 150 and 200 µg level of pesticide and elution with 20, 40, 80 and 160 mL of
water equivalent to 50, 100, 200 and 400 mm of rainfall in the field condition. The
persistence study was conducted by application of both carbosulfan 25 EC and
granules at a concentration of 1, 2.5 and 5 mg kg-1 level in laboratory condition and
cropped (growbag) condition with chilli (var, Ujwala) as test crop. The metabolite
formation was studied using the same soil that used for persistence. The residues
were estimated and quantified by using LC-MS/ MS method. The effect on soil
organisms were studied by applying carbosulfan EC and granules at normal (250g ai
ha-1) and double (500 g ai ha-1) doses. The data were statistically analyzed and the
results were summarized below.
1. The physico chemical analysis of the two soils indicated that laterite soil
comes under sandy loam while the coastal alluvial soil comes under loamy
sand. The WHC and porosity of laterite soil was more than coastal alluvial
soil. The two soils were strongly acidic and the EC and CEC of coastal
alluvial soil were found to be higher than that of the laterite soil. The organic
matter content of laterite soil was 0.41 per cent and that of coastal alluvial soil
was 0.84 per cent. The primary and secondary nutrients were comparatively
more for coastal alluvial soil.
2. The efficiency of extraction of carbosulfan and its metabolite from soil was
standardized through recovery experiment. The modified QuEChERS method
with extraction using acetonitrile followed by dispersive solid phase clean up
was found to be suitable. The analytical procedures gave good recovery for
the residues ranging from 80- 99.20 per cent and 88.4- 100.6 per cent in
laterite soil and coastal alluvial soils respectively and relative standard
deviation ranged from 6.9- 11.6 and 4.5- 8.4 for laterite and coastal alluvial
soils respectively.
102
3. The mobility study showed that, with an increase in the volume of water used
for leaching, more migration occurred to the lower layers. Carbofuran was
also detected along with carbosulfan, but was present only at lower
concentration compared to carbosulfan. The extent of migration of
carbosulfan in coastal alluvial soil was found to be more than the laterite soil.
4. The mobility study revealed that, the texture has an important role in the
movement of residues because the coastal alluvial soil having more total sand
which being more inert and more porous showed more migration due to better
infiltration of carbosulfan along with water.
5. The increased concentration of carbosulfan along with more volume of water
used (160 mL equivalent to high rainfall) for elution significantly increased
the migration tendency and there by the residues detected in the leachate also.
6. The half lives (t1/2) of carbosulfan 25 EC in the laterite soil when applied at 1,
2.5 and 5mg kg-1 levels were 5.08, 7.69 and 10.53 days, respectively in the
laboratory condition, while in the cropped condition they were 2.17, 4.60 and
5.24 days, respectively.
7. In coastal alluvial soil, application of carbosulfan 25 EC at 1, 2.5 and 5 mg
kg-1 level resulted in half lives of 2.35, 2.91 and 4.96 days, respectively in the
laboratory condition and 2.95, 4.59 and 5.13 days, respectively, under cropped
condition. So, half lives were more under cropped situation, this may be due
to more retention of carbosulfan in this soil due to increased adsorption under
the influence of more organic matter.
8. The persistence of carbosulfan granule in the laterite soil at the same level of
treatment resulted in half lives of 9.88, 10.50 and 11.50 days in the laboratory
condition and 3.26, 5.16 and 7.30 days, respectively in cropped condition.
9. In coastal alluvial soil, the half lives of carbosulfan granules were 8.99, 9.45
and 10.45 days in the laboratory condition and 5.70, 6.50 and 9.80 days,
103
respectively in the cropped condition at 1, 2.5 and 5 mg kg-1 level of
application.
10. The dissipation study revealed that by applying EC formulation in soil, the
level of residues declined from the 1st day itself due to degradation, while for
granules, an initial increase in the residue level (maximum upto 7th day for
laterite and 3rd day for coastal alluvial soil) was observed and then declined.
The granule formulation had higher persistence than the EC formulation in
both soils.
11. The half life of carbosulfan 25 EC was higher in laboratory condition than
cropped condition in laterite soil, presumably due to assimilation by plants,
degradation by microbes, or photo degradation etc.
12. The half life of carbosulfan 25 EC in coastal alluvial showed a longer half life
in the cropped condition than the laboratory condition which might be due to
the high organic matter content, which can absorb and retain the carbosulfan
for more longer time and thereby increase its persistence.
13. The results showed that organic matter has a significant influence on the
persistence of carbosulfan because organic matter in a certain level
accelerated the process of degradation of carbosulfan that is why in the
laboratory condition coastal alluvial soil showed faster degradation than
laterite soil. But beyond a certain level, there may be a chance of increased
persistence by increased adsorption by organic matter in soil.
14. In granular formulation, the half life obtained with coastal alluvial soil was
more under cropped condition, than for laterite soil, indicating its higher
persistence in coastal alluvial soil, with crop.
15. The study on degradation of carbosulfan revealed the formation of carbofuran
from the 0th day of treatment.
16. The degradation of carbosulfan resulted in formation of carbofuran, which
got further degraded to 3-keto carbofuran and 3- hydroxy carbofuran. The
104
concentration of metabolite formed is in the order of carbofuran> 3-keto
carbofuran> 3-hydroxy carbofuran in the two soils.
17. The normal dose application of carbosulfan 25 EC increased the bacterial
population in the two soils. In coastal alluvial soil, the normal dose of
granules and EC increased the bacterial and actinomycetes population.
18. The fungal population in the soil was increased by normal dose of EC
application in coastal alluvial soil and the arthropod population was decreased
by all carbosulfan treatments in the two soils.
19. The double dose application of carbosulfan has decreased the population of
microbes significantly.
The study concluded that the nutrient content, CEC and OM content of soils were
high for the coastal alluvial soil. In laterite soil the WHC, porosity etc were higher
than coastal alluvial soil. The mobility of carbosulfan EC was found to be higher in
the coastal alluvial soil. A higher dose application of carbosulfan and subsequent
elution with high volume of water resulted in deep migration of carbosulfan beyond
the soil column to the leachate itself. The persistence study revealed that, granule
formulation has a higher half life in both the soils. The half life of carbosulfan 25 EC
in cropped condition was less than that in the laboratory condition in laterite soil
while in coastal alluvial soil cropped condition showed, increased half life than the
laboratory condition due to the influence of organic matter. The metabolite formation
showed the formation of carbofuran on the 0th day itself and the formation of 3
hydroxy carbofuran metabolite was found to be very less than 3 keto carbofuran. The
effect of carbosulfan on soil organism showed that the double dose of application of
both granules and EC resulted in an inhibition in the microbial population, while the
normal dose of the two formulations resulted in a stimulatory effect on certain
microbial population.
105
FUTURE LINE OF WORK
Distribution and fate of applied pesticide in soil, leachate and crop need to be
studied for commonly used soil pesticides.
Impact of soil applied pesticides on soil organisms and the biochemical
mechanisms for the promotion / decline in population need to be assessed at
molecular level.
The possibilities of ground water contamination by commonly used pesticides
in different soils should be studied.
106
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*Original not seen
121
PERSISTENCE AND TRANSFORMATION OF CARBOSULFAN
IN LATERITE AND COASTAL ALLUVIUM SOILS OF KERALA
AND ITS EFFECT ON SOIL ORGANISMS
by
DHANYA. M. S
(2014-11-152)
Abstract of the thesis
Submitted in partial fulfilment of the
requirements for the degree of
MASTER OF SCIENCE IN AGRICULTURE
Faculty of Agriculture
Kerala Agricultural University
DEPARTMENT OF SOIL SCIENCE AND AGRICULTURAL CHEMISTRY
COLLEGE OF AGRICULTURE
VELLAYANI, THIRUVANANTHAPURAM-695 522
KERALA, INDIA
2016
ABSTRACT
The study entitled ‘Persistence and transformation of carbosulfan in laterite
and coastal alluvium soils of Kerala and its effect on soil organisms’ was conducted
at Department of Soil Science and Agricultural Chemistry and the laboratory
attached to the All India Network Project (AINP) on Pesticide Residues, College of
Agriculture, Vellayani, Thiruvananthapuram, Kerala during 2015-16. The main
objectives of the experiment were to study the persistence, mobility and
transformation of carbosulfan in laterite and coastal alluvium soils of Kerala (in
cropped and non cropped situation) and to assess its effect on soil organisms. Laterite
and coastal alluvial soils were collected from Vellayani and Kazhakkoottam
respectively. The physico-chemical analysis of the soils were done which revealed
that coastal alluvial soils had an organic matter content of 0.84 per cent while laterite
had only 0.41 per cent. The primary and secondary nutrients were comparatively
higher for coastal alluvial than laterite soil. The method for the estimation of
carbosulfan residues from the soils were validated at 0.05, 0.25 and 0.50 µg g-1 level
of carbosulfan. Modified QuEChERS method with acetonitrile as extracting solvent
and Primary Secondary Amine (PSA) sorbent for clean up was found to be suitable
for the estimation of carbosulfan from the soil.
Mobility of carbosulfan was assessed by loading 3 levels viz., 100, 150 and
200 µg of carbosulfan 25 EC separately on top of soil columns in PVC pipes and
eluting with 20, 40, 80 and 160 mL of water. In the laterite soil, carbosulfan moved
down the soil column and resulted in residue levels ranging from 1.50-0.04, 2.29-0.27
and 3.55-0.05 mg kg-1 at 100, 150 and 200 µg levels, respectively when eluted with
water. In the coastal alluvial soil, the corresponding residues ranged from 1.78-0.32,
2.20-0.51 and 3.07-0.72 mg kg-1 at 100, 150 and 200 µg level after elution with
water. The residues found on the leachate ranged from 0.001-0.01mg kg-1 for laterite
and 0.001-0.03 mg kg-1 for coastal alluvial soil.
The persistence of carbosulfan in the laterite and coastal alluvial soils under
laboratory and cropped (grow bag with chilli Ujwala variety) conditions
122
was studied using two formulations viz., Emulsifiable Concentrate (EC) and granular
formulations each at 1, 2.5 and 5 mg kg-1 levels. The half lives (t1/2) of carbosulfan 25
EC in the laterite soil when applied at 1, 2.5 and 5mg kg-1 levels were 5.08, 7.69 and
10.53 days respectively in the laboratory condition, while in the cropped condition
they were 2.17, 4.60 and 5.24 days, respectively. In coastal alluvial soil, application
of carbosulfan 25 EC at 1, 2.5 and 5 mg kg-1 level resulted in half lives of 2.35, 2.91
and 4.96 days respectively in the laboratory condition and 2.95, 4.59 and 5.13 days
respectively under cropped condition. The persistence of carbosulfan granule in the
laterite soil at the same level resulted in half lives of 9.88, 10.50 and 11.50 days in the
laboratory condition and 3.26, 5.16 and 7.30 days respectively in cropped condition.
In coastal alluvial soil, the half lives of carbosulfan granules were 8.99, 9.45 and
10.45 days in the laboratory condition and 5.70, 6.50 and 9.80 days respectively in
the cropped condition at 1, 2.5 and 5 mg kg-1 level of application.
The three toxicologically important metabolites of carbosulfan viz.,
carbofuran, 3-hydroxy carbofuran and 3-keto carbofuran were monitored and the
metabolite concentration was in the order of carbofuran > 3-keto carbofuran > 3-
hydroxy carbofuran in the two soils.
The effect of EC and granular formulation of carbosulfan on the microbial
load was monitored after normal (250 g ai ha-1) and double (500 g ai ha-1) dose and
found that in laterite soil the bacterial population increased to 9.45 x 106 cfu g-1 soil
from the control population (6.86 x 106 cfu g-1) at normal dose of EC formulation.
Granule application in the normal dose resulted in a higher population of
actinomycetes (6.59 x 104 cfu g-1) than control (4.95 x 104 cfu g-1). In the coastal
alluvial soil, application of EC and granules in the normal dose increased the bacterial
population to 19.53 x 106 cfu g-1 and 20.35 x 106 cfu g-1 soil respectively from the
control population (11.74 x106 cfu g-1). The population of arthropods declined in the
two soils by carbosulfan treatment at both levels.
The study concluded that the mobility of carbosulfan was found to be higher
in the coastal alluvial soil compared to laterite soil. The persistence of
123
carbosulfan was higher in granular formulation than in EC in both soils.
Transformation of carbosulfan gives carbofuran as the major metabolite which on
further degradation gives 3-keto and 3- hydroxy carbofuran in soil. The normal dose
application of carbosulfan had certain positive effect on the soil organisms but the
double dose application resulted in a considerable reduction in the population of
microbes in the two soils.
124
Persistence and transformation of carbosiilfan in laterite and coastal alluvium
soils of Kerala and its effect on soil organisms
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Appendix
APPENDIX I
Calibration Curve of Standard Carbosulfan and its Metabolites
Calibration curve of carbosulfan
Calibration curve of carbofuran
Calibration curve of 3- hydroxy carbofuran
Calibration curve of 3- keto carbofuran
APPENDIX II
Chromatogram of Standard of Carbosulfan and its Metabolites at 0.005 mg kg-1
Chromatogram of carbosulfan and its metabolite at 0.005 mg kg-1 in laterite soil
APPENDIX III
Chromatogram of Recovery of Carbosulfan and its Metabolites from Laterite Soil
Recovery of carbosulfan and its metabolites at 0.01 mg kg-1 in laterite soil
Recovery of carbosulfan and its metabolites at 0.05 mg kg-1 in laterite soil
Recovery of carbosulfan and its metabolites at 0.25 mg kg-1 in laterite soil
Recovery of carbosulfan and its metabolites at 0.50 mg kg-1 in laterite soil
APPENDIX IV
Chromatogram of Recovery of Carbosulfan and its Metabolites from Coastal Alluvial Soil
Chromatogram of carbosulfan and its metabolites at 0.01 mg kg-1 in coastal alluvial soil
Chromatogram of carbosulfan and its metabolites at 0.05 mg kg-1 in coastal alluvial soil
Chromatogram of carbosulfan and its metabolites at 0.25 mg kg-1 in coastal alluvial soil
Chromatogram of carbosulfan and its metabolites at 0.50 mg kg-1 in coastal alluvial soil
APPENDIX V
Mass Spectra of Carbosulfan and its Metabolites at 0.01 mg kg-1
Mass spectra of carbosulfan and its metabolites at 0.01 mg kg-1