ADSORPTION AND MOBILITY OF PESTICIDES AND TRACE METALS WITH SOILS

AND CLAYS

RESUME

THESIS SUBMITTED FOR THE DEGREE OF

IN CHEMISTRY

BY

Miss. NUSRAT IQBAL M. Sc. M. Phil.

DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY

ALIGARH (INDIA)

July, 1987

RESUME

RESUME

Pesticides and chemical fertilizers are now being

extensively employed in India and abroad to achieve self suffi­

ciency in food crops. It has been revealed that the extensive

use of chemical fertilizers containing several unwanted heavy

metals are posing health hazard to human beings. It has also

been realized in recent past that a voluminous amount of work has

been reported on the use of sewage and industrial waste applica­

tion to agriculture land. It has been recognised that these

materials contain heavy metals such as Pb, Cd, Ni, Ag, Hg etc.

A great danger is involved due to the indiscriminate use of

these chemicals, a very little work has been done and, therefore,there

is a need to understand the specific role of these chemicals to

produce a healthy growth of plants and microbial activities in soil.

Pesticides and heavy metals show a variable adsorption in

soil as a result of variation in the environmental factors, such

as climatic influences, texture, clay mineral composition, moisture

level, alkalinity, salinity and pH etc. Therefore, it has been

established that the nature and extent of adsorption with soils

and clays affect their persistence, degradation, leaching and

translocation in soil environment which in turn control soil fer­

tility, plant growth, environmental pollution and soil behaviour.

(il)

The distribution of pesticides in soils after irrigation of rain­

fall is impoirtant as its effectiveness is dependent on its position

in soil profile. Their persistence and leachability in soils play

a vital role in determining their efficiency potential for crop

damage and environmental pollution. Therefore, it is important to

carry out investigations on some important pesticides and heavy

metals with clays and soils with a particular view to understand

their mechanism of adsorption and mobility to assess their effi­

ciency potential for their proper utilization and to avoid the risk

of soil pollution.

In view of this, it was considered worthwhile to undertake

studies on the "Adsorption and mobility of pesticides and trace

metals with soils and clays". The investigations reported in thesis

have been divided into the following chapters:

I, Studies on the mobility of some heavy metals through soil

by thin layer chromatography as influenced by organic

acids and bases,

II. Studies on the mobility of some pesticides as affected by

their chemical characteristics and some soil properties,

III, Adsorption of Cu , Pb * and Zn ^ with Ca- saturated

illite.

IV. Studies on the adsorption of methyl,2-benzimidazole car­

bamate (MBC) with clays as affected by various soil para­

meters.

(iii)

A concise account of the results achieved on the plan

mentioned above are as follows:

Chapter-I deals with the mobility of some heavy metals

namely, Pb, Cd, Ni, Hg and Ag in Aligarh soil in terms of R^-values

by soil thin layer cliromatography (soil TLC), The influence of

organic acids and their sodium salts, amino acids and organic bases

on mobility were studied.

It was found that the organic acids i.e.^fonnic, acetic and

oxalicj amino acids i.e, glycine, alanine and valine have increased

the mobility of heavy metals. However, no marked influence could

be observed in the case of organic bases i.e.^nicotine and pyridine.

The results have been explained on the basis of reaction mechanism

of complex formation, their stability, molecular size, pH and the

nature of the heavy metals in soil solutions,

Chapter-II deals with the mobility of some pesticides i,e,,

Fluchloralin, Formothion, Malathion and Thiometon through 3akit

sandy loam and Itwa silt loam soils have been studied by using

soil thin layer chromatography. The effect of soil organic matter

and their fractions (HA & FA), clay mineral, free sesquioxide

(AlpO, & Fe20v), soil pH and exchangeable cations was also under­

taken as their mobility factor.

It was found that the pesticides moved in the order:

Thiometon Maiathion> Formothion>Fluchloralin, The effects of

(iv)

all parameters studied have been found to decrease the pesticide

mobility to a considerable extent except the malathion which showed

an increase in its mobility upon the addition of humic acid to soils.

The results have been explained on the basis of chemical character­

istics of pesticide molecule and their adsorption characteristics

over soil colloids,

2+ 2+ 2+ Chapter-Ill deals with the adsorption of Cu , Pb and Zn

on Ca- saturated illite using the adsorption isotherms, Freundlich

equation and thermodynamic parameters. These results reveal that o o o

the binding strength of these ions follow the order Cu '*'>Pb '*'>Zn •*•

over Ca- illite surface and the adsorption decreases with rise in

temperature. From the Freundlich constants the adsorption capacity

(K) supports the above conclusions for the order of their preference

while the intensity factor (1/n) shows the reverse order of adsorp­

tion capacity of the metal ions. The thermodynamic parameters i.e.

AG, AH and AS"were also calculated which also confirmed our

earlier results,

Chapter-IV deals with the studies on the adsorption of

methyl,2-ben2imida2ole carbamate (MBC) at 30°C with Na- form of

montmorillonite, synthetic montmorillonite, illite, kaolinite and

dickite as affected by various soil parameters. The adsorption

isotherms were 'S' type in the case of Na- montmorillonite and Na-

synthetic montmorillonite and 'L' type for other clays under study

The adsorption isotherms were well represented by Freundlich

(v)

equation. The adsorption of MBC was in the order: Na- montmori-

llonite > Na- synthetic montmorillonite > Na- illite>Na- kaolinite>

Na- dickite. The values of adsorption capacity (K) is found to

decrease in the same order as in the case of adsorption isotherms

while the adsorption intensity (1/n) of MBC over montomorillonite

and synthetic montmorillonite is about half of the intensity for

kaolinite and dickite. It is suggested that there is strong compe­

tition for adsorption sites in montmorillonite and synthetic mont­

morillonite.

The adsorption was found to increase with increase in soil

organic matter, AlpO, and FepO^ contents and decrease with increase

in pH values and amount of sand contents.

ADSORPTION AND MOBILITY OF PESTICIDES AND TRACE METALS WITH SOILS

AND CLAYS

THESIS SUBMITTED FOR THE DEGREE OF

IN

GHBMLISTRY

BY

Miss. NUSRAT IQBAL M. Sc. M. Phil.

DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY

AUGARH (INDIA)

July, 1987

^ c ^ ^ ^556.p"

• 2 m 19W

T3443

DEDICATED TO MY

RESPECTED PARENTS

•>>. \*>i l t i t -

A L I G A R H M U S L I M U N I V E R S I T Y

M. Se. Ph. D.

Rcf. No

CHEMISTRY SECTION Z. H. COLLEGE OH ENGG. & TECH.

A. M. U. ALIGAKH.2020O1

Dated... 2§..7., 1987..

This i s to certify that the thesis

entitled,"Adsorption and mobility of pesticides

and trace metals with soi ls and clays" i s an

original work don© by Miss Nusrat Iqbal xinder my

supervision and i s suitable for submission for

the degree of Doctor of Philosophy .In Chemistry.

r-

3 ,11 ku^ ( SAMIULLAH KHAN )

Supervisor

ACKNOWLEDGEMENT

With utmost regard I express my deepest sense of

gratitude to Dr. Samiullah Khan, Reader, Chemistry Section,

Z.H, College of Engineering and Technology, Aligarh Muslim

University, Aligarh, for his valuable guidance, keen and

tireless assistance during the course 6f this work. 1 also

express my gratefulness to Professor A.U. Malik, Chairman,

Chemistry Section, Z.H. College of Engineering and Technology,

Aligarh Muslim University, Aligarh and Professor M.S. Ahmad,

Chairman, Department of Chemistry, Aligarh Muslim University,

Aligarh for providing research facilities,

I also wish to thank my colleagues and well wishers

for their cooperation and friendly behaviour.

( Nusrat Iqbal )

C O N T E N T S

Page

Goieral Introduction 1

Chapter - I : Studies on the mobility of some heavy metals through soi l by thin layer chromatography as influenced by organic acids and bases.

Introduction 57

Esqperimental 58

Results and Discussion - - — - - - - - - 65

References - - - - - - - - - - 83

Chapter - II: Studies on the mobility of some pesti­cides as affected by their chvnical characteristics and some soi l properties.

Introduction - - - - - - - - - - 85

Experimental - - - - - - - - - - 86

Results and Discussion - - - - - - - - - - 92

References - - - - - - - - - - 109

Chapter - III: Adsorption of Cu^*, Pb^* and Zn^* with Ca- saturated i l l i t e .

Introduction - - - - - - - - - - 110

Eacperimental — 111

Results and Discussion - - - - - - - - — 116

References - - - - - - - - - - 125

Chapter - IV: Studies on the mobility of methyl, 2-benzimidazole carbamate (MBC) with clays as affected by various soil para­meters.

Introduction - - . - - • . - - - - - 127

Experimental - - - — . . . . . . 127

Results and Discussion . . . . - „ . - . . 131

References 151

List of Papers 152

GENERAL INTRODUCTION

GENERAL INTRODUCTION

Soil is a product, resulting from disintegration and

decomposition of rocks, plants and animal materials. It possess­

es a distinct morphological, mineralogical and phyaicochemical

properties, resulting from certain inheritance, from its unique

position on the surface of the earth and from the environmental

factors existing at that position. However, according to Joffe

(1936) the soil may be defined as a natural body, differentiated

into horizons of mineral and organic constituents, usually un­

consolidated, of variable depth, which differs from the parent

material below in morphology, physical prope:rties and constitution,

checmial properties and composition and biological characteristics.

COMPOSITION OF SOIL

Soil is very complex in nature and consists of mainly five

important constituents namely mineral matter, organic matter,

soil water, soil air and living organisms.

MINERAL MATTERS:

The mineral matter is a product of physical and chemical

weathering of rocks consists of particles of varying sizes; those

in the finer state of subdivision 0.002 mm form the clay frac­

tion. The crystal structure of clay minerals have been discussed

2

in considerable detail by Grim,(1953); Marshall, (1964);

Van Olphen, (1963). Extensive studies of X-ray diffraction

patterns have revealed that clay is crystalline in nature and

composed of few simple building units (Donahue, 1977). The

first is a tetrahedron of four oxygen atoms surrounding a central

cation (usually Si * or Al ) and the second unit consists of

octaiiedron of six oxygens (or hydroxyls) around a large cation

3+ 2+ 2+ 3+

wiiich is most commonly Al , Mg , Fe or Fe combination of

these structural units gives rise to the structure of the clay

minerals. Various types of clay minerals are made up of some basic

arrangements of tetrahedra and octahedra namely, 1:1 and 2:1

arrangements. Some important and most frequently found clay

minerals are: montmorillonite, illite, vermiculite, chlorite,

kaolinite and amorphous clays. Structures of some important clay

minerals are given in Figs, 1 and 2^ The cation exchange, surface

areas and basic unit arrangements of the clay minerals and amor­

phous materieils are given in Table-I,

Montmorillonite:

Montmorillonites are swelling and sticky clays. They have

2:1 arrangement in which a single tetrahedral layer joined to each

side of the octahedral layer in sandwitch fashdon by sharing of

oxygen atoms. Some important references associated with the

investigations on the montomorillonite are: Hofmann et al, (1933);

SILICA SHEET W^m^^Mi

Si02

02 (OH)

(OH)

EXTERNAL ADSORPTIVE SURFACES

SILICA SHEET

ALUMINA SHEET'W

i.

CRYSTAL UNIT 7.1

DISTANCE FIXED LITTLE OR NO ADSORPTION

CRYSTAL UNIT

I (a l DIAGRAMMATIC EDGE VIEW OF KAOLlNITt SHOWING TWO COMPLETE LAYERS. THE RESPECTIVE CfSTAL UNITS ARE BOUND TO EACH OTHER TIGHTLY BY AN OXYGEN-HYDROXYL LINKAGE, THEREBY GIVING A RESTRICTED AND NON-EXPA^JDING LATTICE. THE ADSORPTIVE CAPACITY IS LIMITED.

'2(0ft)j

LXTERNAL ADSORPTIVE

SURFACES

510,

H j O

SiO,

^ ' ^2 SILICA SHEET

A, ^ ^ Z ^ A L U M I N A S H E E T ; ^ ^

SILICA SHEET

i+EXCHANGEABLE .S JCAIiONS l.._

SILICA SHEET

^ALUMirJA SHEET/

SILICA SHEET T I I

. . .1- -

I I

1(c ) ILLITE HAS THE SAME GENERAL STRUC­TURAL ORGANIZATION AS MONTMORIL-LONITE EXCEPT IN RESPECT TO THE LINKAGES BETWEEN THE CRYSTAL UNITS. HERE K ATOMS SUPPLY ADDITIOhJAL CON­NECTING LINKAGES BETWEEN THE CRYS­TAL UNITS, THUS SUPPLEMENTING THE OXYGEN BONDING. THE EXPANSlOfJ IS SHARPLY LESSENED BY K LINKAGES AND ADSORPTIVE CAPACITY OF THE CLAY LOWERED,

CRYSTAL UNIT 9.3 A

DISTANCE VARIABLE INTERNAL ADSORPTIVE SURFACES

CRYSTAL UNIT

K b ) DIAGRAMMATIC EtXiE Vl tW OP MONTMORILLONITE SHOWING TWO COMPLETE LAYERS. THE RESPECTIVE CRYSTAL UtJITS ARE LOOSELY BOUfJD TO ONE ANOTHER BY WEAK OXYGEN LINKAGES WHICH ALLOW WIDE EXPANSION OF THE LATTICE. THERE IS HIGH INTLRNAL AUSORPTION OF WATER AND CATIONS,

FIG. I

o o o o

TETnAHEDRAL SILICON SHLET

W /r /' ^'K J''^

OCTAHEDRAL GIBBSITE LHEET

c-axis I I I I I I

OCTAHEDRAL SHEET

TETRAHEDRAL SHEET

HYDROGEN BONDING

— 6

+ 12

y \ y \ ^ (y 6 "^ Xf ^ ^ 4 0 + 2 (OH) - l O

b-axis"*

? ' ' 0 KAOLINITE. A I 1 LAYER SILICATE MINERAL

4 Si

6 0

NET CHARGE

+ 16

- 1 2

4,~c^ u' ' W ^ -

n H^o EXCHANGEADLE CATIONS

2 ( c ) ILLITE STRUCTURE IS SIMILAR TO ? (b ) EXCEPT THAT THE ELECTRICAL IMBALANCE IS SET RIGHT OY THE PRESENCE OF K lOrJS SITUATED QETWtEtJ ADJACENT LAURS LO THAT THE NET CHARGE IS O.

14 A°

I I Tl/AMI !>RAl

sHt i r

c-axis OCTAHEDRAL

SHEET

TETRAHEDRAL SHEET

OC) O O ^ , ^ 0 -

.uir b - a x i b - *

6 0 4 (Si,

4 0 + 2

4 ( A I ,

4 0 + 2

4 SI 6 0

Al)

(OH)

Ft.Mrf)

(OH)

NET CHARGE

- 1 2 + 16

- 1 0

+ 12

- 1 0

+ 16 - ( 2

0

or

or

or

l 2 S S

less

lc^>0 (2 Q

2(b) MONTMORILLONITE, A FREELY EXPAtJSlOLE 2-1 LAYER MINERAL. THE INTER-LAYER CATIONS ARE FREELY EXCHANGEABLE

F I G 2

3

Marshall (1935); Maegdefrali and Hofmann (1957); Hendricks

(1942); Schramm and Kwak (1984); Keren (1979); Barshad (I960);

and Brown and Miller (1971) etc, who contributed in ascertaining

the physico-chemical behaviour of the clay mineral vis a vis its

structure, Marshall (1935) and Hendricks (1947) showed that

montmorillonite always differs from its theoretical formula

(0H)^SiQA1^02Q.nH20 because of substitution within the lattice

of Al by Mg, Fe, Zn and Cr etc. and Si by Al giving a series

of group minerals. X-ray studies have shown the stacking of

silica-alumina-silica units in the C-direction, layer being conti­

nuous in a- and b- direction with the result that these exert a

weak bond and an excellent cleavage between them, V/ater and other

polar molecules can easily penetrate between the unit layers

causing the lattice to expand in the c- direction. The dimension

of c axis is, therefore, not fixed but varies from 9.6 A to

substantially complete separation of the individual layers in some

cases. The cation exchange capacity of this mineral is high and

varies from 80-120 mecj/lOO g clay,

Illite;

I t has been well established (Grim et a l . , 1937; Bolt

e t a l . J 1963) tha t i l l i t e has very s imilar s t ruc ture to t ha t of

montmorillonite having 2:1 type of basic un i t s t r uc tu r a l arrange­

ment. However, i t has large number of potassium ions between the

4

silica sheets of two successive units that act as a bridge in

holding adjacent layers together so tightly that water can not

penetrate between these layers. The size of the unit cell is 0

10 A . Amorphous substitution is possible within the lattice

resulting in a wide variation in their composition. Because of

illite's close structural similarity to primary mica, it is

considered to be a member of mica group. The cation exchange

capacity of illite varies from 20-40 meq/lOOgclay.

Vermiculite:

This mineral is similar to that of illite in its structure

(Gruner, 1934; Hendricks and Jefferson, 1938) but the layers held

more weakly together by hydrated magnesium (6 water molecules in

octahedral coordination with Mg) rather than tightly bound together

by l{'"ions, Venniculite has more swelling property than illite

but not as much as montmorillonite.

Chlorite;

It is often called 2:2 type clay (Donahue et al. 1977)

because its layer has two silica tetraliedra, an alumina tetrahed­

ron and a magnesium octahedron. It is similar to the unit lattice

of vermiculite except that the hydrated magnesium in vermiculite,

is a firmly bonded magnesium hydroxide octahedral sheet in chlo­

rite. Chlorite do not swell when wetted with water and have low

cation exchange capacity varying from 10-40 meq/lOOg clays.

s

Kaolinite;

Kaolinite is a hydrous aluminium silicate of approximate

composition AlpO,.2Si02.2H2O, The structure of this mineral was

suggested by Pauling (1930) and further work on the structure

rapidly followed by Gruner (1932). Kaolinite, Nacrite, Hallocite

and Dickite are the isomers of kaolin group. Kaolinite is 1:1

type clay having only one sheet of silica tetrahedra per sheet of

3 + alumina octahedra per layer. Almost no substitution of Al for

4+ 2+ 3+ Si or Mg for Al has occurred in kaolinite, so the net

negative charge is zero and thus the cation exchange capacity is

low. However each layer has one plane of oxygens replaced by

hydroxyls which result in strong hydrogen bonding between the

oxygen and hydroxyl layers of ad;jacent units. Because of such

strong hydrogen bonding, kaolinite do not allow water to penetrate

between the layers and have almost no swelling property. The size

of unit cell is 7.2A . The cation exchange capacity of this

mineral varies from 3-15 meq/IOOg clay.

Amorphous clays;

These are the mixture of crystalline and amorphous oxides

and hydroxides of silica, iron, aluminium and other elements which

are also exist in soils (Schwertmann and Fischer, 1973; Bigham

et al.^1978; Koon et al.^1980; Adam and Kassim, 1984; Mehlich,

1962;Basila, I962) in varying proportion. A very little research

G

TABLE - I

C.vl\OJ UXCi NlGE C^PhClTI, SURi- ACE AREA, AND BASIC UNIX AliR^^CiK-

,..:i\xo O/ V..RI0U3 CLAY InlkER/vLS Al^ Al-iORHIOUS MATERIALS.

i-iineral ma t t e r

Phys ica l p r o p e r t i e s

Cat ion Surface exchange a rea capac i t y (3^^ ^^^^^^ (meq/100g) p e r gram)

Bas ic u n i t arrange­ment

K a o l i n i t e

Montfflori l lonite

l l l i t e

Ve rmicu l i t e

C i a o r i t e

3-15

10-Ao

10-40

7-30

80-150 600-800

65-100

100-150 60O-8OO

2 5 - ^

1:1

2:1

2:1

2:V

2:2

a

Oxides and nydrox ides

2-6 100-800

* From Ba i ly and V/hite (1964) .

D i f f e r e n c e witii montmor i l lon i t e :

a ) A l a r c e number of K ions Detween s i l i c a sheet;j of two succe^ive

u n i t s and ajuorphouj s u b s t i t u t i o n i s p o s s i b l e .

b ) S imi l a r t o i l l i t e but has tiie l a y e r s he ld more weakly t o g e t n e r

by hydratod mac,nosium r a t n e r than K i o n s .

7

has been done on these materials regarding their physical and

chemical properties and their contribution to soil characteris­

tics. Hsu and Bates (1963) have reported that these amorphous

clays have positive charge and ijiay contribute significantly to

anion exchange capacity of the soil that depends upon the pH of

the soil solution.

SOIL ORGANIC MATTER

The soil organic matter (SOM) or humus may be defined as

the organic residue left behind after microbial decomposition of

plant and animal remains, frequently dark coloured and possessing

certain characteristics physical and chemical properties

(Waksman, 1936), Its synthesis and degradation constitutes a

dynamic process and depends largely on soil environment. In

general, humus may be divided into two main groups as follows:

1. liunio Substances; Transformed products bearing little or no

resemblance to the anatomical stiMctures from which they are derived,

2. Nonhumic Substances: Unaltered remains of plant and animal

tissues and also organic compounds that have definite character­

istics.

The humic substances can further be subdivided into three

main subgroups (Banerjee, 1979) according t6 their solubility in

alkali and acids, namely:

8

(i) Humic acid; Soluble in alkali and insoluble in acids.

(ii) Fulvic acid; Soluble in both alkali and acids,

(iii) Huciin; Insoluble in both alkali and acids.

Accumulation patterns of humic and fulvic acid fractions have

been studied by various workers (Goh et al, 1976; Schnitzer and

Khan, 1972; Syers et al. 1970; Kilham and Alexander, 1984) to

sliow that the humic acid concentrated principally in the surface

or inimediately below the surface horizon v/hile fulvic acid

fraction extends to much lower depth and is hardly precipitated

from an alkaline extract by acid because of its more functional

groups (Sclinitzer and Khan, 1972; Stevenson and Goh, 1971).

The chemistry of humic substances has extensively been

studied in recent years (Ghosh and Schnitzer, 1980; V/ilson, I98I;

V/ilson and Goh, 1983; Wilson et al,, 1983; Newman and Tate, 1984)

to characterize their composition and properties in soil. The

kind of 30il and its environment and the method of extraction

have been considered (Tan, 1978) as the conflicting factors to

affect the nature and characteristics of t]ie huiaic substances.

The need to standarize the method of extraction is, therefore,

stressed (Flaig et al. 1975; Burgej, I966) as it influence tlio

chemical behaviour of these substances. For example. Tan (1978)

extracted humic substance with UaiP^^Y ^"^ ' ' ^ ^^ study the

changes in IR spectra. It was reported that Na^PpO^ yield HA

with better resolved spectra than NaOH, and allowed to observe

9

the difference in Ha specti'a between soil (groups. The structure

of humic materials extracted from marine environments are highly

aliphatic and, from terristorial environments range highly

aromatic to higlily aliphatic (Wilson & Goh, 1983).

In general, humic acid molecules are composed of an

aroiuatic and aliphatic parts v/iiich are linked together (Zunino

and Martin, 1977), Hurnic acid consists of phenolic and other

aromatic units witii amino acids, peptides, polysacharides etc.

Tue functional ciiemical analysis revealed that the major functional

groups in hvunic acid are carboxylic, phenolic, alcoholic, conju­

gated ketonic, carbonyl, raethoxy, amino (-NHp), secondary amino

(-KH-) and ring nitrogen. All these groups are electron donar,

hence can coordinate metal ion which behave as electron acceptor.

The presence of large concentration of oxygen containing groups

(-COOH, -OH, and -C=0) in humic materials tend to mai e them

hydrophilic. V/hile the aromatic rings, fatty acids, esters and

aliphatic carbons provide them a hydrophobic nature. Thus, the

humic materials are considered to have a simultaneous hydrophilic

as well as hydrophobic nature and hence capable of adsorption of

hydrophouic and hydrophilic substances on its surfaces.

On the basis of numerous analysis made on hunic and fulvic

acids, the main differences between model HA and FA v/ere r('porL.-;d

(Sciinitzer and Ghosh, 1y79) as follows: Total acidity, alcoholic

Oh, and CCOH content of the FA are appreciably higher than liA

10

'.viiile the nuiubcr ol' phenolic <JH, total C- 0 and -OGII-,- t roups

are a .proxiwately same in both the substances. The hii:,her E,/E^

ratio of FA than that of h^ indicates the lower particle size

of FA.

The macromolecular structure of humic and fulvic acids

has been studied by various workers (FiUkherjee and Lahiri, 1958;

Visser, 1964; Flaig and BeutaloSpacher, I968) and the concepts of

•Sphero-colloid' and Flexible linear configuration'put forward.

It v/;is shovm tiiat the hA and FA benave like 'Sphero-colloid' at

high sample concentration, low pH, or in presence of sufficient

neutral salt concentration wnile they are Flexible linear colloid

• in normal conditions (Ghosh and Schnitzer, 1980) that are pre­

vailing in soils. The chemical structure and reactions of hiMic

substances have been a subject of researches of nearly two cen­

turies, yet much remains to understand about these substance.

Considering various aspects of reported literature, Schnitzer and

Ghosh (1979) proposed a model of partial chemical structure of FA

as shown in Fig. 3. The molecular arrangement may account for a

significant position of the fulvic acid structure. Besides the

Vunder IVaals inLeraction and TV-A" bonding, attraction betwen n

Liie building blocks is also likely, mainly tiirough hydrogen bond­

ing which luaicuo Lhe i;LniCture flexible ponnitting building blocks

Lo aggregate and disporso reversibly depending upon the environ­

ment, viz. pK, ionic strength and nature of metal ions present

etc.

U

X u °xP

=o^.

g <

>

3 LL.

o-u u-o ^ ^ ' o o /

1 /

' X / o _ o u=o X V /

-= -<0-s ^ ) — ( X / \ X

o o N

^ ^ '^

\ j O

U-o UJ cc 3 H O 3 a: CO

<

o UJ

_J < 1— a: <

11

Humin is a fraction of aoil huiiius which is strongly bound

to clay minerals after the usual alkali extraction of humic acids

and is known to resist the extraction. Khan (1945) and Zyrin

(19^8) reported that a part of humic substance known as humin,

consists of humic and fulvic acids, but the only difference is

that the humic acid extracted from humin freiction contains lower

percentage of oxygen and hydrogen than that extracted from the

decalcified soil. Besides, the humic and fulvic acid content,

hymatomelanic acid has also been reported to be present in humin

fraction (Benerjee and Mukherjee, 1972).

SOIL WATER

Soil water is an important constituent of soil which helps

to control soil air, soil temperature, evapotranspiration require­

ment and supply of nutrients to growing plants (Brady, 1974),

The soil water content vary with the soil texture and vary from

5.1 to 11.9 percent (Donahue, 1977).

In a study of water retention in soils, Ali and Biswas

(1968) determined the relationship between the nature and amount

of clay in soil and vi ater retention capacity. It was found that

the water retention and release v;ere maximum in bentonite clay

followed by illite and then kaolinite. The amount of available

water in soil was also found to be related with silt (Abrol and

Bhumbla, 1966) and organic matter content (Ali, 1965).

12

Water niovi ment in soils ia an another Important ajipect

of soil water relationship since it decides the amount of water

stored in the root zone, or the depth to which applied v/ater v/ill

move or whether the soil will percolate salt to prevent the deve­

lopment of soil salinity. The movement of water in soil is

influenced by the location, extent, and physical characteristics

of the different horizons.. Since a major portion of water either

from rainfall, or from irrigation moves under unsaturated condi­

tions, it is important to determine the hydraulic conductivity

under unsaturated conditions. The references associated with the

work on the subject are Luxmoore et al. (1977); McNeal (I968);

Lagerwerff (1969); Sojka et al. (1977); Clothier et al. (1977)

and Nakano (1977) etc.

SOIL iilR

The soil air mainly consists of oxygen, carbon dioxide,

nitrogen and nitrous oxide etc. It has been observed that the

composition of soil air varied with the climate conditions

(Russell and Appleyard, 1915) as well as with the nature of the

ijoil (Jonc, 1981).

Using various analytical methods i.e. IR spectroscopy,

Gas chromatO[j,raphy etc., nitro/j,on and nitrous oxide gases have

been measured in soils (Arnold, 1954; Dowdell and Smith, 1974)

which may be a cause of nitrogen losses under an aerobic condi­

tions due to denitrification processes. The other physiologically

13

active gases like ethylene, methane, hydrogen sulphide, volatile

latty acids, alcohols, ketones and aldehydes have been reported

to be ibrmed in water logged soils by microorganisms (Smith,

1977).

MICROBIALS AND THgJR ACTIVITIES IN SOIL

Small living things are biologically classified as

plant (microflora) or animal (microfaiina) and are considered to

be present in the soil surface or in top few inches of the soil

Having their population in billions per gram of soil (Donahue,

1977). It is a universally knov/n truism that these microorganisms

affect and influence the properties of soil.

Soil microfaunae primarily comprises of:

(i) Protozoa

They are primitive, unicellular microscopic animals tiiat

feed mainly on bacteria and hence are believed as a controlling

factor upon tae abundance of bacteria. Thus influence micro­

biological populations and hastens the recycling of plant nutri­

ents. The main protozoan groups are amoebae^ flagellates and

ciliates,

(ii) Nematodes

Nematodes are microscopic, unsegmeixted, thread l i k e woniiS

and may oe c lasni f ied according to t h e i r feeding hab i t s . Omnivo-

14

rous , prcdaceous and p a r a s i t i c nematodes are common in s o i l s .

So i l microi'lorae consis ts of bac te r i a , fungi, ac t ino-

mycetes and algae which occur in almost a l l s o i l samples.

( i ) Bacteria

Bacteria are most abundant groups usually present in soils.

These are unicellular and include spore forming and nonspore-

forming rods, cocci vibro and spirills. They vary considerably

in shape, size and in their energy requirements (aerobic and

anaerobic), energy utilization (autotrophic and hetrotrophic) and

xn relation to plaxits and animals (Saprophytic and parasitic).

Some specific autotrophic soil bacteria can oxidize aimaonia to

nitrites and then to nitrates. Some other bacteria can also

oxidize sulphur, iron, manganese, hydrogen and carbon monoxide.

Another autotrophic bacteria may reduce the nitrates to inert

nitrogen gas. While hetrotrophic bacteria includes both nitrogen

fixing and nonnitrogen fixing kinds, Clastridium (more abundant

in poorly drained acid joils) and Azatobacter (more abundant in

well drained neutral soil) could fix atmospheric nitrogen into

soils.

(ii) Fungi

Fungi caii be classified according to their nutritive process

and are parasitic, apropiiytic or symbiotic. Parasitic fun^i de­

composes resistant cellulose, lignins and gums resulting holes in

15

soil and cause plant diseases. Saprophytic funfii obtain their

energy from decomposition of organic matter while symbiotic fungi

live Oi. the roots of certain plants in a dependent relationship

in v/iiicli both fungus and plant are mutually benefitted,

(iii) Actinomycetes

Actinomycetes are ctiaracterized by branched mycelia

similar to fungi (Nocradia genera), and resembles bacteria when •

the mycelia break into fragments (genera streptomyces and micro-

juonospora), Actinomycetes vary greatly in their biochemical pro­

perties in relation to higher plants and animals and in their

effects on soil bacteria.

(iv) Algae

Soil algae are microscopic, chlorophyll bearing organisms.

Tlie main groups are the green, blue green, yellow green and

diatoms. They develop tha t in moist f e r t i l e s o i l s . Certain blue

green algae have demonstrated the a b i l i t y t o f ix ni trogen from

atmosphere. Tiie species of these type of algae genera are nostoc,

Gcytonema and anabaena (Cameron and i?\iller, I96O; Mayland et ol .^

1966).

(v) Vj ruses

Viruses are noncellular organisms and are composed of

specific nucleic acid surrounded by a coat of protein. They can

multiply and grow only jaside living cells.

I n 0

The microbial activities in soil are largely responsible

for the maintenance of coil fertility as well as soil properties

(Russell, 1973). A nuij.ber of biochemical transformation viz.

amiuonification, nitrification, denitrification, symbiotic and non

symbiotic Np- fixation etc., soilre^iration sulphur, phosphorus

and other trace metal transfonnation have been reported to occur

as a result of microbial activities in soil (Parr, 1974; Gov/da

et al. 1976; Bollag and Henninger, 1976; Vlassak, 1975; Gaur et al.

1977) etc. Microbials mineralize (Reich and Bartha, 1977);

oxidize (Pepper and Miller, 1978) and reduce elements in soils and

indirectly influence their solubilities. Pesticides are consider­

ed to alter the number of activities of microorganism in soils

(V/ainwright, 1978), Atmospheric pollution is also considered by

v'/ainwright (1980) as a factor to effect the microbial activities.

Studies on the nitrogen fixation by root nodule bacteria

and Rliizobium have been a subject of considerable research (Reddy

and Patrick, 1979; Charyulu and Rao, 1979). The nodulating bac­

teria of various legunies are mostly those of the cowpea group

which is very well represented in India and the tropics. The pea

(R, Leguminosarum), and bean (R, Phaseoli) groups are represented

by few legume hosts. Nitrogen fixation by root nodule bacteria

is influenced by many factors, such as, nitrogen status of the

soil, supply of nutrient elements like phosphorus and molybdenum

etc.

17

ORGA?:iG COMPOUNDS IN SOIL

A number of organic cheiaicals are reported to exist in

soils, 'The transformation of organic compounds occurs mostly

throu^u biochemical processes caused by the action of micro­

organisms, particularly of their enzyme systems. The organic

compounds which are generally found in soils are:

(a) Aliphatic acids

A large number of organic acids are intermediates of

metabolism of plants and microorganisms or can be derived from

them. Some are products of oxidative degradation of organic subs­

tances (Yoshida and Nakadate, 1964). The amounts of formic and

acetic acid depend upon the soil conditions in which they exist.

The level of formic acid and acetic acid ranges from 0.5 to 0,9

and 0.7 to 1.0/g of soil respectively.

Many Organic acids occur in the aqueous systems of both higher

and lower fonns of plant life. Aliphatic acids of conmion occurrence

in plants include the lower members of the fatty acid series:

formic, acetic, propionic, butyric. Of equa].ly wide distribution

are the following acids: oxalic, glycolic, lactic, tartaric.

Other acids are citric, succinic, malic acids are found

in many fruits and leaves. In poorly drained soils the conditions

for the formation of aliphatic acids by microorganisms are more

favourable than in aerobic soils. For instance Takijima (19^1)

has reported the accumulation of acid in soils are in the order

18

a c e t i o b u t y r i c >t'ormic >fumaric, propionic, va l e r i c , succinic

and l a c t i c acids in .somo cases.

Some work has been reported on the influence of acids on

LLa crovrth of p lan ts and concluded both favourable and unfavour­

able e f fec ts . Organic acids are also involved in the so lub i l i za ­

t i o n , and t ranspor t of the mineral pa r t of t-he s o i l s , Schwartz

e t a l , (1954) have been f i r s t to use modem chromatographic tech­

niques for character izing a l ipha t i c organic acids in aerobic

s o i l s ,

(b) Amino acids and Proteins

About 20 to 50 percent of the organic bound nitrogen is in

the form of amino acids in soils (Bremner, 1965). The total amount

does not exceed 2 pg per g soil. The composition of the amino

acids from decomposing plant material, microbial synthesis or

exudation by roots, seems to have no such influence on the compo­

sition of proteins in soil (Stevenson, 1956). But characteristic

differences occur when organic substances are decomposed by selec­

tive groups of organisms (Cheshire et al,^1965). In soil hydro-

lysates, leucine and iscleucine, lysine,, alanine, glycine, valine

and sulphur corrtaining amino acids are found mostly in larger

quantities than the other aniino acids.

(c) Carbohydrates

The dead Vcocfc^tive mat^jrial contr ibutes the major par t of

carboiiydrates to so i l organic matter in the form of di f ferent

19

polyiiier saccharides, especially cellulose and horaicellulose.

The microorgc^nisms synthesize polysaccharides and other carbo­

hydrates and furthemiore they also decoiLpose the polysaccharides

from plant material. The approximate content of carbohydrates in

soil organic matter is 5 to 16 percent isolated by various pro­

cedure (Cheshire and hundie, 1965; Donnaar, 1967; Gupta and

Sov/den, 1963).

Gupta (1967) listed some of the different carbohydrates

v/.iich have been found in soils as;

(i) Monosaccharides

Hexoses : glucose, glactose, mannose, fructose.

Pentoses: arabinose, xylose, ribose, fucose, rhamnose,

(ii) Disaccharides

Sucrose, cellubiose, gentiobiose,

(iii) OliKosaccha'rides

Cellotriose.

(iv) Polysaccharides

Cellulose, hemicellulose.

(v) Amino sugars

Glucosamine, glactosaiaine, n-acetyl - D glucosamine.

20

(v i ) Sugar alcohols

Manitol, inosi tol*

( v i i ) Sugar acids

Glacturonic, Glucoronic acid,

(viii) hethylated sugars

2,0-methyl-D-xylose, 2,0-methyl-D-arbinose, 2,0-

methylrhamnose, 4,0-methyl glactose,

(d) I^ionocyclic phenolic compounds

Phenolic compounds in soils can be derived from phenolic

plant constituents such as flavones, flavanols, catechines,

phenolcarbonic acids and others formed by microbial synthesis.

(e) Organic phosphates

Soi l organic matter contains a small port ion of organic

phospnates. The cons t i tu t ion of the compounds iden t i f i ed so far

allows the assumption tha t they are derived from nucleic acids ,

i n o s i t o l phosphates and the phospholipids. Some of them come

in to the so i l by plant mater ia l , otiiers are synthesized by

microbes.

21

PESTICIDES

Pesticides are chemicals used for controlling the pests

like fungi, insects, herbs or other animal pests that attack crop resources

food ii other useful to man. The general definition for pesti-

cides was given by Ware (1978) as "Any substcince used for con­

trolling, preventing, destroying, repelling or mitigating pests

is known as pesticide ",

Pesticides can broadly be classified into various classes

according to their use such as herbicides, fungicides and insec­

ticides. There are also rodenticides, nematocides, molluscacides,

acaricides, and weedicides etc.

Herbicides

Herbicides are those chemicals which are used to destroy

or supress the growth of unwanted herbiceous and weed plant with­

out injuring others. Organic chemicals which exhibit herbicidal

and plant grov;th regulator properties are numerous and varied

from biological, physical and chemical standpoints. They can be

subclassified into following groups:

(i) S-Triazines; These herbicides conform to the general

formula;

R;

N

N

22

'R.

wht re R and R^ refers to the N-substituted with lower alkyls

and X to CI, OCH^, and SCH, etc. for extensively used S-triazine.

oome of the commonly used S-triazine herbicides are: Simazine,

Atrazino, Atratone, Prometone, Ainetryne. Frometryne etc,

(ii) Substituted ureas; The substituted ui-ea class of herbi­

cides contain a number of widely used compounds such as fenuron,

diuron, monuron, linuron, norea, chloroxuron, fluometuron and

S-iduron etc. Various new herbicides of this group are being eva­

luated. These are used at high concentration rates as soil steri-

lants and at low rates as selective pre- and post- emergence her­

bicides in crop production.

(iii) Phenoxyalkanoic acid; The members of this class of her­

bicides are used primarily as foliar applied treatments. Some

of the important phenoxy alkanoic acid herbicides are;

2,4,5-T; I'iCP; LCPA; Dichloroprop and Silvex etc. They are gene­

rally empolyed as pre- emergence treatment in conjuQction with

other herbicides because of their sliort residual life.

23

(iv) Carbanilates: Many types of carbanilates snow herbicidal

actions. Some of the most extensively used compounds of this

^roup includes swep, propham, chloropropham and bahban etc,

Sv/ep, propham and chloropropham are used as pre- anergence her­

bicides, while banban is used as post- emergence control of wild

oat in cereals. These compounds are readily degradable by micro­

organisms. They are lost through volatilization if they are

applied to wet soil,

(v) Chlorinated Aliphatic acids; Various chlorinated aliphatic

acids such as 2,2-dichloropropionic acid (dalapan); trichloroace­

tic acid (TCA) and 2,2-dicl:aoroisobutyric acid (FV/-450) etc, have

been used as herbicides,

(vi) /ynitrole; It is a substituted triazole (3-amino-1,2,4-

triazole) herbicide which is used primarily due to its resisti­

vity towards microorganism (Ashton, I96I), However, it was later

obuorved that ciiemical as well as microbial degradation both may

be experienced by this compound.

Besides tiie above most extensively used herbicides, there

are many otiier compounds which are also used as herbicides. They

include: Pyridine, N-aliphatic carbamates, Dipyridyls and many

others.

Fungicides

Fungicidoc are those chemicals which are used to control

24

various fungi and fungus bom diseases like mil.dew, blights,

smuts, rusts, scab, spot, rot etc. Fungi are pathogaiic organisms

which may be present on foliage surface as powdery mildews, they

may remify through plant tissues.

Fungicides are of two main types;

(i) Surface fungicides: These fungicides are used to apply to

foliage as sprays or dusts. They do not enter the plant tissues

but kill the fungus and the surface spores. They include:

Bordeaux mixture, lime sulphur, preparations containing Cu, Zn,

Mg, As, S and other natural plant extractions.

The organic surface fungicides are: orgejiic mercury, alkyl

mercury and phenyl mercury. They are appeared to cause wide

spread environmental hazards due to much toxic mercury metal

(Dix, 1981), The organic thiocarbamates such as thiram, ziram,

zineb and Maneb etc. and phenolic compounds such as dinitrophenol,

dlnocap and many others have been used as organic surjPace fungi­

cides to replace organic mercury ccmpounds.

(ii) Systemic fungicides: These fungicides are absorbed into the

plant through leaves, roots and seeds and are translocated within

the plant tissues. Consequently this group is more effective than

the surface fungicides. However, newer systemic fungicides are

continuing to be developed, benomyl, MBC, TBZ, thiophanates, dowco,

triarimol, and carboxiin etc, are in common use. All organic fungi-

cides have low toxicity to plants, birds and mammals, so they are

25

not potentially hazardous in the short term. Some products contain­

ing metal that are known to accumulate in food chains, may pose

some health hazards.

Insecticides

Insecticides are those chemicals which are used to kill or

control various insects. They can be applied directly to soil or

as sprays or dusts to foliage plants. Pests such as wire-worms,

chafer grubs and root maggots in soil are extremely difficult to

be controlled due to their relatively inactive nature. Volatile

insecticides are more beneficial as they can permeate the soil

crevices and reach the inactive stages of the pests such as eggs

or pupae. In general, insecticidal chemicals may be classified in­

to follov/ing groups:

(i) 0rganochlorines; Among various organochlorine insecticides,

the most important and best known is DDT, it was followed by BHC

(1942), Within a very short period, a range of these insecticides

were developed as chlordane (19^5), heptachlor (1945), toxaphene

(1947), methoxychlor (1948), aldrin (19^8), dieldrin (19^8),

endrin (1951), and endosulfan (1956) etc. and are used as insecti­

cides. In general, these are wide spectrum insecticides used to

kill a great variety of pests.

(ii) Or^anophosphorus: The organophosphorus insecticides

includes: Parathion (1944), diazinon (1952), trichlorophon (1952),

26

phorate (1954), carbophenothion (1955), disulfoton (1956),

dimethoate (1956), fenthion (1957), thionaz:Ln (1959), menazone

(1961), difXonatG (I966), chlorfen vinphos (1963) and others like

malathion, phosphamidon, dichlorvos etc, Tlie organophosphates

are much more soluble in v/ater, but their volatility is nearly-

equal to that of organochlorines. These insecticides are less

persistent in comparison to organochlorines.

(iii) Carbamates; Some carbamate compounds have also been used

as insecticides. They include CHyiC, carbofuron, bendiocarb,

aminocarb, metabal etc. Most of the carbamates act on insects in

a similar way to the organophosphorus compounds. They persist much

less than organochlorines but longer than organophosphorus compounds

With increasing use of pesticide in agriculture, these

chemicals are harmful for environment, Rachael Carson (1965) was

one of the first, v/ho recognize the dangers of pesticide pollution.

She produced evidence of toxic effects upon wild life and potential

hazard to man. Since then, a number of workers have carried out

experiments on various aspects of environmental pollution caused

by pesticides (Heuper and Conway, 1964; Mellanby, 1972a,b).

Some pesticides are described as stable and persistent in

soil for varying period of time, Watter and Grussendorf (I969)

showed that organo-chlorine insecticide deposits on the walls of

stores might be a source of residue in grains. Few organochlorine

and organocarbamate insecticides are feebly systemic and are

27

adsorbed by roots or leaves, metabolized, and translocated in

noninsecticidal amounts to leave persistent and undesirable

residues at harvest. Duggan (1968) showed that oil containing

seeds may concentrate these to one tenth of the original content

in soil,

Menzie (I969) has classified the possible biotransfomia-

tion of pesticides in plants and soils. These include; oxidation,

dehydration, dehydrohalogenation, reduction, conjugation, hydro-

lytic reaction, exchange reaction and isomerization. The factors

including the presence of residues may be artificial or natural.

The natural factors are-more sobtle in their effect on residues

in plants. They include the plants (Stoller, 1970); soil

(Harris and Sans, 1969); Weather (Li-nkson et al, 1965); penetra­

tion (Frank, 1967; Frank, 1970); absorption (Hulpke, 1970);

translocation (Nash and Beall, 1970) and diffusion. Animals and

humans absorb these chemicals from their food,and accumulate them

in specific body organs until it reaches a lethal threshold dosage

for species. In general, the harmful effects of pesticides can

directly be related to their persistence and accumulation in the

environment, as well as within the body tissues of animals and

humans.

Various aspects of pesticide residues have been studied

by many workers. Some of those include; persistence (Robinson,

1970); pesticide in peoples (Waasherman et al,, I967); transloca­

tion (Helling, 1971; Wain and Carter, 1967); residues in feed,

food and fibre plants, and tobacco (Finlayson and MacCarty, 1965).

28

TRACE METALS

Sixteen elements are knovm to be essential for plant

growth and microbial activities in soils. Of these some are

needed by plants in larger amounts and are called major nutri­

ents v/hilc others that are required in smaller amounts are known

as micro or trace elements. These are iron, manganese, zinc,

copper, boron, chlorine and molybdenum, A part from these, some

other elements such as Pb, Cd, Cr, Ni, Ag, Hg, As, Se, V and Ba

etc. are also knovm to be present in soil in trace quantities,

however-, they are not essential for plant or animal growth and

found to be toxic to men and animals and produce undesirable

effects (Singh and Singh, 1977; Dijkshoorin et al,j1979;

Lauwerys et al.^1979j Schmitt, et al,_,1979 etc.). Forbes et al,

(197' ) have reported that the adsorption of heavy metal cations

on solid solution interface, is not simply an electrostatic but

consider (i) as a function of properties of the solid surface

and the adsorbing species, (ii) the ability of the adsorbing metal

ions to hydrolyse in solution in determining their affinities for

the surface of soil minerals.

In recent years, man has utilized the sewage and indus­

trial v astes as a source of micronutrients in most of the deve­

loping countries like India, Large population centres producing

tremendous amount of sev/age sludge and rapid ::Lndustrialization

29

incorporating many heavy metals, however, aroused the concern

over tiieir possible use in agriculture. Composition of different

sludge and industrial wastes has been studied by various worKers

(Stover et al.^1976; Anderson and Nilson, 1972), It was found

that heavy metals constitute a major part of its composition, Thej

are accumulated in soils because of their excessive use and causes

a hazardous problem to plant and animal life.

In most of the studies, it has been shown that the metals

added to soil remain in the upper few inches (Williams et al,_,

1980; Page and Chang, 1975) because of various immobilizing i|;iecha-

nisms like precipitation of specific adsorption on oxides, clay

minerals and organic matter. Considering the sludge as a complex

mixture of organic and inorganic species, various forms of trace

metals in soil could be understood (Gregson and Alloway, 1984;

Tills and Alloway, 1983).

The chemical behaviour of trace metals has extensively

been studied in relation to soils and clays (Bowman et al,j1981;

Hodgson, 1963; Tiller et al,^1979). It has been observed that

Pb may form soluble inorganic complexes with Einionic groups like

hydroxyl, chloride, sulphide, phosphate and carbonate according

to soil pH, and acidity of interacting ions, Richard and Nriagu

(1978) observed that Pb remains as carbonate species, particularly, 2

Pb(C0,)2" ^'^ P^ ^" between 6 and 8, while at pH-<6 and in absence 2+ +

of carbonate, Pb , PbCl , and PbClp v/ere predominant inorganic

30

spec ies . Santillan-Medrano and JurinaK(1975) reported the for ­

mation of PbCO , Pb(0H)2, ^^3(^0^)2, Pb^(PO^),OH, and/or

Pb,0(1^^)2 species at pH in between 7.5 and 8,0 , Pb has also

been observed to complex with sulphur based amino acid, cystein

and fulvic acid (S i l l en and k a r t e l l , 1964; Schnitzer and Skinner,

1967). Gregson and Alloway (1984) studying the Pb speciat ion in

heavi ly pol luted s o i l , reported tha t Pb occurs as both high and

low molecular v/eight organo-Pb-complex depending upon the i n i t i a l

pH. In a potentiometric study of metal-HA complexes, Stevenson

(1977) reported tha t there are two or more binding s i t e s in Pb-HA

complex formation. Thus, 2:1 and 1:1 Pb-HA complex are formed to

give a chain l i ke s t ruc ture by displacing H ions from exchange

s i t e s or by releasing proton from hydration water of metal ion.

In comparison to other heavy metals , the order of s t a b i l i t y cons­

t a n t for metal - HA complex i s as follows:

C u > Pb§> C d > Z n

Bittel and Miller (1974) studied the adsorption behaviour of Pb

on luontmorillonite, kaolinite and illite to show that the adsorp­

tion sites were all alike and there was little or no interaction

between adsorbed ions. On geothite, Pb was reported to be speci­

fically adsorbed and its distribution between solid and liquid

phase is pH dependent (Forbes et al., 197V). It was reported

(Forbes et al., 1976) that for each Pb ion adsorption, nearly tv/o

moles of H ions are displaced from interface which was in the

31

direct contrast of the mass action approach of Grimme (1968). 2 +

Again, the Pb has hydrolysable nature, its adsorption could be

considered to occur via the adsorption of PbOH and Pb(OH)p

species at higher pli values (James and Healy, 1972).

Cadmium is accumulated in soils , mainly through continuous

application of sewage sludge; (Anderson and Nilsson, 197^) on the

soil colloids is a major factor influencing the distribution of Cd

between aqueous and solid phase in soil water system. Lagerwerff

and Brewer (1972) investigated the exchange behaviour of cadmium

with Al and Ca treated soils. It was found that cadmium adsorp­

tion decreased with increasing AlCl^ or CaClp and decreasing NaCl

concentration in soil solution. The effect of exchangeable cations

on the Cd sorption by montmorillonite was studied by Garcia-Mira-

gaya and Page (1977) who observed the following decreasing order:

Na->K - > Ca -•> Al-mon-tmorillonite.

Jarvis and Jones (1980) found that the cadmium strongly sorbed

by soils when added in the amount comparable to that added through

sewage sludge or phosphatic fertilizers. They also observed that

various cations are capable of disorbing Cd from soil in the order:

Pb > Zn > Cu > Mn > Ca

Nickel is another phytotoxic (Foronghi et al., 1976; Ormrod, 1977)

and zootoxic element , especially to marine life (NRC, 1975; Toth,

32

1968). It causes carcinogenesis (NRC, 1975). Nickel is generally-

accumulated in soils through industrial and municipal wastes.

It is introduced into human and animal food

chain mainly through water and food plants via soils. Thus, the

availability of Ni in soil solution and its absorption by plants

is an important process which is governed by its chemistry in

soils, Sadiq and Enfield (198A) studied the solid phase formation

and chemistiy of Ni in soils. It was observed that nickel behaves

in several ways depending upon the pH of soil solution. In Fe

dominated soils, nickel ferrite (NiFe^O,) and Ni(PO.)2 are preci­

pitated depending upon the availability of Fe in soils. Nickel

oxides and hydroxides have been identified in soils having pH

greater than 9. Other species which are reported to precipitate

are carbonate, sulphate, phosphate, chloride, hydroxy complexes

like NiCOH)"*", Ni "*", NiSO^ , NiHPO° etc. Bromo-, chloro-, iodo-

and nitrocomplexes etc.

In general, it has been pointed out that atmospheric fall

out from ore smelter contributes significantly to soil contamina­

tion with heavy metals (Goodman and Roberts, 1972; Cartwright et

al., 1977; Franzin et al., 1979). They exist in soil as bound

species with carbonate, oxide, organic matter and as exchangeable

or incorporated in crystal lattice (McLaren and Crawford, 1973;

Gibbs, 1977). Mattigod and Sposito (1977) reported the sulphate

complex species of these trace metals at low pH values, which dec­

reased with increasing pH due to their complexation with organic

matter.

33

Glnzburg (I96O) reported that the preferential uptake

of metal cations followed the order Pb > Cu > C a > B a > Mg >• Hg

on montmorillonite and that the capacity of the heavy pietals

to replace the Ca on Kaolinite is in the order Pb > Cu >Hg.

ADSORFTION

The term adsorption was first used by Kayser (1881) at

the suggestion of E-du Boise-Raymond and refers strictly to the

existence of higher concentration of any par-ticular component at

the surface of liquid or solid phase than is present in the bulk.

In general, adsorption may be classified into two types

namely physical and chemical. The physical adsorption occurs

mainly due to weak forces, like ion-dipole, dipole-dipole, polari­

zation or induced dipole, and Vander Waal's forces etc. It

involves usually lesser heat changes of the order of 0.5 to 2 KCal

or less (Adams, 1973; Glasstone, I960). This phenomenon is more or

less non-specific, reversible and temporary in character. While

chemical adsorption is due to the formation of chemical bond

between the adsorbent and adsorbate molecules. It is characteri­

zed by a large heat change as 5-20 KCal, In some cases, the value

of the heat of adsorption has been reported to be in the range of

15 to 50 KCal per mole. (Adamson, I96O; Biggar and Cheung, 1973;

Gregg and Singh, 1967). Thus, the chemical adsorption is a speci-

34

fie, non-reversible and permanent surface phenomenon.

Adsorption of inorganic and organic components have gained

considerable importance in the field of soil chemistry. In

recent years, Khan and Bansal (1980); Joshi (1986); Goodman (1986);

Cline and Oconnor (1984); o'Connor et al. (1983); Kuo and Baker

(1980); Ellioott and Huang (1979); Curtin et al, (1980); Reddy

et al. (1987); Rick et al, (1987); and others have studied the

adsorption phenomena in relation to soil and clays in various

aspects.

The clay minerals as well as crystalline and amorphous

obcide.s and hydroxides both having a capacity for adsorption due to

coulombic, and/or physical forces. Organic pesticides adsorb on

both organic and inorganic surfaces depending upon the chemical

properties of adsorbent and adsorbate (Weber, 1972), The organic

matter has been reported to have a highest cation exchange capa­

city (200 to 400 meq/100 g) and surface area (500 to 800 sq. m.

per gram) which are comparable to montmorillonite and vermiculite

(Bailey and White, 1964), Basic pesticides were reported to be

adsorbed strongly on soil organic matter (Weber et al,,1969) and

expanding lattice clay minerals (Weber, I966; Weber, 1970), Acidic

pesticides were adsorbed in moderate amounts on organic matter

and relatively low amounts on clay minerals and hydrous metallic

oxides (Carringer & Weber, 1974; Scott & Weber, 1966; Weber, 1972).

While non-ionic pesticides were considered to adsorb in greatest

amount by organic matter but their adsorption by clay mineral was

35

also important for organophosphate and several other pesticide

families (Weber, 1972), In addition, it has been reported that

carbamate and organophosphate insecticides were adsorbed by soil

organic matter (Leenheer and Ahlrichs, 1971). The physico-

chemical nature of adsorbate which controls the role of the mole­

cules may be summarized as follows: (i) Chemical character, shape

and configuration, (ii) Acidity or basicity of the molecule, (iii)

Vater solubility, (iv) Charge distribution on the organic cations,

(v) Polarity, (vi) Molecular size and (vii) Polarizability.

Adsorption of inorganic cations with soils has extensively

studied by a number of workers as Curtin (1980); Kuo and Baker

(1980); Graffin and Au (1977) etc. and generally found in the

following order.

. + H''>Al^"*">Ba^-'>Sr^*>Ca^-'>Mg^"*">K'">Na''>Li

The property of adsorption plays an important role in

holding water and plant nutrients and keeps them available for the

use of growing plants. Fertilizers in the form of soluble subs­

tances, are retained on the surface of the soil colloid due to

their adsorption and indurate for leaching.

Adsorption equations

An adsorption isotherm represents the functional relation­

ship between adsorbed phase concentration (X/m) and solution con­

centration (Ce) at constant temperature. Generally, two types of

3 r» 0

isotherm equation namely Freundlich and Langmuir equations, have

most frequently been used to describe the adsorption behaviour of

various species in soils,

(a) Freundlich equation; In Freundlich type of adsorption iso­

therm, the concentration of solute species in adsorbed phase is

given by the equation:

Vn x/m = KCe

or ln ( x/m) = InK + ^^n inCf

where, "x/m is the amount of solute adsorbed (X) per mass of

adsorbent ("m ), the constants K and 1/n represents the adsorption

capacity and intensity, respectively, Ce is the equilibrium concen­

tration of solute in solution.

If In (x/m) is plotted against InCe , a straight line is

obtained whose intercept and slope represents the constant K and

1/n respectively. Using the value of K as a measure of adsorption,

the adsorption capacity of various adsorbent may be compared while

1/n measure the non-linearity of the process. If 1/n is unity, the

process is said to be linear.

(b) Langmuir equation; The Langmuir equation may be written as:

./ ABCe X/m = 1 + BCe

37

where, A = adsorption maxima (^g/g ) ; B = coefficient that

reflects the relative rates of adsorption and desorption at

equilibrium and, thus, an affinity term (ml//ag); x/m and Ce are

the same as in Freundlich equation.

The linear transformation of the above equation can be

written as:

C e A . Ce ^ ^ / /^ A BA

The slope and intercept of the plot (Ce/x/m "vs. Ce)

gives the value of constants, 1/A and 1/BA respectively. The

adsorption capacity of adsorbent (A), depends upon the specific

surface area, surface charge characteristic etc. The constant

B is a measure of the adsorption energy.

Classification of Adsorption isotherm

Giles et al. (196O) studied the adsorption from aqueous

solution of a variety of solutes and developed a classification of

adsorption isotherms into S,L,H & C tj^es depending upon the ini­

tial slope.

S -Type;

The S-type isotherms are common when solid had a high

affinity for the solvent. This type of isotherm indicates a ten­

dency for large adsorbed molecules to associate rather than to

38

remain as isolated units. In the S-type curve the slope initia­

lly increased witii increase in concentration due to cooperative

adsorption. At the saturation point where no site remained

vacant slope fill. Such type of isotherms occurred when the ac­

tivation energy for desorption of solute was concentration depen­

dent and or was markedly reduced by large negative contribution

of the solvent,

L-Type;

TiiG L-type of isotherm was formed when the sol id had

a liigh af f in i ty for the so lu te , or the adsorbed solute molecule

were not ve r t i ca l l y oriented. This curve showed tha t as more

s i t e s in the substrate were f i l l e d up i t became increasingly

d i f f i c u l t for a bombarding solute molecule to find a vacant

s i t e . In L-type curve, the solid possessed fev/ s i t e s which were

-/ideiy separated and had large hydrophobic region. This type

of isotherms was reported by Weber (1966) and Bailey et a l ,

(1^j6n) in studying the adsorption of t r i a z i n e pes t i c ides .

H -Type;

Tlie li-type curve was rare and obtained when the solute

has a very high affinity for substrate or there was no measurable

amount of solute left in the solution. The initial part of H-

type isotherm was vertical. This type of curve along v/ith a

platean was obtained in case of chemisorption of fatty acids,

39

(Smith and Puzek, 19^), nanatocides such as telOMe(Singhal and

Kumar, 1976) and ionic micilles or polymeric molecules. The

length o£ plateau indicated the difficulty of formation of second

leiyer.

g-Type;

The C-type isotherm, was obtained when new sites became

available as the solute molecules were adsorbed from the solution.

It represented penetration of substrate micropores by solute with

or without solvent. The small solute molecules were found to be

accompanied by water while the larger were with or without water.

Such type of isotherms were found by Greenland et al, (1962) and

Singhal et al, (1976) in case of amino acid and necaatocide adsorp­

tion respectively,

MOBILITY OF PESTICIDES AND TRACE MSTALS IN SOILS

The movement of chemical substance in soil may influence

ootli its effectiveneas and potential as a contaminant in adjacent

soil, V)fater or air. The substance moves predominantly in vertical

direction in the zone of aeration above the water label (Jordan

et al, 1970), The chemical substance in soil may translocate due

to two general processes namely, mass transfer and diffusion. Any

movement to a considerable distance is said to be occurred by mass

transfer i,e, flow or convection. It is caused by water percolat-

40

ing downward or absorption upward through soil pores. Further­

more, the soils have pores of various sizes, therefore, the

mobility of a particular substance in soils varies with the

particle size. The movement through diffusion may be described

by Pick's law which is;

j _ D ^ and > ^ = D ( - ^ 2 )

It shows that the rate of movement (J) of a chemical substance over

a distance of X at time t is directly proportional to its diffusion

coefficient, D and concentration, C, The diffusion coefficient, D

determines whether the chemical diffuse through air or water.

According to Goring (1967), the chemicals with water/air ratios 4

under 1x10 diffuse primarily through air while those with their

ratios higher than this diffuse through water. It is also obser­

ved that most of the pesticidal chemicals have their water/air

4 ratio more than 3x10 and hence, their movement in soil occurs in

aqueous solutions (Helling, 1970).

Interaction with the soil itself is a highly significant

factor v/hich retards the movement of chemicals in soil. Various

other factors which affects the mobility have been reported by

Builey and V/hite (I96A) and others (Rhodes et al,, 1970; Schreiber

et al., 1971). Some important parameters influencing the move­

ment of chemical substances includes their adsorption, formulation

and their solubility in water, flov; rate, amount of v/etting events,

41

r- e of their application and degradation etc. Some other

iactors like nature of chemical substance and soil colloids,

soil pH, exchangeable cations and anions etc, have also been

reported (Singhal and Bansal, 1978; Khan and Khan, 1986;

G-rover, 1973; Singiial et al,, 1977) etc. to affect the trar^oca-

tion process in soil.

To evaluate the movement of chemical substance in soil,

various methods have been used. In which column chromatographic

iiietiiods and soil tiiin layer are considered as powerfull tools.

Yariouo conventional columns have been used by various workers e.g.

aluminium'rings (Harris, 1957), sectioned monel metal pipes

(Upchurch and Pierce, 1957), stove pipe sections (Rodgers, 1968),

staked time cans (Sheets, 1958), perforated teflon (Kay and Elrick,

1967), rectangular plastic paper (Horowitz, I968) etc. The chemi­

cal substance is analysed in various sections of the column.

Direct analysis of column effluent (Davidson and Santelmann, I968;

Rodgers, 1968) has been carried out for highly mobile substances.

Soil Tnin Layer Chromatography; Thin layer chromatography is an

inexpensive,sensitive, selective and rapid tool of analytical

chemistry used for the separation and identification of inorgaiiic

and organic compounds (Ludwick et al., 1977; Pribyl et al., 1977;

Krahneet al., 1977). Soil thin layer chromatography is an adsorp­

tion chromatography using a thin layer of soil as adsorbent or

stationary phase. While the mobile phase being liquid (generally

42

water) percolate throu iti the stationary phase. This technique

was i'irst successi'uliy used by Helling and Turner (1968). It is

aualo ;oua to conveniioual Tl£ v/ith substitution oi" soil as the

adsorbent phase. Later, this technique was successfully applied

to study the movement oi" various pesticides (Rhodes et al. , 1970;

Helling, 1971a,b,c,- Abdel-Kader et al., 1984; Dedek et al., 1985);

or -anics (Singhal and Bansal, 1978; Krishnamurthy, 1983; Shannon

et al., 1985); and tracemetals (Singhal et al., 1977; Singh et al.,

1985).

The preparation of soil TLC plates is carried out by

spreading a uniionn thin layer of aqueous soil slurry with the

help of an applicator. It is then allowed to stand overnight for horizontal , .

drying in , position (Bremner et al., 1961). The thick-

nesG of tiie layer on soil TLC plates in the range of 0.15 to 2.0 mm,

is unimportant with respect to R . for diagnostic or qualitative

work (Helling, 1971).

The amount of substance applied, depends upon tiie layer

thickness and the v isua l iza t ion method which are inversely pro­

por t iona l to each other . The substance to be studied i s normally

applied by touching the t i p of a f i l l e d cap i l l a ry , micropipette

or microburette to the adsorbent layer . The sample i s placed or

spotted about j> cm above the bottom end of the p l a t e so tha t the

solvent level wi l l be at l eas t one cent'^imeter below the centre

o i' the spot. The diameter of the spot should not exceed 0.5 cm and

should be as small as poss ib le . These p la te s were then developed

43

in developing solution (usually water), air dried, and the spot

is detected by various methods like chanicai reagents, fluore­

scence and iodine vapours etc., but the substance with which the

ccMnponent reacts chemically must not be used. The mobility is then

estimated as R^-values which is the ratio of the distance travelled

by the substance under study to the distance travelled by the

solvent (Helling, 1971). The substance detection on the developed

plate is an important step of this technique and must be made very

clear as it characterizes the adsorption behaviour of that substance

and adsorption capacity of the soil. It was observed (Helling, 1970)

that highly mobile compound without any significant tailing, is

adsorbed linearly on to the soil surface. While in the case of

compounds with lesser mobility exhibiting tailing, shown a non­

linear adsorption. Thus, soil thin layer chromatography provides a

very large field of application for investigating problems in various

applied or non-applied fields.

THE PROBLEM

The application of pesticides, sewage and industrial waste

to soil are finding a great importance in modem agricultural

practices. Their presence in soils may influence the growth of

plants and soil microorganisms. They are also posing some undesir­

able effects on our flora and found due to the indiscriminate use

of pesticides and heavy metals. In India, various food plants have

44

been studied to analyse the presence of pesticides and heavy

metals such as Pb, Cd, Ni, Hg, Ag and many otherso It has been

observed that their concentration exceeds the maximuia permissible

limit in food plants.

Pesticide residues in soil may originate from accidental

or incidental contamination, as from spoilage, from pesticides

in adhering particles of treated soil, by volatilization of pesti­

cides from treated soil or from dusts or sprays drifted by wind,

^hile sewage sludge and industrial wastes and many other processes

like atmospheric fallout, auto ejdiaust, fertilizer impurities,

have produced tlje heavy metal contamination of soils and plants.

Due to the great importance attached with the heavy metals

and pesticides, it was considered worthwhile to undertake investi­

gations along the follov/ing lines which constitute the subject

matter of this thesis entitled, "Adsorption and mobility of pesti­

cides and trace metals with soils and clays".

1. Studies on the mobility of some heavy metals through soil by thin layer chromatography as influenced by organic acids and bases.

2. Studies on the mobility of some pesticides as affected by their chemical characteristics and some soil properties.

^. Adsorption of Cu "*", Pb " and Zn "*" with Ca- saturated illite.

4. Studies on the adsorption of methyl, 2-benzimidazole carbamate (MBC) with clays as affected by various soil parameters.

45

REFERENCES

ABDEL- KADER, M.H.K., STILES, D.A. and RAGAB, M. TH.; I n t . J . Environ. Anal. Chem., 18(4), 281 (1984).

ADAMS, R.S. J r . i Residue Rev., 47, 1 (1973).

ADAMSON, A.W.; Physical Chemistry of Surfaces, In te rsc ience Publ ishers , N.Y. Chap. IV (I96O).

ALL, M.H,; Soil suction moisture re la t ionsh ips in r e l a t i o n t o organic carbon, cat ion and mineralogy of s o i l s , Ph.D. Thesis , P.G. School, lARI, New Delhi, India (I965).

ALI, M.H., and BISWAS, T.D,; Prss. 55th Indian Sci . Congr., 3 , 633 (1968).

ANDERSSON, A. and NILSSON, K.O,; Ambio, 1, 176 (1972).

ARNOLD, P.W.; J . Soi l S c i . , 5, 116 (1954).

BAILEY, G.W. and WHITE, J . L . ; J . Agric. Food Chem., 12, 324 (1964).

BAILEY, G.W., WHITE, J .L . and ROTHBER, G.T.; Soi l Sci , Soc. Am. P r o c , 32, 222 (1968).

BANERJEE, S.K., J . Indian Chem. Chem. S o c , 56, 1094 (1979).

BANERJEE, S.K. and MUKHERJEE, S.K.; J . Indian Soc. Soil S c i . , 20, 305 (1972).

BARSHAD, I . J Tran. 7th I n t . Congr. Soi l Sc i . Madison, 2 , 435 ( i960) .

BASILA, M.R.; J . Phys. Chem., 66, 2223 (1962).

BIGGAR, J.W. and CHEUNG, M.W.; Soi l Sc i . Soc. Am. Proc . , 37, 863 (1973).

BIGHAM, J.M., GOLDEN, D.C., BOWEN, L.H., BUOL, S.W. and WEED, S.B.j Soi l Sci . Soc. Am. J . , 42, 8I6 (1978).

4 r» 0

BITTEL, J .E . and MILLER, R . J . ; J . Environ. Qual . , 3 , 250 (1974).

BOLLAG, J.M. and HENNINGER, N.M.; J . Environ, Qual . , 5, 15 (1976).

BOLT, G.H,, SUMMER, M.E. and Ki«DHORST, A.; Soil Sc i . Soc, Am. P r o c , 27, 298 (1963).

BOWMAN, R.S . , ESSINGTON, M.E. and O'CONNOR, G.A,; Soi l Sc i . Soc. Am, J . , 45, 860 (1981).

BRADY, N.C.; The nature and proper t ies of s o i l s , 8th edn. MacMillan Publishing Co., I n c . , New York (1974),

BREMNER, J.M.; J , Agric, S c i , , 46, 247 (1955).

BREMNER, J.M.; Organic ni trogen i n s o i l s . In W.V. BARHOLOMEW and F.E. CLARK, eds, "Soil Nitrogen, Am, Soc. Agron, I n c , , Madison, Wise, p , 93 (1965).

BREMNER, M., NIEDER WIESER, A. and PATAKI, G.; Experlmentia, 17, 145 (1961).

BROWN, D.S. and MILLER, R .J . ; Soil Sc i . S6c. Am. Proc . , 35, 705 (1971).

SURGES, A.; Sc i . Proc, R. Dublin Soc, , Ser, A, 1(4) , 53 (1966),

CAMERON, R.E. and FULLER, W.H.j Soil Sc i , Soc, Am, P r o c , 24, 353 (1960).

CARRINGER, R.D. and WEBER, J . B . ; Proc. South Weed. Sci , S o c , 27, 332 (1974),

CARTWRIGHT, B , , MERRY, R,H, and TILLER, K.G,; Aust. J , Soi l Res , , 15, 69 (1977),

CHESHIRE, M.V. and MUNDIE, CM.; Biochem. J . , 96, 38 (1965).

CLINE, G.R. and O'CONNOR, G.A.; Soi l S c i . , 138, 248 (1984),

CLOTHIER, B,E, , SCOTTER, D.R. and KERR, J . P . ; Soil S c i . , 123, 392 (1977).

47

CURTIN, D. , RAYON, J . and CHAUDHARY, R.A.; Soi l Sc i . Soc. Am. J . , 44(4) , 947 (1980).

DAVIDSON, J.M. and SANTEmANN, P.W.; Weed S c i . , 16, 544 (1968).

DEDEK, W., GRAHL, R. and MOTHES, B . ; J , Chromatogr., 331(1), 200 (1985).

DIJKSHOORN, W., VAN ROEKHDVEN, L.W. and LAMPLE, J.E.M.; Neth. J . Agric. S c i . , 21, 241 (1979).

DIX, H.M.; Environmental P o l l u t . , Atmosphere, Land, Water and Noise, John Willey & Sons, New York (1981).

DONAHJE, R.L., MILLER, R.W. and SICKLUNA, J .C . j So i l s : An in t roduct ion to so i l and plant growth. IV edn., Prent ice Hal l , I n c . , Englewood C l i f f s , N.J. (1977).

DORMAAR, J . F . ; Soi l S c i . , 103, 417 (1967).

DOWDELL, R.J . and SMITH, K.A.; J . So^il S c i , , 25, 231 (1974).

DUGGAN, R.E.; Pes t i c . Monit. J . , 1, 3 (1968).

ELLIOTT, H.A. and HUANG, C.P.; J . Colloid In t e r f . S c i . , 70(1) , 29 (1979).

FINLAYSON, D.G. and MacCARTY, H.R.j Res. Rev. 9 , 114 (1965).

FLAIG, W. and BBUTELSPACHER, J . ; Inves t iga t ions of faumic acids with ana ly t i ca l u l t racen t r i fuge . I n Isotopes and rad ia t ion in s o i l organic matter s tud ies . In te rna t iona l Atomic Energy Agency, Vienna (1968).

FLAIG, W., BEUTELSPACHER, H. and RIETZ, E . ; Chemical composition and physical proper t ies of humic substances, In s o i l components. Vol, 1, organic components, J .E . Gieseking ( e d . ) . Springer- Verlag, New York (1975).

FORBES, E.A.- POSNER, A.M. and QUIRK, J . P . ; J , Soi l S c i . , 27, 154 (1976).

FORBES, E.A., POSNER, A.M. and QUIRK, J . P . ; J, Colloid In te r face S c i . , 49, 403 (1974).

48

POROUGHI, J , ; Landwirtsch. Forsch. , 32, 37 (1976).

FRANKE, W.; Pes t i c . S c i . , 1, 164 (1970).

FRANZIN, W.G,, MOFARLANE, G.A. and LUTZ, A.; Environ, Sc i , Technol, , 13, 1513 (1979).

GAUR, A.C, and MISRA, K . C ; Plant So i l , A6, 5 (1977).

GHOSH, K,, and SCHNITZER, M,; So i l S c i . , 129, 266 (1980).

GIBBS, R . J . ; Geol. Soc, Am, B u l l , , 88, 829 (1977).

GILES, C,H,, MacEWAN, T.H,, NAKHWA, S.N, and SMITH, D. J , Chcm. S o c , 3973 (1960).

GINZBURG, I . I . J Pr incip les of geochemical prospecting techniques for non-ferrous ores and ra re metals . Pai^mon Press , New York, Chap. 2 (I96O).

GLASSTONE, S. ; Text book of Physical Chemistry, MacMillan and Co. L td . , London (I960).

GOH, K.M., RAFTER, T.A., STOUT, J.D. and WALKER, T.W.; J . So i l S c i . , 27, 89 (1976).

GOODMAN, B.A.; ACS Symp, S e r , , 323 (Geochem, Processes Miner. S u r f . ) , 342 (1986),

GOODMAN, G.T. and ROBERTS, T,M.; Nature, 231, 287 (1972).

GORING, C.A.I.J Ann. Review Phytopathol. , 5, 285 (1967).

GOWDA, T.K.S., SIDDARAMAPPA, R. and SETHUNATHAN, N.; Soi l Bio l . Biochem., 8, 435 (1976).

GREENLAND, D . J . , LABY, R.H. and QUIRK, J . P . ; Trans. Faraday Soc. , 58, 829 (1962).

GREGSON, S.K. and ALLOWAY, B . J . ; J . So i l S c i . , 35, 55 (1984).

GRIFFIN, R.A. and AU, A.K.; Soil Sc i . Soc. Am. Proc , , 41, 880 (1977).

49

GRIM, R.E., BRAY, R.M. and BRADLEY, W.F.; Am. Mineral . , 22, 813 (1937).

GRIM, R.E.; Clay mineralogy, McGrav H i l l , London, Chap. IV (1953).

GRIMME, H.f Z. Pflanzem. Dung, Bodenk,, 121, 58 (1968).

GROVER, R.; Can. J . Soi l S c i . , 53, 307 (1973).

GRUNER, J.W.; Am. Miner., 19, 557 (1934).

GRUNER, J.W.; Z. K r i s t , , 83 , 74 (1932).

GUPTA, U . C ; In , McUREN and PETERSON, eds . , "Soil Biochemistry", Marcel Dekker, I nc . New York, p . 91 (1967).

GUPTA, U.C. and SOWDEN, F . J . ; Soil S c i . , 96, 217 (1963).

HARRIS, C . I . ; Weeds, 15, 214 (I967).

HARRIS, C.R. and SANS, R.W.;Pe3t Mont. J . , 3 , 182 (I969) .

HELUNG, C.S.; Soi l Sc i . Am, Proc , , 35, 732 (1971a).

Soil Sci. Soc. Am. Proc., 35, 737 (1971b).

Soil Sci. Soc. Am, Proc,, 35, 743 (1971c).

HELLING, C.S.; Res. Rev., 32, 175 (1970),

HELLING, C.S. and TURNER, B.C.; Science, 162, 562 (I968).

HENDRICKS, S.B.; J, Geol,, 50, 276 (1942).

HENDRICKS, S.B.; II. Phys, Chem., 45, 65 (194A).

HENDRICKS, S.B.; J, Geol., 50, 276 (1947).

HENDRICKS, S.B. and JEFFERSON, M.E.; Am, Mineral,, 23, 863 (1938).

HBUPER, W.E., and CONWAY, W.D.j "Chemical Carcinogeneses and Cancer". Charles Thomas, Springfield, III. (1964).

HELUNG, C.S.

HELLING, C.S.

50

HODGSON, J.F.; Adv. Agron., 15, 119 (1963).

HOfWANN, U., ENDELL, K. and Wim, D.; Z. Kriat., 86, 3 ^ (1933).

HOROWITZ, M.; Ann. Report Project A10-CR-68, Graht PG-IS-2A8, Agricul. Research Service, US Department of Agriculture (1968).

HSU, P.H., and BATES, T.F.; Proc. Nat. Conf. Clays Clay Miner., 11, 299 (1963).

HULPKE, H.; Qual. Plant Water Veg., 19, 333 (1970).

JAMES, R.O. and HEALY, T.W.; J. Coll. Interface Scl., 40, 42 (1972).

JARVIS, S.C. and JONES, L.H.P.; J, Soil. Sci., 31, 469 (1980),

JOFFE, J.S.; Pedology, Rutgers University Press, New Brunswick, N.J. (1936).

JONG, E. De'.t Soil Sci,, 131, 34 (1981).

JORDAN, L .S . , FARMER, W. J . , GODDIN, J.R. and DAY, B.E.; Res. Rev., 32, 267 (1970).

JOSHI, D.C.; Plant S o i l . , 94(3) , 357 (1986).

KASER, H.; Ann. Phys., 14, 451 (1881). KAY, B.D, and ELRICK, D.E., Soil Sci., 104, 314 (I967).

KEREN, R.j Clay and Clay miner., 27, 303 (1979).

KHAN, D.V.; Dokl Vsesoyuz. Akad. S. Kh. Nauk Lenina., 7, 8 (1945).

KHAN, S. and BANSAL, Y.; J. Colloid Interface Sci,, 78,554 (1980).

KHAN, S. and KHAN, N.N.; Soil Sci., 142, 214 (1986).

KHAN, S., KHAN, N.N. and IQBAL, N.; Indian Soc. Soil Sci., 33, 779 (1985).

KIUiAM, O.W. and ALEXANDER, M.; Soil Sci., 132, 419 (1984).

51

KOONS, R.D., KELWKE, R.A. and JACKSON, M.L.; Soil Sci. Soc, Am. J., Uk, 155 (1980).

KRAHNE, D., SCHMIDT, S. and KUHN, H.G.j Fetle Scifen, Austri. Chan., 79(1), 32 (1977).

KRISHNAMURTHY, G.; Indian J. Farm Chem., 1(1), 6 (1983).

KUO, S. and BAKER, A.S,, Soil Sci. Soc. Am. J., 44 (4), 969 (1980).

LAGERWERFF, J.V,; Plant and Soil., 31, 77 (1969).

LAGERWERFF, J.V, and BRDWER, D.L.; Soil Sci, Soc. Am. Proc, 36, 734 (1972).

LAUWERYS, R., BERNARD, A., BUCHET, J.P. and R0EI3H, H; Control Heavy Met. Environ, Int. Conf,, I9 (1979).

LEENHEER, J.A, and AHLRICHS, J.L., Soil Sci. Soc, Am. Proc, 35, 700 (1971).

LINKSON, H.F., HEINEN, W. and STOFFERS, A.L.; Residue. Rev., 8, 136 (1965).

LUDWICK, A.G., ALDRICH, L., LUDWICK, N.K. and LARRY, M.; J. Assoc, Off. Anal Chem., 60(5), 1077 (1977).

LUXMOORE, R.J., VAN ROOYAN, D.J., HOLE, F.D., MANKIN, J.B. and GOLDSTEIN, R.A.; Soil Sci., 123, 77 (l977).

MABGDEFRALI, E. and HOFWANN, U.; Z, Krist,, 98, 299 (1957).

MARSHALL, C.E.; Z. Krist., 71, 433 (1935).

M/vRSHALL, C.E,; The physical chemistry and mineralogy. Vol. I, John Wiley, New York (1964),

MATTIGOD, S.V. and SPOSITO, G.; Soil Sci, Soc. Am, J, 41, 1092 (1977).

MAYLAND, H.F,, MUNTOSH, T.H. and FULLER, W.H.; Soil Sci. Soc. Am. Proc, 30(1), 56 (1966).

52

MCLAREN, R.G, and CRAWFORD, D.Y.j J. Soil Sci., 24, 172 (1973).

McNEAL, B.L.; Soil Sci. Soc. Am, Proc., 32, 119 (1968).

MEHLICH, A.; Soil Sci., 3, 361 (1962).

MELLANBY, K.j ' Pesticides and Pollution Collins' (1972).

MENZIE, M.; Metabolism of Pesticides: Special Scientific Report Wildlife No. 127, Washington (I969).

MUKHERJEE, P.N. and LAHIRI, A.; Fuel, 37, 220 (1958).

NAKANO, M.; Soil Sci., 124, 67 (1977).

NASH, R.G. and BEALL, M.L.; Science, 168, 1109 (1970).

NEWMAN, R.H. and TATE, K.R.; J. Soil Sci., 35, 47 (1984).

NRC (National Research Council); Committee on Medical and Biological' Effects of Environmental Pollutants. Nickel, Washington, D.C., Natl. Acad. Sci., 277 (1975).

O'CONNOR, G.A., ESSINGTON, H.E., ELRASHIDI, M. and BOWMN, R.S.j Soil Sci., 135, 228 (1983).

ORMROD, D.P.; Water, Air, Soil Pollut., 8, 263 (1977).

PAGE, A.L. and CHANG, A.C.j Proc, Sec, Nat, Conf, of Water Reuse: Water Interface with Energy, Air and Solids, Sponsored by Am. Inst. Chem. Engg, and U.S.EPA 4-8 May, Chicago, III, (1975).

PARR, J.F.; Effects of pesticides on microorganisms in soil and water, In pesticides in soil and water, W.D. Guenzi (ed.) Soil Sci, Soc. Am, Madison, USA, pp, 315-40 (1974),

PAULING, L.; Proc. Natl, Acad, Sci, U.S., 16, 578 (1930).

PEPPER, I.L. and MILLER, R.H.; Soil, Sci,, 126 (1), 9 (1978),

PRIBYL, J. and HERSEL, F.; 2, Anal, Chem., 286 (1), 98 (1977),

53

PUTMAN, H.D. and SCHMIDT, E.L.; Soil Sci., 87, 22 (1959).

REDDY, K.S. and GAMBRELL, R.P.; Agric. Ecosyst. Environ. 18 (3), 231 (1987).

REDDY, K.R. and PATRICK, Jr., W.H.j Soil Sci., 128, 60 (1979).

REICH, M. and BARTHA, R.; Soil Sci. 124(3), 177 (1977).

RICHARD, D.T, and NRIAGU. J.O.; Aqueous environmental chemistry of lead. In the Biogeochemistry of Lead in the environment, J.O. Nriagu (ed.), Elsevier/Holland, 219 (1978).

RICK, S.K., SLIFE, F.W. and BANWART, W.L.; Weed Sci., 35(2), 282 (1987).

ROBINSON, J.; Ann. Rev. Phannacology, 10, 353 (1970).

RODGERS, E.G.; Weed Sci., 16, 117 (1968).

RUSSELL, E.J, and APPLEYARD, A.; J. Agric. Sci., 7, 1 (1915).

RUSSELL, E.W,; Soil conditions and plant growth, Longmans, London (1973).

SADIQ-, M. and ENFIELD, C.G,; Soil Sci., 138, 262 (1984).

SANTILLAN-MEDRANO, J , and JURINAK, J . J . ; Soi l Sc i . Soc. Am, Proc. , 39 , 851 (1975).

SCHMITT, N., PHILUON, J . J . , LARSEN, A.A., HARNADEK, M. and LYNCH, A.J , ; Can. Med. Assoc. J . , 121(11), 1474 (1979).

SCHNITZER, M, and GHOSH, K.; J . Indian Chem. S o c , 56(2), 1054 (1979).

SCHNITZER, M. and KHAN, S.U.; Humic substances in t he Environment, Marcel Dekker, New York (1972),

SCHNITZER, M. and SKINNER, S.J.M.; Soi l S c i . , 103, 247 (1967).

SCHRAMM, L.L. and KWAK , J .C .T . ; Soil S c i . , 137, 1 (198^).

54

SCHRELBER, L.R., HOCK, W.K. and ROBERTS, B.R.; Phytopathol. , 61 , 1312 (1971).

SCHWARTZ, S.M., VARNER, J .E , and MARTIN, W.P.; Soi l Sc i . Soc. Am. Proc . , 18, 174 (1954).

SCHWERmANN, U. and FISCHER, W.R.; Geoderma, 10, 237 (1973).

oCOTT, D.C. and WEBER, J . B . ; Soi l S c i . , lo4, 151 (1966).

SHANNON, G.M.,. PETERSON. R.E, and SHOTWELL, O.L.; J . Assoc. Off. Anal. Chem., 68(6), 1126 (1985).

SILLEN, L.G. and MARTELL, A.E.; S t a b i l i t y constants of metal ion complexes - supplement no, 1 Chemical Soc. Special Publ. n o . 25, London (1971).

SINGH, M. and SINGH, N.; Soi l S c i . , 126(5), 255 (1977).

SINGH, R.P. , SAXENA, S.K, and KUMARI, K.; J . U q , Chromatogr., 8 (7 ) , 1319 (1985).

SINGHAL, J . P . and BANSAL, V.; Soil S c i , , 126, 36o (1978).

SINGHAL, J . P . , KHAN, S.U. and BANSAL, O.P.; J , Inorg. Nucl, Chem., 38 , 2297 (1976).

SINGHAL, J . P . and KUI4AR, D. . ; Clay & Clay minerals , 24, 122 (1976).

SINGHAL, J . P . , SINGH, N. and SINGH, R.P.; J . Indian Chem. S o c , 54, 457 (1977).

SMITH, H.A. and FU2EK, J . P . ; J . Amer. Chem. Soc, , 68, 289 ( 1 9 ^ ) .

SMITH, K.A.; Soil S c i . , 123, 284 (1977).

SOJKA, R.E. , SCOTT, H.D., FERGUSON, J.A. and RUTIEDGE, E.M,; So i l S c i . , 123, 182 (1977).

STEVENSON, F . J . ; Soil S c i , , 123, 10 (1977),

55

STEVENSON, F . J . ; Soi l Sc i , Soc, Am, Proc . , 20, 201 (1956).

STEVENSON, F . J . and GOH, K.M.j Geochim. Cosmochim. Acta. , 35, 471 (1971).

STOLLER, E.W.; Plant phys io l , , 46, 732 (1970).

STOVER, R . C , SCMMERS, L.E. and SILVIERA, J . J . ; J , Water Po l lu t . Control , Fed,, A8, 2165 (1976),

SYERS, J .K. , ADAMS, J.A. and WAUKER, T.W.; J , Soil S c i . , 21, 146 (1970).

TAKIJIMA, Y.; Soil Sc i , Plant Nutr. (Japan), 7, 80 (1961).

TAN, K.H.; Soi l S c i , , 125, 351 (1978).

TILLER, K.G,, NAYYAR, V.K. and CLAYTON, P.M.; Aust. J. Soil Res., 17, 17 (1979).

TILLS, A.R. and ALLOWAY, B.J.; J, Soil Sci., 34, 769 (1983).

TOTH, S.J.; Am, Water Works Assoc. J,, 60, 455 (1968).

VAN-OLPHEN, H.; Introduction to clay colloid chem. Interscience ' publishers, N.Y. (1963).

VISSER, S.A.; J. Soil Sci., 15, 202 (1964).

VLASSAK, K.; Soil Sci. Annual., 26, I9I (1975).

WAINWRIGHT, M.; Plant Soil, 55, 199 (1980),

WAINWRIGHT, M.; J. Soil Sci,, 29, 287 (1978),

WAKSMAN, S.A,; Humus: Origin, Chemical Composition and importance in nature. The Williams and WilidLns Co, Baltimore, Md, (1936).

WARE, G.W.; The pesticide book, W.H. Freeman and Company, San Fransisco (1978).

5G

WASEFMANN, M., WASERMANN, D., ZELLERMAYER, L. and CONE, M.; Pestic Monit. J., 1, 15 (1967).

WAITER, F.L. and GRUSSENDORF, O.W.; J. Econ. Entomol., 62(5), 1101 (1969).

WEBER, J.B.; Adv. Chem, Ser. No, 111, 55 (1972).

WEBER, J.B.; Soil Sci, Soc. Am. Proc., 3^, A0I (1970).

WEBER, J.B.; Am. Mineral., 51, 1657 (1966).

WEBCER, J.B., WEED, S.B. and WARD, T.M.; Weed. Sci., 17, 417 (1969).

WILLIAMS, D.E., VLAMIS, J., RJKITE, A.H. and COREY, J.E.; Soil Sci., 129, 119 (1980).

WILSON, M.A.; J. Soil Sci., 32, 167 (1981).

WILSON, M.A. and GOH, KM,; J. Soil Sci., 34, 305 (1983).

WILSON, M.A., COLLIN, P.J. and TATE, K.R.; J. Soil Sci., 34, 297 (1983).

YOSHIDA, H. and NAKADATE, K.; Soil Sci. Plant Nutr. (Japan), 10, 38 (1964).

ZUNINO, H. and MARTIN, J.P.; Soil Sci., 123(2), 65 (1977).

ZYRIN, N.G.; Vestn. Mos, Kor. Uny. 1 (1948).

CHAPTER - I

THE IKrLUEKCE OF ORGANIC ACIDS AND BASES ON TliE MOBILITY

OF SOME HEAVY MET'ALS THROUGH ALIGARH SOIL BY

SOIL THIN LAYER CHROMATOGRAPHY

57

INTRODUCTION

Among various organic compounds, carboxylic acids

(Schwartz et al„,l954), amino acids (Rending, 1951; Sowdens, 1956)

and organic bases like nicotine (Shtompel, 1981; Hanks et al<, 1980

and pyridine (Hanks et al., 1980; Vasil'Chenko et al.-1975;

Martin, 1977) have been found to occur or used in soils.

These organic compounds are found to interact with soil

colloids (Smith, 1934; Greenland et al,jl962; Brindley and Moll,

1965; Khan and Singhal, 1967; Theng, 1974) which may affect the

metal translocation and influence their availability to plants.

However, their specific role in the translocation of heavy metals

has not yet been attempted. Recently Khan et al, (1982) have re­

ported that the heavy metals translocate in the soil as metal-soil

organic matter (SOM) complexes and emphasized the importance of

organic compound in the translocation of heavy metals. The purpose

of this study is to understand the role of certain organic com­

pounds e.g. carboxylic acids, amino acids and organic bases in the

mobilization of certain heavy metals like Pb, Cd, Ni, Hg and Ag which

are of polluting nature using soil thin layer chromatography. The

present study may be useful in understanding the behaviour of other

organic chemicals having similar functional groups in the metal

translocation through soils.

58

EXPERIMENTAL

(A) DETERMINATIOn OF MECHANICAL COMPOSITION OF THE SOIL

The mechanical composition of the Aligarh soil was deter­

mined by International pipette method (Piper, 1950). For this,

a 10g soil sample (passed through 7 mesh BSS sieve), was dispers­

ed in water after treatment with 30? 2^P ^° remove any organic

matter and 0.2N HCl and 50 ml sodium oxalate (8g/ litre) as dis­

persing agent. The percentage of coarse, medium and fine sand

was calculated from the weight of residue left behind on 25, 72

and 200 mesh sieves (BSS), The suspension was diluted to 500 ml

and transferred to a graduated boiling tube which was immersed in a

constant temperature water bath at 25 + 1 C throughout the course

of pipetting. A 10 ml sample was pipetted out carefully at speci­

fied intervals of time from a depth of 10 cm. It was dried and

weigiied. Tlie percunLage of medium silt, fine silt and clay

were then calculated from the weights of residues. The percentage

of coarse silt was calculated by substracting the sum of the per­

centage of all the fractions given above from hundred. The

results of mechanical analysis are: Sand: 60,^YQ, Silt: 25,5% and

clay:M'/o

(B) DETERMINATION OF pH

The pH of the soil was determined with Elico pH meter,

model L.-10, with glass and saturated calomel electrodes assembly.

5!)

A 1:2,5 soil: water ratio suspension was used for measuring

the pH of the soil. The pH of the soil was found to be 8.8,

(C) PETERlVilNATION OB' ELECTRICAL CONDUCTIVITY

The electrical conductivity of the soil was measured with

Phillips conductivity bridge and dip type cell at 30 + 1 C.

A 1:2.5 soil: water ratio was use for the measurement. The

-4 -1 electrical conductivity of soil was 4.8 x 10 mhos cm .

(D) DETERMINATION OF ORGANIC MATTER

The soil organic matter content of the soil was detennined

by the method of Walkley (1947) as follows:

Reagents required

1N pot*assium dichromate, cone, sulphuric acid, 85% sulphuric acid and

phosphoric acid, 1% diphenylaniine indicator in^ water . N/2

ferrous ammonium sulphate solution.

Procedure

A 2 g of soil sample was taken in 500 ml conical flask,

10 ml of N potassium dichromate solution and 20 ml of conCo sul­

phuric acid were added. The flask was shaken gently several

times and allov/ed to stand for 30 minutes and thereafter 200 ml

of distilled water, 10 ml of phosphoric acid, and 1 ml of di-

phenylaudne indicator were added to it. The amount of unreacted

60

potassium dichromate was titrated against standard N/2 ferrous

ammonium sulphate solution till the violet colour change to pur­

ple, and finally to green. Reagents blank determination was

also carried out in the same manner. From the volume of dichro­

mate solution used for oxidation, organic carbon was calculated

by the expression:

Organic carbon = (Blank litre - Actual litre} x 0,003 x M weight of dry soil in g.

wiiere M is concentration of ferrous ammonium sulphate. The value

of organic carbon was converted to organic matter by multiplying

witij the factor 1,724. The organic matter content of Aligarh

soil was found to be 0,4o%,

(E) DETERMINATION OF CATION EXCHANGE CAPACITY

Tlio cation exchange ca[)acity of the soil was determined

by the method of Jackson (1958).

Reagents required

0.05N hydrochloric acid, IN sodium acetate (pH 5), 1N

calcium cixloride solution, EDTA solution, ^% solution of erio-

chrome black 'T' in ethanol, buffer (pH 10), 2% sodium cyanide

solution.

Procedure

A 5g soil sample was taken in a 100 ml conical flask and

61

tlie soluble salts were washed out by treating the soil with

0.05N HCl and finally with distilled water. It was furtiier

treated with 1N sodium acetate of pH 5 for 30 minutes with inter­

mittent stirring. This acidified sample was given five washings

with 1N standard calcium cliloride solution„ The excess salt was

removed by washing with 80% aqueous acetone solution untill the

excess CaClp is removed, as indicated by a negative AgNO^ test

for chloride ion in the final washing. The calcium ions were

exchanged from Ca saturated soils by means of exchanging it with

a neutral 1N sodium acetate solution. The washings were collected

and utilized in the determination of exciianged Ca by titrating

it with a standard EDTA solution, using 10 ml of the NH^Cl-NH^OH

buffer of pH-10 and eriochrome black 'T' indicator with 1 ml of

2/0 NaCN solution as masking agent for interfering ions, A reagent

blank was also run simultaneously to avoid any error due to impu­

rities. The blank readings were substracted from the readings of

calcium determination. From the volume of the EDTA used, the

values of cation exchange capacity was calculated by using the

expression:

„ , .. V X N X 100 Exchange capacity = — r - r z — T - r , T^—: ( in meq. per weight of the so i l m g. 100 g so i l )

where, V is the volume of EDTA, N is the normality of EDTA solu­

tion used. The cation exchange capacity of Aligarh soil was deter­

mined to be 16.3 meq per 100 g soil.

62

(F) DETEmiNATION OF EXCHANGEABLE CATIONS

A 50 g air dried soil sample was taken intp a 250 ml

conical flask and a 100 ml of 1N NH^OAc was added to it. The flask

was covered with a stopper and was shaken for 20 minutes and then

allowed to stand overnight. The contents of the flask were then

transferred into a buckner funnel in which a moist Whatman filter

paper (no. 42) had been seated by gentle suction. The soil was leach­

ed with an additional 400 ml of NH^OAc, The filtrate containing

NHiOAc extract of soil was evaporated to dryness on a steam plate.

If the residue is dark in colour (indicating organic matter), it is

again treated with 2 ml of 30j6 JLOg and 2 ml of 6N HNO, and heated

to dryness on a steam plate» The dried residue was dissolved in 10

ml of 6N H:I and diluted with distilled water. It was filtered

through Whatman filter paper (no. 42) and the volume was made upto

100 ml.

Exchangeable calcium plus magnesium was estimated in the

known volume of filtrate by EDTA titration with eriochrome black

•T' indicator. Calcium was also estimated separately by using mu-

rexide indicator with 10J KOH as recommended by Jackson (1958). The

volume of EDTA for magnesium was calculated by substracting the

volume for calcium from the volume of calcium plus magnesium used.

The exchangeable sodium and potassium were estimated in

solution by using 'Systronicks' flame photometer. Standard curve

for sodium (0»50 fig) and potassium {0-^ /ug) were drawn (Fig. 4)

and the amounts of Na and K in solution were estimated by using

these curves. The exchangeable Ca "*", Mg '*', Na"*" and K* were found

tOOr

c

o

0 [0 20 20 40 SO Concentt^ation oF Sodium In ppm

1 I I I L \0 ZO 30 40 50

concentration of Potassium in ppm

FIG.4-STANDARD CURVES FOR SODIUM AND POTASSIUM BY FLAME PHOTOMETER.

63

to be 3.5, 1.2, 3.0 and 0,5 meq. per 100 g soil respectively.

(a) MOBILITY (Rf.) DETERMINATION BY SOIL THIN LAYER CHROMATOGRAPHY

Apparatus and reagents

TLC applicator with adjustable thickness_,uniform glass

plates (20x20 cm), glass chambers with cover, glass sprayer,

100 mesh sieve (BSS).

A 0.1M nitrate solutions of lead, cadmium, nickel, mercury

and silver in distilled water, 0.5% (w/v) ethanolic solution of

haematoxylene, dimethyl glyoxioe, and 1% (w/v) dithizone solu­

tion in CCl, etc.

Preparation of plates

For the measurement of R^ values, the soil samples were

ground and passed through 100 mesh sieve (BSS) to obtain a homo­

geneous particle size ( 150 ju).

A slurry of prewashed soil sample (free from soluble salts)

was prepared in distilled water with a soil water ratio of 1:2

in each case. Glass plates were cleaned with detergent solution,

water and with 50% methanol-water acidified with hydrochloric

acid, and finally the plates were wiped with cotton soaked with

hexane. These glass plates were coated with slurries of soil

sample to a thickness of 0,5 mm with the help of TLC applicator.

64

Tile prepared plates were kept on a rack and were allowed to dry

in the air at room temperature overnight. Two lines at 3 cm and

13 cm above the base were scribed so that the standard development

distance of 10 cm was used on all the plates,

APPLICATION OF SAMPLE AND DEVELOmENT OF PLATES

k 6 pi nitrate solution (O.IM) of heavy metals was applied

on the base line of TLC plate in a single application with the

help of micropipette. The plates were then developed with distill­

ed water or amended distilled water upto the upper line on the

plates in a closed glass chambers by ascending chromatography.

To prevent disintegration of soil in contact with water, wet

strips of filter paper about 2,5 cm wide were wrapped around the

bottom of the plate before the development,

DRYING AND DETECTION OF CHROMATOGBLAMS

The developed plates were air dried at room temperature

(30 C). Visualization of heaA/y metals i,e, Pb, Hg and Ag; was

made by spraying 0,% (w/v) ethanolic solution of haematoxyiene

as a violet colour spot of metal-haematoxyiene complex which

remained stable for about 10 hours. While Ni, and Cd were detected

as red colour spots of Ni-glyoxime, and Cd- dithizonate complexes

by spraying dimethyl glyoxime and ^% (w/v) dithizone in CCl/

respectively.

65

MEASUREMENT OF Rf - VALUES

The frontal R^- values (mobility) was measured by the

relation:

Value - ^^o^'tal distance moved by the metal^ ^ ~ ~ Frontal distance moved by the developer

FOR THE EFFECT OF ORGANIC MATTER

The soil was treated with :5CS ^J^2 ^° decompose soil

organic matter (SOM) according to the method of Jackson (1958).

The soil sample with and with decomposed SOM were used as static

phase on the TLC plates and distilled water as developer. The

results are given in Table-II.

FOR THE EFFECT OF ORGANIC ACIDS AND BASES

The calculated volume of aqueous solutions of different

acids like formic acid, acetic acid, oxalic acids and their

aqueous salt solution, Glycine, Alanine and Valine; Nicotine and

Pyridine were taken in jars. These solutions were used as

developer while natural soil as static phase. The results are

given in Table -III to XIII and Fig. 5-7.

RESULTS AND DISCUSSION

An examination of Table-II shows that the mobility of

heavy metals through soil with and without organic matter (30';o H2O2

66

t reatment) follows the order, Ni>Cd>Hg>Ag>Pb, The r e s u l t s

are in accordance with the e a r l i e r view of Khan et a l , (1982) and

Lund et a l . (1976) tha t the heavy metals move as t h e i r soluble

metal-SOM complexes in so i l according to t h e i r ion s ize (Table-I l )

and complexing nature . The decomposition of so i l organic matter

enhances the heavy metal mobili ty to subs tant ia te the clay-metal-

SOM in te rac t ions (Theng, 1974).

The effect of carboxylic acids on the mobility of heavy

metals i s given in Table- I l l to V and Fig, 5 which shows tha t the

mobil i ty increases with increase in the concentration of ac ids .

The heavy metal mobility in different acid media follows the order

f o r m i c > a c e t i c > o x a l i c acids which may be a t t r ibu ted to the solu­

b i l i t y of metal carboxylate (Table- I I ) , The r e l a t i v e order of t h e i r

mobili ty in the acid medium was Ni>Cd>Hg>Ag>Pb except in the

case of ace t ic acid in which the order being Hg>Cd>Ni>Ag>Pb

which i s in the reverse order of the i n s t a b i l i t y constants of t h e i r

ace ta te s a l t s . Thus the ion s i ze , i n s t a b i l i t y constants and solu­

b i l i t y of metal carboxylates seem to determine the extent of t h e i r

mobil i ty tlrirough s o i l .

The r e s u l t s were further ver i f ied with the sodium carboxy­

l a t e systems (Table VI to VIII and Fig, 6) which show tha t the

addi t ion of sodium carboxylates enhances the heavy metal mobility

approximately equal to tha t of carboxylic ac ids . The t r ans loca ­

t i o n in presence of organic acids and t h e i r s a l t s could be explain­

ed by considering the re lease of heavy-metals from adsorptive

67

sites of soil colloids due to the preferential adsorption of + +

H or Na resulting the formation of metal carboxylates which

may move through soil. The probable reaction mechanism can be

given as follows:

The carboxylic acids or their sodium salts ionize to

give:

Hm X -- ^ mH^ + X ""

Na^ X ^ - m Na" + x" "

The H or Na replaces the heavy metal ions from soil colloids

as:

+ \ . „u / M \ „ .,n+/ MCH^O) - Yn + nH"*" (or Na ) ::^=^ "H (or Na) -Y + IT'^ili^O)

In acid systems, the pH of the s o i l decreases from 8,8 tovxN3,0.

The heavy metals remain in t h e i r ionic form and combines with

carboxylate ions as

m

mM "" + n X° - : ; r - r ^ /"MmXn 7 ° I I

mM'"*- + ( n + 1 ) x " ' - ^ i z ^ /-MmX(n + i ) 7"*" H I

The metal-carboxylatcs (I to I I I ) so fonned moved tiirough

t h e s o i l . Moreover, the increased concentration of carboxylate

•« <^

'_ TN

t -•r

l^

c 1 -

'x r. • ^ H O ' 0

• - T 1 < — 1

a o s H rO

i f3 • "H

S f l U rj4

o H H >H

H

' a W H >-J rQ

m o r J

^ w K EH

#—* O

S E-i EH • i ; • . • *

o M / • — «

• j ;

Q a: o ^A H O CO

ft, o GH

P ft^ rt< rq f : [:: EH

I 1

)

» \

« W H •C

^ X O

(5 0

^ a w u: EH

f n 0

>H

H a M

m 3 8 1

j i (O EH

^ H CO

0

> H

EH

a H

^ EH : 0

^ Hi

- — « r -

1 UO 0 0 T—

t.O

^

ii •H

>> -P •H H •H

H 0 CO

cu •p

i H Cd CO r-) P C\] <U X

•J: 0

01 p

ra - p - p (U 0 0

a oJ

CO

H cU

3g cu 0

A * H

0) 4->

•H <U H - P 0

cU-P H -P w cti to G - p 0 0 <D

M 0 a

N +3 0 •H (!)

w goo a 0

C fn ^ 0 cd

M a x

to 0) :3

H

rt >

t

1 tH

cd

•P 3 0

- p •H 0 •^•r\ U

n a p • r i bD-P 0 (u « j .

CO 0 e

A H

-P •H 0 : 5 - H ?H

d QJ H ro -P •H bO-P 0 fn c

CO 0 a

CO

•p 0) Q

p cS 0) Li

<u H ^ :3 H 0 to

fl i - l

• VO V -

0) H

H 0

CO

vo T -0

• 0

VO

C\J N^

» 0

CO r -

• 0

H 0)

^ 0

•r1 4 H

t ^ r<^

0 0

• 0

0) I-J

E?^ (1) 0

> CO

H

0) 0 > CO

C--•V-

0 0

« 0

i n

cr» CM

• 0

c^ T—

• 0

g 3 •H

^ 03 0

(U H ,Q :3 H 0 to

« M

l A

• 0

• 0

cr> 1 0 T -

X try I S

• m

l A

ITN CNJ

• 0

l A r -

• 0

>>. U 3 0

u QJ

»

\o X-

8 0

• 0

« l A

-J-

• r -

CO t A

0 •

0

<h

l A

— •

0

s •

0

T^ cd Q) •-J

-4-^ A 0 0 •

0

CM 0

• 0

1

r A CO r -

•

0

r A

T -

CNJ

• 0

r A r -

• 0

U 0)

> H •H

CO

-— MD VO cr> V -

N _ *

0 • d

g g Q)

ri<

• d

JH

<u to cu

•H ^1

Cx<

1

a

cr\ LA

cr. r -•—X

> 0)

• . --"x H VO • a vO to C7> cd V-

> ^ t 3 S

ro H (U

to TJ

•H c3 0 •r4 -P to to

p td 0 (U

>H :^:

1 1

p 0

68

69

TABLE - I I I

EFFECT OF FORMIC ACID ON THE MOBILITY (R^-VAIUES) OF HEAVY METALS THROUGH AUGARH SOIL.

R^-valuea Heavy ^ metals Formic acid 0.0 0,1 0.5 1.0 1.5 2.0

(moles/ l i t r e )

Nickel 0 .18 0.44 0.72 0.85 0.92 0.95

Cadmium 0.17 0.40 0.69 0.81 0.90 0.94

S i l v e r 0.13 0.31 0.51 0.58 0.65 0.71

Mercury 0.15 0.25 0.56 0.66 0.74 0.84

Lead 0.08 0.18 0.32 0.39 0.43 0,45

70

TABLE - IV

EFFECT OF ACETIC ACID ON THE MOBILITY (R -VAIXJES) OF HEAVY METALS THROUGH AUQARH SOIL.

R--value3 Heavy metals Acetic acid 0.0 0.1 0.5 1.0 1.5 2.0

(moles / l i t r e )

Nickel 0.18 0.57 0.63 0.76 0.77 0.78

Cadmium 0.17 0.56 0.66 0.79 0.82 0.85

S i l v e r 0.13 0.47 0.42 0.44 0.A6 0.50

Mercury 0.14 0.43 0.70 0.81 0.84 0.87

Lead 0,08 0.21 0.34 0.4o 0.46 0.48

71

TABLE - V

EFFECT OF OXALIC ACID ON THE MOBIUTY (Rj «VAUUE3) OF HEAVY METALS THROUGH ALIGARH SOIL,

R^-va lues Heavy ^

metals oxal ic acid 0.00 0.05 0,10 0.25 0.50 (moles/ l i t r e )

Nickel 0.18 0.19 0.24 0.35 0.41

Cadmium 0.17 0.15 0.18 0.33 0.4o

S i l v e r 0.13 0.12 0.17 0.25 0.31

Mercury 0.15 0.17 0.26 0.29 0.35

Lead 0.08 0.10 0.20 0.27 0.28

72

TABLE - VI

EFFECT OF SODIUM FDRHATE ON THE MOBILITY (R^-YALUSS) OF HEAVY

METALS THROUGH ALIGARH SOIL.

Heavy m e t a l s

R^ - va lues

Sodium formate 0 .0 0 ,1 0 . 5 1.0 1,5 2 .0 ( m o l e s / l i t r e )

Nicke l 0 .18 0,23 0,49 0.71 0.82 0 .88

Cadmium 0.17 0.26 0 .45 0 .64 0,70 0,77

S i l v e r 0 .13 0.17 0 .30 0.35 0.42 0 .54

Mercury 0.15 0 .15 0.23 0.27 0.20 0.22

Lead 0.08 0.09 0 .14 0.19 0 .24 0 .30

73

TABLE - VII

EFFECT OF SODIUM ACETATE ON THE MOBIUTY (R^-VAIUES) OF HEAVY METALS THROUGH AUGARH SOIL.

Heavy metals

R^- values

Sodium aceta te 0,0 0.1 0,5 1.0 1,5 (moles/ l i t r e )

Nickel 0.18 0.32 0.66 0.80 0,86

Cadmium 0.17 0.25 0.61 0,79 0,87

S i l v e r 0.13 0.24 0.37 0.44 0.43

Mercury 0.15 0.17 0.20 0.25 0.31

Lead 0.08 0.14 0.24 0.36 0.46

74

TABLE - VIII

EFFECT OF SODIUM OXALATE ON THE MOBILITY (R -VAUUES) OF HEAVY METALS THROUGH ALIGARH SOIL.

Heavy metals

Rj^-values

Sodium oxalate o.OO 0.05 0.10 0.25 0.50 (moles / l i t r e )

Nickel 0.18 0.2? 0.38 0.55 0,73

Cadmium 0.17 0.16 0.18 0.24 0.37

S i l v e r 0.13 0.11 0.12 0.15 0.11

Mercury 0,15 0.13 0,11 0.12 0,11

Lead 0.08 0.07 0.09 0.13 0.16

75

TABLE - IX

EFFECT OF GLYCINE ON THE MOBILITY (R -VALUES) OF HEAVY METALS THROUGH ALIGARH SOIL.

Heavy metals

R*-values

Glycine 0,00 0.01 0.05 0.10 (moles / l i t r e )

Nickel

CadmivuD

S i l v e r

Mercury

Lead

0.18

0.17

0.13

0.15

0.08

0.42

0.17

0.19

0.20

0.07

0.60

0.15

0.25

0.20

0.07

0.70

0.20

0.30

0.25

0.08

76

TABLE • X

EFFECT OF DL» ALANINE ON THE MOBILITY (R -VALUES) OF HEAVY METALS THROUGH ALIGARH SOIL.

R^-values Heavy * metals Dl- Alanine 0.00 0.01 0.05 0.10

(moles / l i t r e )

Nickel 0.18 0.52 0.80 0.89

Cadmium 0.17 0.17 0.18 0.21

S i l ve r 0.13 0.15 0.30 0.35

Mercury 0.15 0.15 0.3A 0.35

Lead 0.08 0.09 0.09 0.09

77

TABLE -

EFFECT OF VALINE ON THE MOBIUTY THROUGH ALIGARH SOIL.

Heavy metals y^ixne 0.00

(moles / l i t r e )

Nickel 0.18

Cadmium 0,17

S i l v e r 0.13

Mercury 0,15

Lead 0.08

XI

(R -VALUES) <

R--values

0.01

0.53

0.17

0.21

0.15

0.10

DF HEAVY

0.05

0.83

0.16

0.24

0.29

0.09

METALS

0.10

0.93

0.20

0.35

O.Ao

0.09

78

TABLE - XII

EFFECT OF NICOTINE ON THE MOBILITY (R -VALUES) OF HEAVY METALS THROUGH ALIGARH SOIL.

Heavy metals

R^- values

Nicotine 0.000 0.002 0.008 0.050 (moles / l i t r e )

Nickel 0.18 0.17 0.14 0.15

Cadmium 0.17 0.11 0.11 0.10

S i l v e r 0.13 0.09 0.08 0.08

Mercury 0.15 0.09 0.09 0.09

Lead 0.08 0.08 0.08 0.08

79

TABLE - XIII

EFFECT OF PYRIDINE ON Th£ MOBILITY (R^-VAIUES) OF HEAVY KETAL3 THROUGH ALIGARIi SOIL. ^

Heavy ^f " va lues m e t a l s

P y r i d i n e Q.OOG 0.002 0.008 0.050 m o l e s / l i t r e

Nicke l

Cadmium

S i l v e r

M ercury

Lead

0.18

0.17

0 .13

0 .15

0.08

0.17

0.16

0.11

0 .13

0.09

0.17

0.16

0 .11

0.11

0 .10

0.15

0.16

0.11

0.10

0 .10

o in

in

I

D

O

O t

O

in

in

d

o d

o

in

O

in

d

o

d

o E

•o

X o l_

n) O

c o

c o

o 3 O a: X ) -

CO

UJ

>-

>

^ I- <

— r

>-

CQ

O Z UJ

2

O

I/) O o <

o z < o Q: o UJ

Z o tn u_ O I-o UJ u.

O (/)

X cc <

UJ <

in

6 u.

x> Q.

X

C7>

<

X

C/5

,t-l-l

o lO d

tT) rvj

d

"^ o

o

o •

ro

in

—

o *^

in

d

o 6 o f \ j

in

9J

1 -4->

O G

1/)

ro

X o .a

u

6 ZJ

•a o

o

c o

4-<

t_ 4->

c

u c o

UJ

Z >-> < UJ X U-

o > •

1 -

_ J

5 o z UJ X 1 -

2

o I/)

U <

2 < O cc O u_ O

h-

< CO

D

Q O

_ l

O I/)

X cc < o - J

<

X I

a X

<

4

CT>

X

0

a

o d

in

d

o d

u. O X

o D -Z UJ O u . OC u - X UJ h -

z

d

X -1 O

vi * >t H

X -i

* X

5 X - 1

——>#6^-x

X H

Hf. X - I

X

^ X _ O

oo

6 o d o o 6

I/)

o d

o p

— d

m o 6

»— o d

r-"

d

in o

o

0 /

(-• • J

trt at

o

e

o c

<

w-o c o

L.

C a>

c o U

UJ

>• > < i j j

X

u_ O > h-

_J

CD O

z UJ

z o

Q — (J <

O z i < lU

5: o on

U-

o

H

UJ

_ J

O

X a: <

<

X o D O a: X

an

a. X

•s

en < 4

X

o

t ?

a *

»

z o

LU H-

u.

hi

80

ions favour the formation of -vely charged metal carboxylate (III)

which lowers the adsorption of these species over the -ve sites of

soil colloids and hence increased the mobility. The density of

the surface -ve charge on soil colloids is also enhanced due to

the adsorption of carboxylate ions over reactive sites as in the

case of other anions (Ra^jan and Fox, 1975).

While in the case of salt systems, the pH increased from

8.8 to 9.2. Most of the metal ions may be considered to remain

in the form of MOH (monovalent), MOH"^ and/or M(0H)2 (divalent)

which can form their respective metal carboxylates as

0 //

R - C - 0 ... H - 0 Ml

(IV)

R - C ^

0

(V)

H

I 0

M

and/or R - C y- H

0 .. H -0 -

0

M

(VI)

The hydrated metal-carboxylates (IV to VI) so formed move through

the soil. But as the salt concentration increased, the -vely

charged species (Vl) may favourably be formed which causes a lower

preference over the soil colloids and thus enliance the mobility.

81

The effect of some amino acids is given in Table-IX to

XI and Fig, 7 which shows that the mobility of heavy metals

generally increases with increase in the concentration of amino

acids. The order of heavy metal mobility in soils was found to

be valine >-alanine >. glycine which is in accordance with their

own mobility in soil (Singhal et al,, 1978) while the relative

order of the mobility of the heavy metals in soil was Ni>Hg>Ag>

Cd>Pb except in the case of glycine where the order being Ni

A-g>Hg>Cd>Pb, As the pH of the soil solution was alkaline

(8.3), the amino acids may be expected to remain in their anionic

forms (Theng, 1974) because pH •;> pi (isoelectric point). These

anionic forms of the amino acids may combine with the heavy metals

as H

0 .0''

R-CHNH - C + M(OH)'*' > R-CHNH - C 0

0" 0 M

(VII)

The instability constant of these metal-araino acid

complexes were reported (Yatsimirsku & Vasil'ev, 1959) in the

reverse order of the mobility. The larger molecular size of

amino acid restricts the adsorption of its metal complex on the

interlemeller surfaces(Talibuddin, 1955) and mobilize it faster.

Thus, the stability and size of heavy metal amino acid complex

(VII) decide the mobility of these metals in the soil environ­

ment.

82

The effect of organic bases such as nicotine and pyridine

on the mobility of heavy metals is given in Table-XII and XIII.

It is evident that the nicotine and pyridine have no marked

influence on the heavy metal translocation in soils. However, a

slight decrease in the mobility is observed in some cases which

may be attributed to the metal-base soil/clay complex formation.

As the pH of the system upon the addition of these bases remains

above 7 (8,3 in our case), the lone pair of nitrogen may attract

the heavy metals through hydrogen bonding (Singhal and Singh,

1972) as follows:

-N: + H O ,., H-OH-M-Yn 1 ^

1 -N ... H-O^-Yn + H2O

I (VIII)

(Where - N : = Q ) o r Q ^ - ^ ^ ^

heavy metal with n charge)

soil colloids and M is

Thus, the complexation of metal with bases and soil colloids

immobilized the heavy metals in soil.

83

REFERENCES

BRINDLEY, G.W. and MOLL, W.F. ( J r . ) ; Am. M i n e r a l o g i s t , 50 , 1355 (1965) .

FREISER, H. and FERNANDO, Q^; ' I o n i c e q u i l i b r i a i n a n a l y t i c a l c h e m i s t r y ' . New York, Wiley (196b) .

GREENLAND, D . J . , LABY, R.H. and QUIRK, J * P . ; T r a n s . Farad. S o c . , 5 8 , 829 (1962) .

HANKS, A.R., SCHRONK, L.R. and ARNST, T .C . ; . J . Liq . Chromat. , 3 ( 7 ) , 1087 (1980) .

c JACKSON, M.L.; ' S o i l Chemical A n a l y s i s ' , P r i n t i c e - H a l l , Englewood

C l i f f s . , N J . (1958) ,

KHAN, S . , NANDAN, D. and KHAN, N.N.; Environ. P o l l u t . (Se r . B ) , 4 ( 2 ) , 119 (1982) .

KHAN, S. and SINGHAL, J . P . ; S o i l S c i . , 104, 427 (1967) .

LUND, L . J . , PAGE, A.L. and NEI^ON, C O . ; J . Environ, Q u a l . , 5 , 330 (1976) .

MARTIN, F . , SAIZ-JIMENEZ, C. and CART, A.; S o i l S c i , Soc. Am. J . , 4 1 ( 6 ) , 1114 (1977) .

PIPER, C . S . ; ' S o i l and P lan t Ana lys i s ' Uny Adelaide Aust . (1950) .

RAJAN, S . S . S . and FOX, R.L . ; Proc . S o i l S c i . Soc, Am. 39 , 846 (1975) .

RENDING, V.V.; So i l S c i . , 7 1 , 253 (1951) .

SCHWARTZ, S.M., WARNER, J . E . and MARTIN, W.P.; S o i l S c i . Soc. Am. P r o c , 18, 174 (1954) .

SHTOMPEL, Ya.A., MURZINOVA, I . I . £md KOTSYUBA, M.A.; Agrokhimiya, 3 , 99 (1981) .

84

SINGHAL, J . P . , KHAN, S. and BANSAL, V.; P roc . I nd i an N a t l . S c i . Acad., Vf(5) , 267 (1978) .

SINGHAL, J . P . and SINGH, R . P . ; Ind ian J . Chem., 10, 1100 (1972) .

SMITH, C.R.; J . Am. Chem. S o c . , 56, 1561 (1934) .

SOVTOENS, F . J . ; S o i l S c i . , 82 , 491 (1956) .

TALIBUDDIN, 0 . ; Trans Farad. S o c , 5 1 , ^82 (1955) .

THENG, B.K.G.; The chemistry of c lay organic r e a c t i o n s (1 s t e d n . ) , London, Adam. Hi lge r (1974) .

VASIL'CHENKO, V . F . , ABRAMOVA, K.A., DUBR0V3KAYA, A.A. and II'NITSKAYA, L . P . ; Simp, S t r a n . Chlenov. SEV. I 0 t h , 2, 34 (1975) .

WALKLEY, A.; i b i d . , 63 , 251 (1947) .

WEAST, R.C., and SELBY, S.M.; Handbook of chemistrv and physics. (47th edn.). Ohio, Chemical Rubber Co, (1966)0

YATSIMIRSKU, K.B. and VASIL'ev, V.P.; Instability constants of complex compoundSo New York, Consultants Bureau Enterprises, Inc. (1959).

CHAPTER . I I

THE MOBIUTY OF PESTICIDES IN SOILS AS AFFECTED BY

THEIR CHEMICAL CHARACTERISTICS AND

SOME SOIL PROPERl'IES

85

INTROOJCTION

The study of pesticide mobility In so i l s i s an Important

phenomenon in understanding I t s effectiveness for bloactlvity in

so i l (Kurlekar and Khuspe, 1984)«, Various soil pax^umeters such

as soil organic matter and the i r fractions i«e humlc and fulvic

acids; nature of exchangeable cations over clay surfaces, clay

contents, soil pH and free metal oxides e tc . have been found to

influence the translocation of oirganic pesticides in soi ls

(Bailey and White, 1964j Neazpass, 1971; Singhal and Bansal, 1978).

I t has been observed that adsorption and desorption of organic

chaaicals in soi l are greatly influenced by the molecular s t ruc­

ture of the compound(Hortland, 1970),

Among pesticides selected for the study, Formothlon,

Malathion and Thiometon are organophosphorus Insecticides \fbich

are used for controlling the insect borne diseases in various

crops (Ghos, 1979; Deshmukh et a l . , I960; Thimmaiah and Thippes

Wamy, 1980). Whilst, Fluchloral.ln i s an halogen containing her­

bicide (Raghavaiah et a l . , 1980). The work on the translocation

of these chemicals as influenced by the i r chaaiical characterist ics

and soi l properties i s lacking in l i t e ra tu re . Therefore, i t was

thought worthwhile to conduct some experiments on the i r t rans lo­

cation in relation to soi l pollution caused by the i r indiscrimi­

nate use in agriculture.

86

EXPERIMENTAL

Two soil samples are used for the study of the mobility

of pesticides. The soils were dried, crushed and sieved through

100 mesh sieve.

1. Itwa silt loam (Aerie Ochraquelf) - Varanasi

2. Sakit sandy loam (Typic Natrustalf) - Etah

The physicochemical properties of these soils were deter­

mined as described in Chapter - I. The results are given in

Table - XIV.

The pesticides used for the study are organophosphorus and

chlorinated. The chemical name, structure and other properties are

given in Table - XV,

DETEfMINATION OF R^-VALUES BY SOIL THEN-LAYER CHROMATOGRAPHY(TLC);

Mobility of the selected pesticides in terms of their Re­

values in soils was determined by soil thin layer chromatography as

follows;

Apparatus; TLC applicator with adjustable thickness, uniform glass

plates of 20x4 cm size and glass t,anks 25x10 cm and a glass sprayer.

Preparation of solutions and soil samples

Solution of pesticides;

A 10% solutions of Thiometon, Malathion, Formothion and

Fluchloralin were prepared in ethanol.

87

Detector: A 0.59 AgNO, solution was prepared in a solvent

mixture containing acetone and water in the ratio of 3:1,

For the effect of organic matter? Two sets of experiments were

conducted to study the effect of soil organic matter and their

fractions i.e. humic acid and fulvic acid on the mobility of

pesticides.

In one set of experiments, two soil samples were used to

study the effect of organic matter by taking (1) as natural soil

containing organic matter and (2) the soil sample after removal

of organic matter by 309 2^2 ^^^^ there was no effervescence.

The results are reported in Table-XVI.

In other set of experiments, the organic matter was

extracted from the two soils namely Itwa silt loam and Sakit sandy

loam soils by the method of Desai and Ganguli (1979) and frac­

tionated into humic and fulvic acid; and then purified as follows:

Extraction of soil organic matter (30M): The soil samples were

slurried, sieved through 100 mesh sieve (BSS) and digested with

0.2N NaOH + 0,2N Na2C0, mixture (taking solid, water-alkali

mixture ratio as 1:10 wt/wt) for 6 hours at 80 C under continuous

stirring condition. It was then allowed to stand overnight. The

supernatant liquid was collected by siphoning and the residue was

again treated in the same way for several times for complete

extraction, Supernatants were pooled together and centrifuged at

5500 rpm and the residue rejected, A portion of the centrifugate

88

was purified by dialysis till the dialyzate was free of alkali.

It was again filtered through 0*22 mm membrane filter and kept

for electrodialysis.

Separation of humic acid (HA) and fulvic acid (FA)t The centri-

fuged extract was acidified with hydrochloric acid to pH-2 to

precipitate HA and then allowed to stand overnight. The yellow

coloured supernatant (FA) was siphoned off and collected. The

HA coagulated was centrifuged and the supernatant was mixed with

FA solution.

Purification of HA and FA; The HA was treated wi-tti ammonia

under slightly warm condition, allowed to stand overnight, centri­

fuged and the residue re^jected as it contains prefuse quantities

of Al and Fe, The HA was then precipitated from st4>ematant,

centrifuged and supernatant solution discarded. This process was

repeated several times till no residue was obtained on centrifU-

gation of ammonical supernatant. Again, the HA was dissolved in

ammonia and the solution was passed through 0*22 um membrane

filter and then purified by dialysis and electrodialysis.

In case of FA, it was tre£ited with ammonia, a bulky white-

brown precipitate of Al (OH)a> if appeared; was removed by fil-

tration (over Whatman filter paper no, 1), The pH of the filtrate

was brought back to 2 with HCl centrifuged and the supernatant made

ammonical again, allowed to stand overnight and then filtered

through membrane filter. The process was repeated several times

till no white precipitate was obtained upon the addition of ammonia.

89

The FA solution was concentrated by evaporation under an IR lasep

at 60 C, filtered through membrane filter and the filtrate was

brought back to pH 2 for dialysis and electrodialysis.

Dialysis and electrodialYsia; The solutions of HA and FA were

placed in central compartment of the electroanalysis cell and the

platinum electrode compartments were filled with doubly distilled

water and was changed intennittendly with stirring the HA and FA

solution in central compartment. It was continued till the water

in electrode compartment did not lahow the presence of chloride

ions. Again, the process was speeded ixp with the help of pro­

gressively increased d,c, voltage fr<Mn an initial 5 volts to 200

volts. The care was taken to replace the water from electrode

compartments. This process was continued till the conductance of

the water in the cathode compartm^it was equal to that of distill­

ed water.

The SOM, humic and fulvic acid thus prepared and purified

were stored in well cleaned glass reagent bottles. These com­

pounds (SOM, HA and FA) were then added to their respective soils

in known quantities. The amended soil samples were used to pre­

pare TLC plates for Rx.-values determination. The results are

reported in Table-XVII to XIX and Fig. 8.

For the effect of clay content; The clay mineral contents of the

soils (Itwa and Sakit) were separated as follows:

90

The so i l samples were a i r dr ied, broken ijqp in a morter using

rubber covered p e s t l e , and passed through 7 mesh sieve (BSS) to

ranove gravel por t ions . I t was then washed with d i s t i l l e d water

t o remove soluble s a l t s and t h a i t r ea ted with 30% H^Op solut ion t o

deccmpose s o i l organic matter ( t i l l no effervescence). Excess of

hydrogen peroxide was decomposed by gently warming the mixture

for few minutes. The cooled mixture was then covered with water and

s o i l dispersed with sodium oxalate solut ion (8 g m / l i t r e ) . The

mixture was shaken vigorously by an e l e c t r i c a l s t i r r e r for a few

hours . The col lo ida l suspension thus obtained was paissed through a

two layer sheet of Whatman f i l t e r paper no, 1 placed in the bowl

of In te rna t iona l Chemical Centrifug;e a t a speed of 3»500 rpm. The

res idue l e f t over in the bowl was again s t i r r e d with d i s t i l l e d

water and centrifuged as above. The process was repeated th ree or

four times to get suff ic ient clay suspensions which were a i r dried

and clay mineral was s tored.

The separated clay minerals were added to t h e i r respect ive

s o i l s which were used to prepare TL:^ p l a t e s for mobili ty determi­

na t ions . The r e s u l t s are reported in Table-XX and Fig, 9.

For the effect of pH: The effect of pH on the mobil i ty of

p e s t i c i d e s was studied using the s o i l samples a t various pH values

adjusted with 0.01N HNO or NaDH, These s o i l samples were coated

on the TLC p la tes for the mobility determinations. The r e s u l t s

a re given in Table-XXI,

91

For the effect of exchangeable cationsi The soil samples were

saturated with various cations i.e. H*, K*, Ca "*" and Hg "*" in the

sane manner as described in Chapter » I of the thesis* The

results are reported in Table-XXII,

For the effect of sesguioxides (AI2O, and FegO,)! The soil

plates were prepared by the addition of varying amount of AlpO,

and Fe^O,, The results are reported in Table-XXIII A XXIV and

Fig. 10.

Preparation of TLC plates: The glass plates (20x 4 cm) were

coated with soil or amended soil samples as described in Chapter-I

of this thesis.

Application of samples: A 0.006 ml of pesticide solution per

spot in single application was applied with a micropipette on the

base line at a height of 3 cm.

Develoiment of plates: The coated plates with soil sample were

developed in distilled water as described in Chapter I of this

thesis.

Drying and detection: The developed plates were air dried at room

temperature. Visualization of pesticides on the chromatogram was

made by spraying Ammonical AgNO, solution with the help of spray

bottles on exposure of these sprayed plates to sunlight for five

minutes. The Malathion, Thiometon and Fonnothion developed a yellow

colour spot which becomes bluish in about five minutes, while

92

Pluchloralin developed a distinct dark yellovr colour spot.

The colour so developed remain stable for about a week. The

mobility of pesticides in different soils was evaluated in terms

of R^-values as described in Chapter-I of this thesis,

RESULTS AND DISCUSSION

The mobility (R^-value) of ionic (Fluchloralin) and non

ionic (Formothion; Malathion and Thiometon) pesticides are report­

ed in Table-XVI, It shows that the pesticide mobility is greater

in sandy loam as compared to silt loam soil which has a large

available surface to bind the pesticide molecules. The order of

their mobilities in both soils ia Thiometon>Malathion>Formothion>

Fluchloralin, Considering the chemical structure of these pesti­

cides, it could be said that the ionic nature and the polarity of

the compound play a significant role in its movement through soil.

The least mobility of Fluchloral;Ln could be understood by its

relatively high affinity for the adsorption sites of soil colloids

as reported for ionic pesticides (Singhal and Kumar, 1976j Maqueda

et al,, 1983).

Among organophosphorus pesticides Thiometon has a reactive

sulphur atom attached with a hydrophobic ethyl group which inhi­

bits its interaction with soil colloid surfaces and hence shows a

highest mobility than the other two (i,e. Malathion and Formothion),

Whilst, in the case of Malathion and Formothion, both of which have

93

two carbonyl groups with o-atoms available for interactions with

soil colloids through hydrogen bonding and/or Vander Waal's

forces. The higher mobility of Malathion than Pormothion could be

due to a greater steric hinderance caused by two bulky ethyl groups

in the structure of former. The N-atom in Fonnothion may also pro­

vide another binding site for its interaction with soil colloide

and hence additional restriction slows down its mobility in soil,

Table-XVI shows that the mobility of all the pesticides

increases as the soil organic matter (SOM) is decomposed with H2O2

(30?6), It is obvious as the decomposition of SOM reduces the

binding sites in the soil colloid and hence increased the mobility.

This was again examined by adding SOM extracted from the same soil.

The resvats reveal (Table-XVII to XIX and Fig, 8) that on addition

of 0,5% SC*1, HA and FA to its respective soil, decreased the mobi­

lity of pesticides to about 0.2o to 0,35 R^ units. However, in the

case of Malathion, addition of 0,59 HA increased its mobility to

0.09 R^-units. It may be seen from the Table-XVlII that HA incre­

ased the malathion mobility, the corresponding decrease by FA goes

upto 0,58 and 0,61 R^-units in two soils and its average mobility

(with HA & FA) remains around the same as in the case of 0,5%

addition of SOM, However, some other factors such as mineralogical

properties and pH etc, may also contribute in restricting or en­

hancing the mobility of pesticides. Thus results could not be

explained quantitatively due to the complexity of the soil syat&n

unless the specific work is carried out on each aspect which is

beyond the scope of the sub;3ect of this chapter.

> H X

w K J

CO

H

o CO W H

I 04

Ok

o H

o

8 H

o •H •P O 03 U

«H

rrt

i4 i4 c\J

• I

H O

o

t4

a <uo

K CM* ft ••

o 0)

fci04-> < ^ u cd o a

i

o

CO

CO

in

o

c\j

VO

CVJ

in

in

CM

•H O

0 H +i H H W

cd > •P H

•H W Cd

S IH

a > v.-*

OvJ

H

4-00

m o

rn CNJ

in o

CTk

CM

00

CM

VD

0)

•H ^^ O

O

a II •P

•H O

•p

d o o •p

• H

Q)

•P •i •H H O cd

*

in

§ Si

QJ

o S o II II II

'r- CM H Ir-H

^

Cd o •H

94

> X

!3

I

o o

en

EH

O Oj

t ::5

^

;3 4J

H - H O <U

O

0)

0)

o o

o ft

O C)

•d

a o

w

O DH

a (u

f A r-) JCJ

o o 1 1

o o i 1 C\J CM

X X O C3

\ / <M 2 ; CM O . O y^ V

o / l \

Cij f-ij Ixi

-4-o

K^ "Z.

CJ rov r-

yu CM T -

o

K -TT* 1 K O

O :

X

r/5-

s 1

r o 1 1

i

1 -v^

1 CM

O ^ X

O ^^

CM

a.

g CM V -

X «X)

o

tA

^ o o o ^

x — ~ 4 C 0 = ( l i i CM

O K\

^-x

CM

M3 O

cn r-X

o r-

O

l A X

CM

o o V K^

- o

t n X

CM o 1

i CM

CM X o ^-^

1 CO

1

r/3r=:'^ 1 CM

o ro X

O «.—^

CM O

i n r-

p:: MD

o

S5

U o H .C O

H

rA

o-lA CM

•d •rH O a o o d -p •H TJ O

u Q Si ft w ^ 0 .

H >> g O

v^» 1

CM

k. CO

fn QJ

<U

^ - N

o fl •H

1 H >> ,!:! •P

a

o

o

o

o rA ro

- H 0) >>

•P,£5 52+* fl cu •H a o -R O XJ CD 3 1 -P CO O c\3 O " O

•P O - H

ft ill Cd ^ - P

CD 5: o a j ^ H fn O t > . C D ^ x;-p ft • P W CO Q) 0) Q

•M 1 ^ QCO ft

^ CM

-> •d o •H-H 0 4 3 cfl-P H

H >> O > > ^ • r i ^ - P O - P <U •H <o a ^ ^ • H +> 1 TJ •HCM 1

JH 1 O Q C O l ^ Xi 1 ft5^H fn W (U > , CU

g - P ^ - p 0 . (U (1) CD

o

H 05

O •P G)

a o

EH

98

TABLE - XVI

MOBILITY (R.^- VALUES) OF PESTICIDES THROUGH SOILS

Mobility (R^-values)

Itv/a s i l t loam Sakit sandy loam Pest ic ides

V/ith organic V/ithout With organic Without organic matter organic matter matter

matter

Fluchloral in 0.78 0.87

Formothion 0.80 0.84

Malathion 0.90 0.92

Thiometon 0.95 0.96

0.81

0.86

0.91

0.94

0.84

0.88

0.93

0.97

X

M CO

H

O

r3 Q H O H

o

> I

o

o

o

n . CO H

o

H O

rn

o O w

M O CO

^

EH

e

o

0)

>

«H a;

o Lr\

^ <f ^ cn

VO i n vo

K> l a

o i n

r -VD

-4-vo

^

o

o

o

o CM

O O

o

o o • • H

O c O ^ ^

o u

'xi o a

to 0!

•H O •H + i (/) Q)

o o o

o o o o

tn C\J IN

V£)

o o o o

vo CD

O O O

00

o

o CO

o

o o o o

o o o

vo vo o o

El H en

H

•H H

fii

o H .0,

o H

•H O

U H O C\3

f! o -p o a o •3

>H

i CO

EH

a ^ CO

• H H oJ SH O

o H

O

-P O

O

o

o J!

97

o

o-\ -d-

CM i n

o o

V -

t>-(X) i n

i n i n

m vo

00 vO

o o

•r-VO

• O

o vo

• o

CO vo

• o

'^ t>-

• o

CO

o

o ^-

« o

03 V£)

• O

m t>-

• o

^-co

« o

00 CO

• o

rn 0 -

• o

<f t^

• o

vo IN

« o

C\J CO

• o

\-00

• o

o CO

• o

r -CJ

• o

<l-cri

• o

o • p o 0 o

• H

EH

H H

EH

H

O

Q H O

o

O

H O en

I CO

H

05

w CL)

> I

o UA

O lA

i n LPV

m C7

lA v£»

lA i n

o ITv

O o

O KO

o

5 o

o •

o

o CM

o

o

o

o o

• o

o « o o n <u 'd I d

'd •H O aJ o •H

H - = 3 1 ^

w Q) 'd •H O •M -P W 0)

^

in

irv

CD

•S H H ^

H cn

<J ;^ EH H

0} U O H ^ O 13 H r i .

o o

o o o

CNJ

in

o

• • o o

o CO

o

O

o

O O O

O

o o o

o

m t>

00 IN

o

<y\ 00 • •

o o

in

o o

n 0

4J <U

a o •H

EH

^

a >H

g "5 CO

EH H

^ CO

o

in

•H H 05

o H

O

00 in

rn

o

+> o

o

^

o o o

o

m tn

CO t n

00 a\

cr> VD

CO i n

CM i n

CO o\

<f

<o o o o

t> 00

o

o !>-

• O

n I S

• o

CM cn • o

T~

CD •

o

T -

00 •

o

VD CO

• o

V -

CTi •

o

< ! •

a\ • o

a o •H Xi •P oJ H

a s

fi o + Q)

s o •d ^ EH

98

X H x:

m ^ ^

M

a

g

<D :i H > I

a:

o O

o -J-

(M lA ^

IN lA

<1-VD

O lA

r-<vD

00

m -4-VO

o

o o

o

o o •

o

CO -4-

LA CM

• O

O

o

MD (M K\ tA lA -:j-

• • • o o o

00

o

o o

o lA

o

00

o o CO

o o

lA

'H a O ^ ^

• XJ O - H f: o o a o

o X}^r^ (D > - d H T) :3 •A'i-i

w OJ -d •rl O •H P W cu

0-,

5^

H h4 H rO

-"$ H H

•H H oi ^ O H ,c: o :3 H HH

c o •H ^ •y ctf Q H o

fu

^ o •H Si -p 0} H OJ f-u

CO 00 ~J LA rA

O O O

O O

<1-lA

• O

lA '^

• O

00

o CO

o

:^

o

99 o o

o

O

o o

C\J VO

• O

rA IN

• o

00 lA

• O

VD C>-

• O

o r-

• o

CO VD

• O

lA VO

• O

cr\ lA

• o

fA CO

• o

CO VO

• o

CO 0 -

• o

C\J c

« o

CM 00

• o

•J-

m

o

c; o

-p

o :d EH

1 c/5

EH

§ CO

H as U O

d o H l i .

O •H X5

O

g o u^

a o

•H

•P cd H

. - 4

d O •P

O •H

EH

i

H

H H

O P

CO W Q H O H EH

a o

«H

W

w 0) :3 H OJ >

1

u a:

o •

ro

O • OJ

o

O

•4-

O

o o • o

CO tN

• o

o CO •

o

o <J\ •

o

tr\

as m

o

V—

00 •

o

\o 00 •

o

r -

cn • o

<f CTN

• O

O H O

O'd a-d

OJ •d •H O •H -P W 0)

0^

o

CM

CO

o

O

O O

< UD

• o

'C\J yo

• o

0^ VD

• o

VO c

• o

lA O CO

o o

o in

lA

lA VD * •

o o

o

O

3 EH ^ H CO

< •^ EH

•r4

•^ S o H

,E] O ^ H fn

C3

o

•P

o

o

o •H •P oJ H

o -p Q)

s o

EH

53

H

CO

•H

O H

o H

o

-P O

O Cr4

100

00 O LA VO

O O O

CO o lA VO

o o

lA

o •H

•P

H

CM v£)

• O

O

rA

o IN

• O

T"

t> «

o

CT\ t^

• O

0 -00

• o

CO VD

• o

o CV

• o

fA C^

• o

o 00

• o

o

a o

U CC\

o

H

O

a

o EH

[3 H O CO

'4 3

o CM

O

o

to

0)

>

CO

<H a:

o in

lA

CvJ

ft

w •r) •H o •H -P CO (U

s H CO

H

o o o

o o o

o

vD IN

(Ti 0- 3 ro

en lA (X)

o

^ u o H ^ o :3 H N

o •':1 A3 •p Q

g O

Ct

o •H

•P «J H «5

O -P 0) a o

EH

a •H H U

o H

O :i H

f1 o •H

-p o 0 U o

t4

cr»

o •H

•P ClJ

H cd

101

l A tN

C\J CO

CO (0

o o-

o CD

tN (D

LA CO

o o

<f t^

• o

c o

• o

l A CO

• o

r-(J\

• o

c\J CO

• o

c CO

• o

CM <Ti

• o

l A

a\ •

o

CTi

O O

o •

o

r~ CO

• o

CM 00

• o

- t CTv

• o

c cr>

• o

CO CO

• o

o OS

• o

vo en

• o

c <Ti

• o

CM C^

• o

LA C^

• o

VX> 00

• o

t— CJ\

• o

<!• CO

• o

LA CO

• o

CO CO

t

o

CM 0>

* o

l A VO

O C^

CM CO

CO 00

l A t^

O CO

<h CO

LA 00

o •p OJ

O

^

o CO

o M

o w

O X

w

o o w

ri3

w (U : H

> 1

'H Oi

H •H O

^ '4

H •ri O

^ K

H •M O

I

• H O

CO I

O

w

•a o •H -p w 0)

H •H O

"•O

CO tN

• o

o CO

• o

o a\

• o

lA (7\

• O

T -00

• o

VO CO

• o

r -(J\

• O

< ! •

cy\ •

o

r-o

• o

f

t^ • o

VT

00 • o

i n CO

• o

C -

c --4-CO

CO CO

o o o

o o CO

o o o o

00 CO CO a\

o o

CO ^

o 00

o

a H ^ H CO

<; *>• EH H

•^ U o a o :3 H rr

$3 o •H ^ o

^ o fe

o

H

o

a o

EH

O

o H

o

o

o

CO

o o o

en

102 CM <|-t ^ 00

o o o o

CO

o

00

o o o o

l>-c-

• o

r< CO

• o

r -00

• O

o t>-

• o

o •H -c: -p cd

H cd

1 ; i

0 -P 0) B o •H ^ EH

u

W

CO QJ :3 H cd > 1 «H

Di

O r<

• o

o rvj

o in

• o

o -4-

O

o

o

o o

0)

d

• p

O - H

<: o

CD

•H o

•rH

-P w ft.

o

w

Q

O

H

T- LA O ir\ ir\ c^

lA

00 irv

•H

O H O

(\J

o

O a u o

O

i n

^

i n

co

CNJ

• O

CO vO

• o

00 ^-

• o

s •

o

OJ

c * o

o CO

• o

• o

rn 00

• o

o cr\ • o

CM CO

• o

vD CO

• o

i n <i\

• o

tn

0) P4

o

VO

a o

•p

a H «i 2:

f3 0

+> 0 •H ^ H

v.^

W P

0

s Q (t H

H a u 0

Id 0 3 H li<

i n CO VO VO

o o

o

O <!•

CO O C ^ CO

• •

o o

o

-P O

o

CM

O

o

-p c\3

H

103

in 00 m in in in VO IS

• * • * 0 0 0 0

CO i n

* 0

CM VD

• 0

i n VO

• 0

CO IS

• 0

CM CO

VO

CO

o

o

O O

in

o

o 4J O a o .a

>

I

o LA

o

o

o

o

o CM

• o

o o

• o

• ^

0-•

o

IN c

• o

ro\ 00

• o

r-IN

• O

C--l >

• o

o CO

• o

-4-CO

• o

* o

o o

0) xi n a

xi

•< o

-d •H o •H • p

w 0)

O H

vO ir\ VD

• O

o t -•

o

OJ o • o

U5 o 00

o o

• • o o

Cvj CO

CO ro • •

o o

CO

o

VO CO

• o

r-

cn • o

<}• cr> • o

CM

VO CO

V O

o

00

o

V O CO

• H

O

o a H O

O CM

&H

O

o

o O •P o S o

•H w Q

^ O

^ Q ci H

H rf U O H ^ O :3 H ft^

c o :d -p o s (H O fe

CM

cr\

o

H

104 VO

O

ro VO

• o

00 VO

« o

CM C^

• o

^ f -

• o

<!• >X)

• o

o c>-

• o

irv t >

• o

CO t >

• o

o-vO

• o

tr\ t>

• o

f -t ^

• o

T— CD

• o

vO r>-• o

V -

CO •

o

<1-00

• o

t> co • o

-J-CJ>

o o

o p a o •ri

< o

<

o o ~

o CD

6

o IT)

6

o sf 6

o CM

6

2 < o _ I

>-Q Z <

<

Ci) •D •D

v_

£

O

E

iZ

c o oJ <;

C O

• J

Ci)

"D J C

in ^ ^

CL c

c o

-C - • - '

2

o >>

o C OJ

< X

o

•4-O

U

QJ

I CX5

o L L

c o x: - I - '

o E t _

o

OJ

o

u D

a^l^A^^d

o Lf)

o vi

o CO

O CN

O

o

o in

o <f

o n

O

rvi

o

n

o o

u

03

c Cs) •*-' c o U

>>

J 3 o

en D O

H

If)

O

o

•4—'

•

o E

•*->

c o If)

c — E >^

• D Cs)

• D TJ 0)

O

- • - '

M—

LU

cn

O

(/)

o

E 03 o

C 03 (/)

-•-•

j i OJ

CO

• D

c 03

E 0)

o • • - '

U) CO

•»-'

c

o JZ

LI

• v ^

• D

C 03

C

o JZ

o E v_

o

X

c o x: 03

03

^

o ^-^

c o

£ o JZ 1 -""" <I

LL

2>niEA-^y

ITWA SILT LOAM

0-4 0-6 0 0-2

Metal oxidB adde<) (7o) 0-4 0-6

Fig. 10. Effect of metal oxide (AI2O3 & FC2O3 ) on the mobility

of pesticidei; (•) F luchloro l in^ (x ) Formothion,

(o) Molathion, (A) Thiometon.

105

Table-XX and Fig, 9 show that on addition of clay minerals

to respective soil decreases the pesticide mobility to about 17

to 25 R^-units in Itwa silt loam and 29 to 34 Rj^units in Sakit

sandy loam soil. This decrease may also be attributed to increased

binding sites in the soil colloids due to the addition of clay

fractions. The greater reduction in pesticide mobility in Sakit

sandy loam than in Itwa silt loam could be explained on the basis

of the nature of clay mineral added. As the separated clay from

Sakit sandy loam soil contains chlorite mineral with mica and has

a higher CEC values in ccmparison to the other clay separated

(Kaolinite with mica) from Itwa silt loam. The addition of clay in

the former soil increased its CEXJ values from 123 meq Kg to 141

meq Kg soil in comparison to the later soil which becomes 117

-1 -1

meq Kg from 116 meq Kg by adding 5% soil clays. The pesticide

mobility order ronained the same in both the cases showing the

importance of their reactivity in soil colloids,

Table-XXI indicates that the highest pesticide mobility

was found around the neutral pH and decreased in both the acid

as well as alkailine pH range. It could be due to a fixation of

H ions over adsorption sites which may bind the pesticide mole­

cules through hydrogoi bonding to restrict the mobility in acid

soils. Whilst, in the case of alkaline medium, the soil organic

matter gets solublized and also the cations on the exchange sites

of mineral surfaces gets hydrolyzed. These hydrolyzed cations

presumably adsorb the pesticide molecules through hydrogen bonding.

The possible interaction could be vritten. as follows:

In acid medium

adsorption ^ ^ ^ ^ ^^ sixes

pesticide molecule

In alkaline medium

si?e?^^''''^*-°" * °-^

pesticide molecule

106

adsorption sites ^ H * . . . 0 -

^J^^^*^^°^!1*.0H . . . 0-X

Table-XXII shows that the pesticide mobility in cation

saturated soi ls follows the orderj Unamended soi l>H-30i l>

Ca-soil>Mg-soil>K-soil , in both the soi ls under study. Various

authors (Singhal et a l . , 1978| Khan and Bansal, 1980) have repor­

ted that the pesticide molecules adsorbed onto the cation satura­

ted soi l surface through the cations and hence hydrated cation

s ize could be a important factor in deciding the pesticide adsorp­

t ion order. The hydrated size of H i s largest and K being

smallest (Table-OCXII), Thus, the greater hydration of H -ions

in H-saturated soil than other ions, prevents the interaction

b-etween pesticide and soi l colloids. However, the role of pH of

the H-saturated soi l which i s decreased from 10,5 to 7,9 and 6,6

to 3,2 in Sakit sandy loam soi l and Itwa s i l t loam soil respective­

ly , could not be ruled out.

107

However, in the case of Ca- and Mg- soil, the lower value

of ionic index (Zi /r) for Ca (4.04) than Mg •*" (6,15) seems to

be a reason for their lesser interaction (Nieboer and Richardson,

1980) with pesticide molecules and hence a higher pesticide mobility

was observed in Ca- soil than Mg- soil.

Table XXIII & XXIV and Figure 10 show that the mobility of

pesticides decrease with the addition of Al^O, and FopO, in both

the soils. It may be explained on the basis of increased binding

sites due to the interactions of precipitated Al and Fe hydroxide

(Khan and Khan, 1986) species.

108

REFERENCES

BAILEY, G.W. and WHITE, J.L.; J. Agric, Food Chem., 12, 324 (1964).

DESAI, M.V.M. and GANGULY, A,K,; J, Indian Chem. Soc., 56, 1167 (1979).

DESHMUKH, S.D., AKHARE, M.D. and BORLE, M.N.; Indian J, Plant Prot., 7, 66 (1980).

GHOS, M.R.; Pesticides, 13, 9 (1979).

JACKSON, M.L.; Soil chemical analysis. Englewood Cliffs, NJ, Prentice Hall (1958),

KHAN, S.U. and BANSAL, V.; J, Colloid and Interface Sci,, 78, 554 (1980).

KHAN, S.U., KHAN, N.N. and IQBAL, N.; J, Indian Soc. Soil Sci., 33, 779 (1985).

KHAN, S.U. and KHAN, N.N.; Soil Sci,, 142, 214 (1986).

KURLEKAR, V.G. and KHUSPE, V.S.; Pesticides, 18, 11 (1984).

MAQUEDA, C , PEREZRODRIGUEZ, J.L., KARTIN, F., and HOSIN, H.C; Soil Sci., 136, 75 (1983).

MORTLAND, M.M.; Adv. Agron., 22, 75 (1970).

NEARPASS, D.C.; Soil Sc i . Soc. Am. P r o c , 35, 64 (1971).

NIEBOER, E, and RICHARDSON, H.S. ; Environ. Po l lu t , (Ser, B), 1,3 (1980).

RAGHAVAIAH, C.V., BABU, M.S. and RAO, M.S.; Pes t i c ides , 14, 32 (1980).

SINGHAL, J . P . and BANSAL, V.; Soil S c i . , 126, 36o (1978),

SINGHAL, J . P . , KHAN, S.U. and BANSAL, O.P.; Aust. J . Chem., 31 , 2151 (1978).

109

SINGHAL, J . P . , and KUMAR, D.; So i l S c i , , 121, 156 (1976).

THIMMAIAH, G. and THIPPESWAMY, C ; Pes t i c ides , 14, 7. (1980).

CHAPTER - III

ADSORPTION OF Cu "*'. Pb " AND Zn '*' ON

Ga- SATURATED ILLITE

no

INTRODUCTION

Accumulation of certain heavy metals such 2+ 2+ 2+ - continuous

as Cu , Pb and Zn in soil, due to 'application of chemical

fertilizers and sewage sludge (Anderson and Nilsson, 1972; Dutta

and Mookheroee, 1980) is posing serious concern to soil pollution.

Several attempts have been made to understand the basic chemistry

of adsorption and desorption processes of these metals over soil

colloids in recent years (Joshi and Shanna, 1986; Chatterjee and

Mandel, 1985) which provides informations on their availability

to plants. Copper (II) and Zinc (II) are considered as soil nutri­

ents and neeeded for healthy crops growth (Joshi et al., 1981,1982)

while lead (II) is toxic metal (Walker et al., 1977j Nakos, 1979)

and not required for plant growth. Adsorption and interaction of

these metals over soil colloids is found to depend largely on

several factors such as nature of saturated cations (Dhillon et al, and 'fada

1984; Abd Elfattah,^1981), soil pH (Maguire et al., 1981; Robert

et al,, 1983), type and extent of clay minerals, soil organic matter

(SOM) contents etc, (Petruzzelli et al,, 1981; Jahiruddin et al,,

1985).

The present work deals with the adsorption of Cu "*", Pb "*"

and Zn through adsorption isotherms, Freundlich equation constants

and thermodynamic parameters such as AG, As and A H so as to get

some valuable information on the degree of their interaction over

illite surfaces saturated with Ca ions which is most common in

calcareous soils.

I l l

EXPERIMENTAL

The clay mineral used in these investigations was illite,

obtained from Ward's Natural Scien,ce Establishment Inc., Rochester

(USA). It was broken up in a mortar using a rubber covered pestle.

A <2 yuni fraction was obtained by dispersion in distilled water and

subsequently passing it through the sheets of Whatman filter paper

No. 1 fitted, in the bowl of 'International Chemical Centrifuge'

at a speed at 3500 rpm. The organic impurities were decomposed by

30% ^2^2 ^^'^ ^^® •'•• ^^ suspended in distilled water for further

use.

PREPARATION OF SODIUM SATURATED ILUTS

The clay suspension was treated with 2N sodi\m chloride

solution several times. The mixture was then shaken each time for

about half an hour and allowed to settle down. The supernatant salt

solution was removed from the clay by decantion. The clay is washed

with distilled water till it was free from Cl~ ions (negative AgNO,

test) and the conductivity of the suspension was almost equal to

that of distilled water. The clay suspension was then stored in

bottles for use.

PREPARATION OF Ca- SATURATED ILLITES

The Ca- illite was prepared from Na- illite by treating it

with 2N calcium chloride solution in the same manner as described

112

above fo r t h e p r e p a r a t i o n of Na- i l l i t e . The C a - s a t u r a t e d i l l i t e

sample was then s t o r ed i n s toppered g l a s s b o t t l e s fo r u s e ,

DETERMINATION OF CONCSI TRATION OF TEE. Ca- ILLITE

The concen t r a t i on of t h e Ca- i l l i t e was determined by evapo­

r a t i n g 10 ml of t h e suspension i n p e t r i d i s h of known weight and

dry ing t h e r e s i d u e a t 105 C and f inia l ly determining t h e weight of

r e s i d u e l e f t . The concen t r a t i on of Ca- i l l i t e was found 22.8 g/

l i t r e .

DETERMINATION OF THE CATION EXCHANGE CAPACITY OF THE Ca- ILLITE

The c a t i o n exchange capac i ty (CEC) of t h e Ca- s a t u r a t e d

i l l i t e was determined by t h e ammonium a c e t a t e method (Jackson, 1958)

as desc r ibed i n Chapter - I of t h i s t h e s i s . The c a t i o n exchange capa­

c i t y fo r calcium i l l i t e was found t o be 31 .5 meq/lOO g c l a y ,

ADSORPTION EXPERIMENT

The adsorp t ion experiments of Cu "*", Pb "*" and Zn "*" were

conducted by t ak ing 5 ml of t h e Ca- i l l i t e suspensions i n a l a r g e

number of g l a s s s toppered t ubes and adding varying amounts of 0.01N

of Cu (NO,)p, Pb(N0,)2 °^ 2ii(N0^)2 s o l u t i o n i n s e p a r a t e s e t s and

a d j u s t i n g t h e mixture t o a cons tan t volume (25 ml) wi th d i s t i l l e d

wa te r and shaking t h e s e tubes a t 30 C i n t h e f i r s t s e t of e x p e r i ­

ments and a t 60 C i n t h e second s e t for 12 hours i n each c a s e .

m The suspensions v/ere then cen t r i fuged and t h e r e s i d u a l Cu, Pb and

Zn ions were es t imated by s t andard EDTA s o l u t i o n ( R e i l l e y e t a l , ,

1959) . The d i f f e r ence between metal ion concen t r a t i on added minus

t h e amount of metal ions i n superna tan t l i q u i d s gave t h e amount

of metal adsorbed by t h e c l a y . The de te rmina t ion of Cu "*", Pb "*"

and Zn '*' a re made as fol lows and r e s u l t s a r e given i n Table XXV t o

XXVII and F i g . 11 .

DETERMINATION OF COPPER (Cu "*")

The amount of copper (Cu ) was es t imated i n equ i l ib r ium

s o l u t i o n by EDTA t i t r a t i o n method us ing PAN as i n d i c a t o r .

REAGENTS REQUIRED; The chemicals used fo r t h i s experiment were

of BDH a n a l y t i c a l grade and t h e i r s o l u t i o n a r e p repared as fo l lows:

S tandard EDTA s o l u t i o n : A 0.01N EDTA s o l u t i o n was prepared i n

d i s t i l l e d wate r .

PAN / ~ 1 - ( 2 - P y r i d y l a z o ) - 2 - N a p t l : i o i y s o l u t i o n : A 0,1% s o l u t i o n of

PAN was p repa red in methyl a l c o h o l .

Buf fe r s o l u t i o n (pH 4 ) : Buffer s o l u t i o n of pH 4 was p repared by

mixing 180 ml of N/5 sodium a c e t a t e and 820 ml of N/5 a c e t i c ac id

s o l u t i o n .

Procedure; A 5 ml of superna tan t l i q u i d v/as talcen in a b r e a k e r ,

t r e a t e d wi th 5 ml bu f f e r of pH 4 and t h r e e drops of PAN i n d i c a t o r .

114

The contents were then titrated with standard EDTA solution. From the

values EDTA solution used up minus the blank reading, the amount of

Cu "''adsiartied by Ca- illite was calculaited.

DETSRI4INATI0N OF LEAD (Pb " )

The amount of lead (Pb "*") was also estimated in equilibrium

solution by EDTA titration method using xylenol orange as an indi­

cator as follows:

Standard EDTA solution; A 0.01N EDTA solution was prepared in

distilled water and standardized with standard CaClp solution using

eriochrome black 'T' as indicator and buffer solution of pH 10,

Buffer solution (pH 5.5); A 41,0 g sodium acetate trihydrate was

dissolved in distilled water and 30 ml of glacial acetic acid was

added to it. The volume was made to 500 ml with distilled water.

Indicator solution; A 0.1 g of xylenol oriange indicator was weighed

and dissolved in 10 ml of methyl alcohol.

Procedure; A 5 ml portion of supernatant liquid was taken in a

beaker and 10 ml of buffer solution (pH 5.5} was added to it. The

mixture was wanned to 50 C, 2 drops of xylenol orange indicator is

added and titrated with standard EDTA solution to a light yellow

end point. From the volume of EDTA used minus the readings of re-

agent blank, the amount of Pb "*" adsorbed by Ca- illite was calculated.

115

DETERMINATION OF ZINC (Zn^"^)

The amount of zinc (Zn ; was estimated in equilibrium

solu t ion by EDTA t i t r a t i o n using ammonium fluoride solut ion as mask­

ing agent for calcium (Reil ley et a l , , 1959) and eriochrome black

•T' as ind ica to r .

REAGENTS RaaUIREDt The chemical used for t h i s are prepared as

follows:

Standard EDTA solut ion: A 0.01N EDTA solut ion was prepared in

d i s t i l l e d water.

Buffer solut ion (pH 10); Dissolve 54 g of ammonium chloride in

200 ml of water then add 350 ml of 25% ammonium hydroxide and d i l u t e

t o one l i t r e in d i s t i l l e d water.

Procedure: A 5 ml port ion of supernatant l iquid was taken in a

beaker, add 5 ml of Ammonium fluoride solut ion and then t r e a t e d with

5 ml of a buffer pH 10 and three drops of eriochrome black 'T ' i n d i ­

ca to r . The contents were then t i t r a t e d with standard EDTA solut ion

t o a blue end point . From the values of EDTA solut ion used minus

t he blank reading, the amount of Zn adsorbed by Ca- i l l i t e was

ca lcu la ted .

lis

RESULTS AND DISCUSSION

The results of adsorption of Cu "*", Pb "*" and Zn "*" experiments

at 30°C and 6o°C over Ca- illite are reported in Tables-XXV to

XXVII and Fig, 11. It is observed that the adsorbed amount of

these metals en to the illite surface decreases with the rise in

temperature. It has been a general observation in adsorption pro­

cess (Bartell et al., 1951) that the kinetic energy of the inter­

acting ions increases and therefore the electrostatic attraction of

these species decreases which results a decrease in their adsorp­

tion with the rise in temperature.

The adsorption isotherms (Fig, 11) show that the adsorption

of the heavy metal ions over Ca- saturated illite follow the order

Cu>Pb>Zn at 30° and 60°C. This sequence is indicative of the

retention affinity of the metal ions or their calcium replacing

power over the exchangeable sites of the illite surfaces. Similar

view has also been observed by Forbes et al. (1976) working on

geothite.

The adsorption data conformed to Freundlich equation. The

relative binding stren,-,th between clay siirface and the cations,

could be obtained easily by Freundlich equation constants (Table-

XXVIII). Freundlich adsorption equation may be written as:

/ „ Vn x/m = KC

or In x/m = InK + Vn InC

117

where x/jjj g the amount adsorbed by mass 'm' of the adsorbent,

K andVn are constants and depend upon the nature of the adsorbent,

adsorbate and temperature and C is the equilibrixim concentration

(/ig/ml) in solution. A plot of In x/j against InC is shov/n in

Fig, 12, The value of K which is a measure of adsorption capacity

was calculated by extra polating the curve to zero equilibrium con­

centration (C = 0). The value of V n which is a measure of adsorp­

tion intensity was determined from the slope of the Freundlich

adsorption isotherms (Fig, 12), The calculated values of these

constants are reported in the Table-XXVIII, The adsorption capacity

(K) of these ions follows the same order Cu ''•>Pb "*">Zn "*". The

values are found to decrease with the increase in temperature which

confirm our earlier deduction for the adsorption order and tempera­

ture effect. However the values of 1/n shows the reverse order of

their adsorption capacity (K), These values indicate that there is

an inverse relationship between adsorbent capacity and intensity

of adsorption.

The thennodynamic parameters such as equilibrium constant

(KQ) , ree energy {C^Q ), enthalpy (AH ) and entropy (AS ) asso­

ciated with the metal ions adsorption on Ca- illite surface at 30

and 60 C were calculated according to .

the following relationship:

TABLE - XXV

118

ADSORPTION OF Cu^"^ ON Ca- I LUTE AT 30°C AND 60°C.

Concen t ra t ion of c l ay suspension =

Volume of

S t r e n g t h <

c l ay suspension t aken =

Df Cu(N0^)2 sol^"^^®"

T o t a l volume of mixture

Volume of t i t r a t e d

Volume of 0.01N Cu(N0^)2 added

(ml)

At ^O^Z

0 . 5 1.0 2 . 0 3 .0 4 . 0 5.0 7 . 0

10.0

At 60°C

0 . 5 1.0 2 . 0 3 . 0 4 . 0 5.0 7 .0

10.0

=

=

superna tan t s o l u t i o n =

Volume of 0.01N EDTA used

(ml)

0 .04 0.09 0.18 0.33 0.42 0.57 0 .88 1.32

0 .05 0.10 0.19 0 .35 0.45 0.62 0.93 1.39

Amount of

22 .8 g / 1

5 ml

0.01 N

25 ml

5 ml

Cu2+ Amount of Cu^ in equ i l ib r ium adsorbed s o l u t i o n

(meq/1)

0 .016 0 .036 0 .072 0.132 0 .168 0 .228 0.352 0 .528

0 .020 0 .040 0.076 0 .140 0 .180 0 .248 0 .372 0.556

(i oieq/lOOg c l ay )

2 .63 4.82 9 .65

11.84 16.66 18.86 22.80 29.82

2 .19 4.39 9.21

10.96 15.35 16.66 20.61 26.75

119

TABLE - XXVI

ADSORPTION OF Pb^"^ ON Ca- ILLITE AT 30^C AND 60^C.

Concen t ra t ion of c lay suspensior:

Volume of c l ay suspension t aken

S t r e n g t h of

T o t a l volume

Pb(N0,)2 sol^'^^io^

; of mixture

Voliome of supen ia tan t s o l u t i o n t i t r a t e d

Volume of 0.01N Pb(N0,)2 added

(ml)

At 30°C

0 .5 1.0 2 . 0 3 . 0 4 .0 5 .0 7 . 0

10 .0

At 60°C

0 . 5 1.0 2 . 0 3 . 0 4 .0 3,0 7 . 0

10.0

Volume of 0.01N EDTA used

(ml)

0 .05 0.11 0.19 0.35 0.47 0.63 0.97 1.44

0.06 0.13 0.19 0.37 0 .49 0.63 0.99 1.53

L = 2 2

=

= 0.

=

=

Amount of i n , e q u i l i t s o l u t i o n

(meq/1)

0.020 0 .044 0.076 0.140 0.188 0.252 0.388 0.576

0.024 0.052 0.076 0.1^8 0.196 0.252 0.396 0.612

U8 g/ ]

5 ml 01 N

25 ml

5 ml

Pb^* irium

Amount of Pb "*" adsorbed (raeq/ 100g c l ay )

2 .19 3 .95 9.21

10,96 14.47 16.22 18.86 24.56

1.75 3.07 9.21

10.09 13.59 16,22 17.98 20.61

120

TABLE - XXVII

ADSORPTION OF Zn "*" ON Ca- ILUTE AT 30°C AI^ 6Q°C

Concent ra t ion of c lay suspension =

Volume of c lay suspension t aken =

S t r e n g t h of Zn(NO,)p s o l u t i o n

T o t a l volume of mixture

Volume of t i t r a t e d

Volume of 0.01N Zn(N0^)2 added

(ml)

At 30°C

0 . 5 1.0 2 .0 3 .0 4 . 0 5 .0 7 .0

10 .0

At 60°C

0 . 5 1.0 2 . 0 3 .0 4 . 0 5 .0 7 .0

10 .0

=

superna tan t s o l u t i o n =

Volume of 0.01N EDTA used

(ml)

0.06 0.13 0 .20 0.38 0.52 0 .68 1.02 1.54

0.06 0.13 0.21 0.39 0.53 0.71 1.07 1.57

Amount of

22 .8 6 /1 5 ml

0.01 N

25 ml

5 ml

•7 2 + Zn i n equ i l ib r ium

s o l u t i o n (meq/1)

0.024 0.052 0.080 0.152 0.208 0.272 0.408 0.616

0.024 0.052 0.084 0.156 0.212 0.284 0.428 0,628

Amount of Zn "*" adsorbed (me jq/100g c l a y )

1.75 3.07 8.77 9 .65

12.28 14.03 16.66 20.17

1.75 3.07 8.33 9.21

11.84 12.72 14.47 18.86

ni

TABLE - XXVIII

2+ _ 2 + 2. FREUNDLICH CONSTANTS FOR Cu " . Pb " AI^ Zn'""*' ADSORPTION

ON Ca- ILLITE AT 3Q°C AND 60°C,

Meta l ions Temperature Freundl ich Cons tan ts

(°K) • K V n

Copper

Lead

Zinc

303 333

303 333

303 153

50.5 46.3

41.8 40.8

35.8 30.9

0.69 0.73

0.71 0.78

0.75 0.79

22

TABLE - XXIX

THERMODYNAMIC PARAMETERS FOR CU ' , Pb^"^ AND TJ?"^ ON Ca- ILLITE SURFACE

Thermodynamic Parameters M e t a l T emp er at ur e

/0v^ ? T ^ ^ " AG^ AH° AS° ( K) brium

constants (KQ) (Calmole"'') (Calmole"^ )(Caldeg"''mole"''

Copper 335 24.0 -2103 "^99 4^2

X ^^o ^ u ^ '^-^. • - 1 0 : ? ^ 77-7 3 . 7

Zinc ^^^ ^)i'7, -^^n:; -74 5.8

303 333

303 333

303 333

26.6 24.0

23.1 20,6

20.6 20.4

-1977 -2103

-1892 -2002

-1824 -1997

0-40 0-50 0-60 0-65 Equilibrium concentration (nneq/l)

2+ 7+ 7+ FIG.11 Adsorption isothernns of Cu, Pb and Zn

on Ca-i l l i te .

W/x Ul

o

I TJ

U c o

+ N c

M • D C 03

+ n Q_

^ -

o

o in

E i_ Ci)

SI o I/)

c o

o •D *TJ

H u

c D

cn

iZ

12 0

A G ° = - RTlnKo

m ^02 I inKo = -AH°/R ( " Y - - - f - )

and AS° = ( A H ° - A G ° ) / T

(where a l l the symbols have t h e i r usual meanings).

The calculated values for K Q , A G ^ , A H and AS^ are reported in

Table-XXIX.

The negative free energy change ( AG°) (Table-XXIX) in a l l

the case ind ica tes t h a t the adsorption of metal ions over Ca--2+ ^^ 2-1

i l l i t e surface follows the order: Cu > Pb ^ Zn, The free energy

change which i s a measure of the driving force for a react ion to

occur, decreases with r i s e in temperature in a l l the cases show

t h a t the adsorption decreases at higher temperature. The exchange

r eac t ions were therefore spontaneous and there was a higher p re fe -

rence of the heavy metal ions over i l l i t e surfaces than for Ca 4+ At 4+ j-t

ion . The data confirms the s e l ec t i v i t y order C u > Pb >• Zn > C a over i l l i t e surface.

The negative values of standard enthalpy change ( A H ) in

a l l cases during the exchange react ion show tha t the react ion i s

exothermic and the heavy metal ions are more t i g h t l y bound on the

exchange s i t e s of the i l l i t e surfaces as compared to the calcium

ions and the adsorption decreases as the temperature increases .

124

The above conclusions are supported "by entropy (AS ) gain

during the Cu , Pb and Zn "*" exchange with Ca- i l l i t e . The +ve

values of the entropy change indicate tha t the system becomes more

disordered in the adsorption process of Cu "*", Pb "*" and Zn " over

Ca- i l l i t e . This i s possibly due to the breaking of the s t ruc ture

of the adsorbed water layer with a concomitant change in the hydra­

t i o n s ta tus of the cation t ransfer red from clay solut ion phase

(Van Bladel and Menzel, 1969).

m REFERENCES

AbD-ELFATTAH, A. and WADA, K.: J , Soi l S c i . , 32(2), 271 (1981).

ANDERSSON, A.^and NILSSON, K.O.; Ambio, 1, 176 (1972).

BARTELL, F.E. , THDMAS, T.L. and YING, Pu; J . Phy, Colloid Chem., 55, 1456 (1951). .

BIGGAR, J.W. and CHEUNG, M.W,; So i l Sci , Soc. Am. Proc . , 37, 863 (1973).

CHATTERJEE, A.K. and MANDEL, L.N.; J , Indian Soc. So i l S c i . , 33(3) , 669 (1985).

DHELLON, S.K. and DHILUON, K.S.; J . Indian Soc, Soi l S c i . , 32(2), 250 (1984),

DUTTA, I . and MOOKHERJEE, A.; Indian Environ, Health, 22, 220 (1980),

FORBES, E.A., POSNER, A.H. and QUIRK, J . P . ; J , So i l S c i , , 27(2), 154 (1976),

JACKSON, M.L.; 'So i l Chemical Analys is ' , Prent ice-Hal l , Englewood C l i f f s . , N.J. (1958).

JAHERUDDIN, M., 'IIVESEY, N.T, and CRESSER, M.S.; Commun, Soi l Sci , Plant Anal . ,16(8) , 909 (1985).

JOSHI, D.C., DHIR, R.P. and GUPTA, B .S . ; J . Indian Soc. So i l S c i . , 29, te (1981).

JOSHL, D.C., DHIR, R.P. and GUFTA, B.S . ; J . Indian Soc. Soi l S c i . , 30, 547 (1982).

JOSHI, D.C. and SHARWA, B.K.; J . Indian Soc, Soi l S c i . , 34, 257 (1986).

MAGUIRE, M., SALVEK, J . , VIMPANY, I . , HIGGINSON. F.R. and PICKERING, W.F.; Aust, J , So i l Res , , 19(3), 217 (1981).

120

NAKOS, G.; Plant and So i l , 53, 427 (1979).

PETRUZZELLI, G., GUIDI, G. and UJBRANO, L.; Heavy Met. Environ., I n t . Conf. 3rd, 866 (1981).

REILLEY, C.N., SCmiD, R.W. and SADEK, F .S . ; J . Chem. Educ., 36, 555" (1959).

ROBERT, D. HARTER; Soi l Sc i . Soc. Am. J . , 47, 47 (1983).

VAN-BLADEL, R. and MUNZEL, R.; Proc. In te rn . Clay Conf., Tokyo, 619 (1969).

WALKER, W.M., MILLER, J .E . and HASSETT, J . J . ; So i l S c i . , 124, 145 (1977).

CHAPTER - I V

STUDIES ON THE ADSORPHON OF METHYL. 2-aENZIMIDA20LE

CARBAMATE (MBC) WITH CLAYS AS AFFECTED

BY VARIOUS SOIL PARAMETERS

127

INTRODUCTION

Methyl, 2-Benzimidazole Carbamate (MBC) is a systemic

fungicide used to control a wide spectrum of fungal diseases

(Ram and Vir, 1984; Sandhu and Gill, 1982). It has been shown

that it can interact with soil colloids because of its persis­

tence in soil with a half life period of several months

(Baude et al,, 1974), Adsorption studies on MBC have been carried

out by various workers (Aharonson and Kafkafi, 1975; Khan and

Khan, 1986; Khan et al,, 1987) to show that the nature of its

interaction with clays and soils differ significantly depending

upon the soil constituent, soil properties and pH etc. However,

studies on its adsorption over various type of clays as influenced

by some soil parameters such as soil organic matter, sesquioxide

and soil pH have been lacking in literature.

The present chapter reports the influence of the nature

of clay minerals, soil organic matter, sand, free Al- and Fe-oxides

and soil pH on the adsorption of MBC which might be useful to

understanding its behaviour in various types of soils containing

these clays.

EXPERIMENTAL

The clay minerals used in these investigations were

montmorillonite, synthetic montmorillonite, illite, kaolinite and

128

dickite which were obtained from Ward's Natural science establish­

ment, Rochester, NY (USA ). A ^ 2/um fraction of the clays were

separated by dispersion and centrifugation, taking care to remove

most of the sand and dark coloured silt. The organic matter was

decomposed by treatment with 30% HpOp and then the suspensions were

converted into Na- clays as follows:

PREPARATION OF SODIUM SATURATED CLAYS

Na- clays were prepared by the same method as given in

Chapter- III of this thesis.

DETERMINATION OF CATION EXCHANGE CAPACITY

The CEC values of Na- form of clays were determined by

ammonium acetate method (Jackson, 1958) as described in Chapter-I

of this thesis. The CEC values for Na- forms of montmorillonite,

synthetic montmorillonite, kaolinite and dickite clays were found

to be 118.5, 110.0, 38.80, 12.5, 10.8 meq per 100 g clay respec­

tively,

DETERMINATION OF SURFACE AREA

Surface area of clay samples were determined by Hendricks

and Dyal's method (1950). For this, weighed samples of Na- clays

were taken in small aluminium boxes of known weights. The samples

were sprayed evenly over the bottom of the boxes. The boxes,

12!}

without lid were placed in a dessicator over 250 g of PpOc. The

samples were then dried to a constant weight. They were then

wetted with ethylene glycol added from a pipette dropwise and

warming. The samples were then placed in a dessicator and allowed

to stand at room temperature (30 C). Weights of the samples were

recorded after every sixteen hours interval and drying continued

till two successive weights agreed upto tenth of a milligram.

Surface area was then calculated from the equation:

Wg A =

Ws X 0.00031

2 where A » surface area in m /g; Wg = weight in grams of

glycol retained by samples, Ws = weight in grams of the samples

on PpO^ dried basis and 0.00031 is the Dyal Hendricks value for 2

the grams of glycol required to form a monolayer on one m of

surface area. The surface area of Na- forms of montmorillonite,

synthetic montmorillonite, illite, kaolinite, and dickite clays

2

were found to be 808,5, 710,5, 114,0, 35.5 and 30.5 m /g respec­

tively.

DETERMINATION OF MBC

Methyl, 2-Benzimidazole carbamate (MBC) concentration in

supernatant liquid was determined by UV spectrophotometer against

reagent blank at 280 nm wavelength (Chiba, 1977). The standard

curve for MBC is shown in Fig, 13,

130

ADSORPTION EXPERIMENTS

In a duplicate set of experiments, 0,5 g of each clay

minerals were taken into 500 ml conical flask and varying amounts

of MBC (0 to 1000/ig) in 0.01M NaCl solution were added to it.

The total voliime of the suspension made to 250 ml with distilled

water. The suspensions were equilibrated in a electric driven

shaker and the temperature was made constant at 30 + 1 C, It was

centrifuged after 8 hours (equilibrium time of MBC adsorption)

for 20 mts at 10,000 rpm. The concentration of MBC in supernatant

liquid was determined as described earlier. The amounts of MBC

adsorbed over clay minerals were calculated from the amount of MBC

added minus the amount of MBC remaining in the supernatant solution.

The results are given in Table-XXX to XXXIY and Fig. 14.

Effect of Soil Organic Matter;

To study the effect of soil organic matter on the adsorption

of MBC, two sets of experiments were carried out with a low

(aoO^g MBC/g clay) and high (2000/Ug MBC/g clay) amount of added

MBC, The soil organic matter was extracted from a peat soil by the

method of Desai and Ganguli (1979) and added to the above experi­

ments in varying amounts. The incubation, centrifugation and ad­

sorption was carried out in the same manner as in the case of

adsorption experiments. The results are shown in Table-XXXVI and

XXXVII and Fig. 16(a).

131

Effect of Sand content;

For studying the effect of sand on the adsorption of

FiBC, varying amount of sand with a particle size ,85 nun were

added to the adsorption reaction vessel. The method for the

adsorption of MBC remained the same as above. The results are

recorded in Table-XXXVIII and XXXIX and Fig. 16(b).

Effect of Free Al20^ and Fe20,;

The effect of free Al- and Fe-oxides on the adsorption of

MBC was studied by adding varying amount of AlpO, and 620^ to

the adsorption reaction vessel. The results are reported in

Table- XL and XLI and Fig. 16(c).

Effect of Suspension pH;

The effect of suspension pH on the adsorption of KBC was

studied by varying the suspension pH to 3,6,9 and 12 with the

help of 0.01N HNO, or NaDH, The experiments were carried out in

the same manner as described above. The results are reported in

Table-XUIandXLLII and Fig. 16(d).

RESULTS AND DISCUSSION

An examination of adsorption isotherms (Fig, 14) shows that

the adsorption of MBC over montmorillonite and synthetic montmori-

132

llonite in their Na- form conform to class 'S' and that on illite,

kaolinite and dickite, conform to class 'L' according to the cla­

ssification of Giles et al, (I96O). It suggests that the MBC

adsorption vary with the nature of clay mineraHs under study. Since

the clay minerals were all in their Na- form, hence the structural

difference among the clays play an important role in MBC adsorp­

tion. As the montmorillonite clays are swelling clays, the MBC

molecules meet strong competition with solvent water molecules for

the adsorption sites while in the case of illite, kaolinite and

dickite which have decreasing swelling properties, MBC molecules

does not meet any competition with the water molecules.

The order of MBC adsorption for various clay minerals

is as follows: montmorillonite >synthetic montmorillonite>

illite >• kaolinite •> dickite which obeys the values of their CBC

and surface area.

The adsorption data were fitted in Freundlich equation

in its linearized form (Murali and Aylmore, 1983).

Vn x/m = KC or log x/m = log K + 1/ ^ log C

where x/m is the amoimt of MBC adsorbed per 'm* mass adsorbant,

C is the equilibrium MBC concentration; K and Vn are constants.

A plot of log x/m Vs log C gave a straight line (Fig, 15).

The values of adsorption capacity (K) and intensity (1/n) were

TABLE - XXX

in

ADSORPTION OF MBC ON Na-MONTMORILLONITE

Amount of Na-montmori l loni te t aken

Concen t ra t ion of MBC s o l u t i o n added

T o t a l volume of

Volume of MBC s o l u t i o n added

(ml)

2 . 5

5.0

10.0

20 .0

30 .0

40 .0

6 0 . 0

80 .0

100.0

120.0

t h e suspension

Absorbance a t

280 nm

0.005

0.013

0.026

0.045

0.055

0.086

0.145

0.201

0.268

0.318

..

B

m

0 .5

10

g

ppm

250 ml

. Amount of MBC i n equ i l ib r ium suspension

Oug/ ml)

0.061

0.150

0.286

0.503

0.618

0.962

1.608

2.238

2.980

3.539

Amount of MBC adsorbed

(Aig/ ml)

19.50

25.00

57.00

1A8.50

291.00

319.00

396,00

481.00

510.00

630.50

m

TABLE - XXXI

ADSORPTION OF MBC ON Na-SYNTHETIC MONTMORILLONITE

Amount of Na-

Concentration

syn, montmorillonite taken =

of KBC solut ion added =»

Total volume of the suspension

Volume of MBC Absorbance solut ion added a t

(ml) 280 nm

2 .5

5.0

10.0

20.0

30.0

^ . 0

60.0

80.0

100.0

120.0

0.005

0.014

0.028

0.0A8

0.067

0.092

0.151

0.215

0.272

0.335

~

Amount of MBC i n equilibrium suspension

( ^g /ml )

0.063

0.155

0.309

0.529

0.7A0

1.020

1.678

2.390

3.020

3.720

0.5 g

10 ppm

250 ml

Amount of MBC adsorbed

(yUg/g )

18.50

22.50

45.50

135.50

230.00

290.00

361.00

405.00

490.00

540.00

133

TABLE - XXXII

ADSORPTION OF MBC ON Na- ILUTE

Amoxmt of Na- i l l i t e t aken = 0 . 5 g

Concen t ra t ion of MBC s o l u t i o n = 10 ppm added

T o t a l volume of t h e suspension = 25o ml

Volume of MBC so lu t ion added

(ml)

2.5

5.0

10.0

20.0

30.0

AO.O

60.0

80.0

100.0

120.0

Absorbance a t

280 nm

0.006

0.015

0.027

O.OAS

0.084

0.110

0,163

0.231

0.277

0.339

Amount of MBC i n equilibrium suspension

(^g / ml)

0.070

0.163

0.297

0.538

0.929

1.223

1.809

2.569

3.078

3.770

Amount of MBC adsorbed

(MS/g )

15.00

18.50

51.50

131,00

135.50

188,50

295.50

315.50

461,00

515.00

13G

TABLE - XXXIII

ADSORPTION OF MBC ON Na- KADUNITE

Amount of Na- kao l in i t e taken = 0,5 g

Concentration of MBC solut ion = 10 ppm added

Total volume of the suspension = 250 ml

Volume of iVlBC s o l u t i o n added

(ml)

2 . 5

5.0

10.0

20 .0

3 0 . 0

^ . 0

6 0 . 0

80 .0

100.0

120.0

Absorbance a t

280 nm

0.008

0.017

0.052

0.062

0.096

0.127

0.191

0.254

0.319

0.377

Amount of MBC i n equ i l ib r ium suspension

(/Ug/ml )

0.089

0.184

0.359

0.689

1.069

1.410

2.120

2.820

3.549

4.190

Amount of MBC adsorbed

( / i g /g )

5.50

8 .00

20 .50

55,50

65 .50

95 .00

140,00

190,00

225,50

305.00

137

TABLE - XXXIV

ADSORPTION OF MBC ON Na- DICKITE

Amount of Na- dickitetaken = 0.5 g

Concentration of MBC solution = 10 ppm added

Total volume of the suspension = 250 ml

Volume of MBC so lu t ion added

(ml)

2 .5

5.0

10.0

20.0

30.0

40.0

60.0

80.0

100.0

120.0

Absorbance at

280 nm

0.008

0.017

0.033

0.063

0.097

0.128

0.196

0.257

0.323

0.385

Amount of MBC i n equilibrium suspension

(Aig/ml)

0.092

0.188

0.364

0.699

1.078

1.420

2.179

2.858

3.590

4.276

Amount of MBC adsorbed

( jug /g )

4.00

6.00

18.00

50.50

61.00

90.00

110.50

171.00

205.00

261.00

138

TABLE - XXXV

FREUNDLICH CONSTANTS FOR THE ADSORPTION OF MBC ON

N a - CLAYS AT 30^C.

Type of Na- clays Freundlich constants

« Vn

Na- montmorillonite 239.25 0.931

Na- synthetic 199.35 0,932 montmorillonite

Na- illite 155.22 0.933

Na- kaolinite 63.62 1.o67

Na- dickite 53.62 1,115

13^

TABLE - XXXVI

EFFECT OF SOIL ORGANIC MATTER (SOM) ON THE ADSORPTION ON Na- MONmORILLONITE.

Amount of Na- montmor i l lon i t e taken

Concen t ra t ion of MBC s o l u t i o n added

T o t a l volume of t h e suspension

Volume of MBC s o l u t i o n added

(ml)

AO

100

40

100

40

100

40

100

40

100

40

100

Amoiont of SOM added

0 .1

0 . 2

0 . 4

0 .6

0 .8

1.0

Absorbance a t

280 nm

0.079

0.248

0.072

0.234

0,059

0.220

0.051

0.212

0.043

0.206

0.038

0.200

= 0 . 5

10

OF MBC

g

ppm

=» 250 ml

Amount of MBC i n equ i l ib r ium suspension

(Aig/ml)

0.879

2.760

0.800

2.603

0.660

2.449

0.563

2.356

0.A80

2.289

0.419

2.223

Amount of MBC adsorb ­ed

(^ig/g )

360.50

620.00

400.00

698.50

470.00

775.50

518.50

822.00

560.00

855.50

590.50

888.50

140

TABLE - XXXVII

EFFECT OF SOIL ORGANIC MATTER (SOM) ON THE ADSORPTION OF MBC ON Na- ILLLTE.

Amount of Na- i l l i t e t aken = 0 , 5 g

Concen t ra t ion of MBC s o l u t i o n = 10 ppm added

T o t a l volume of t h e suspension = 250 ml

Volume of MBC Amount of Absorbance Amount of Amount of s o l u t i o n added SOM added a t MBC i n MBC adsorb-

(ml) (%) 280 nm equ i l i b r ium ed suspension ( ^ g / g )

( ^g /ml )

AO

100

4o

100

40

100

40

100

40

100

40

100

0.1

0.2

0.4

0.6

0 .8

1.0

0.108

0.269

0.103

0.262

0.095

0.248

0.086

0.237

0.079

0.227

0.073

0.220

1.199

2.990

1.1A9

2.910

1.050

2.755

0.960

2.630

0.876

2.520

0.809

2.440

200.50

505.00

225.50

545.00

275.00

622.50

320.00

685.00

362.00

740.00

395.50

780.00

TABLE - XXXVIII

EFFECT OF SAND ON THE ADSORPTION OF MBC ON Na- MONTMORILLONITE

Amount of Na- montmorillonite taken

Concentration of MBC solution added

Total volume of the suspension

0,5 g

10 ppm

250 ml

Volume of MBC solution added

(ml)

Amount of sand added

(g/g)

Absorbance Amount of MBC Amount of at in equilibrixim MBC adsorb-

280 nm suspension ed (Aig/ml) (Aig/g)

40

100

40

100

40

100

40

100

40

100

40

100

0.01

0.02

0.04

0,06

0.08

0.10

0.088

0.272

0.090

0.275

0.092

0.281

0.095

0.287

0.097

0.292

0.099

0.297

0.980

3.025

0.995

3.060

1,024

3.123

1.055

3.184

1.080

3.241

1.103

3.295

310.00

488.50

302,50

470,00

288,00

438,50

272.50

408.00

260,00

379,50

248.50

352,50

U2

TABLE - XXXIX

EFFECT OF SAND ON THE ADSORPTION OF MBC ON Na- ILUTE.

Amount of Na- i l l i t e taken Concentration of MBC solut ion added Total volume of the suspension

0.5 g 10 ppm

250 ml

Volume of Amount of MBC solution sand added added

(ml) (g/g)

Absorbance Amount of MBC Amount of at in equilibrium MBC adsorb-280 nm suspension ed

(Mg/ml) (/ug/g )

40

100

40

100

40

100

40

100

40

100

40

100

0.01

0.02

0.04

0.06

0.08

0.10

0.112

0.286

0.115

0.292

0.119

0.500

0.121

0.507

0.124 .

0.514

0.127

0.520

1.249

5.180

1.275

5.240

1.519

5.550

1.544

5.410

1.580

5.489

1.410

5.555

175.50

410.00

162.50

580.00

140.50

555.00

128,00

295.00

110,00

255.50

95.00

222.50

H:I

TABLE - XL

EFFECT OF ADDED AI2O, AND Fe203 ON THE ADSORPTION OF MBC ON

Na- MONTMORILLONITE.

Amount of Na- montmorillonite taken • 0.5 g Concentration of MBC solution added = 10 ppm Total volume of the suspension « 250 ml

Volume of MBC Amount of Absorbance Amount of MBC Amount of solution metal oxide at in equilibrium MBC adsorb-added added 280 nm suspension ed

(ml) {%) (Mg/ml) (Aig/g )

ALUMINIUM OXIDE (Al20^)

AC

100

40

100

40

100

40

100

40

100

40

100

0.1

0.2

0.4

0.6

0.8

1.0

0.081

0.261

0.077

0,256

0.070

0.247

0.065

0.239

0.062

0.232

0.060

0.229

0.899

2.903

0.850

2,844

0.775

2.740

0.720

2.655

0.689

2.583

0.670

2.540

350.50

548.50

375.00

578,00

412.50

630.00

440.00

672.50

455.50

708.50

465.00

730.00

w

TABLE - XL (Contd.)

Volume of Amount of Absorbance Amount of MBC Amount of MBC solution metal oxide at in equilibrium MBC adsorb-added added 280 nm suspension ed

(ml) (%) (Mg/ml) (Aig/g )

IRON OXIDE

40

100

40

100

40

100

40

100

40

100

40

100

(Fe203)

0 .1

0 .2

0 . 4

0 .6

0 . 8

1.0

0.076

0.255

0.070

0 . 2 ^

0.061

0.236

0.054

0.226

0.051

0.221

0.049

0.217

0.840

2.835

0 .775

2.756

0.680

2.619

0.599

2.516

0.570

2.450

0.543

2.409

380.00

582.50

412.50

622.00

460,00

690,50

500.50

742.00

515.00

775.00

528.50

795.50

Hil

TABLE - XLI

EFFECT OF ADDED Al^O, AND Fe^O, ON THE ADSORPTION OF MBC ON

Na- ILLITE.

Amount of Na- illite taken

Concentration of MBC solution added

Total volume of the suspension

0.5 g 10 ppm

250 ml

Volume of Amount of Adsorbance MBC solution metal oxide at added added 280 nm

(ml) W

Amount of l C Amount of in equilibrium MBC adsorb-suspension ed

(Aig/ml) (Aig/g)

ALUMINIUM OXIDE (AI2O,)

40

100

40

100

40

100

40

100

40

100

40

100

0.1

0.2

0.4

0.6

0.8

1.0

0.108

0.272

0.106

0.268

0.103

0.261

0.101

0.257

0.099

0.253

0.097

0.251

1.199

3.026

1.175

2.979

1.l4o

2.900

1.119

2.850

1,104

2.809

1.080

2.789

200.50

487.00

212.50

510.50

230.00

550.00

240.50

575.00

248.00

595.50

260.00

605.50

lis

TABLE - XLI (Contd.)

Volume of Amount of Absorbance Amount of MBC Amount of MBC solution metal oxide at in equilibrium MBC adsorb-added added 280 nm suspension ed

(ml) (%) (Aig/ml) (Aig/g)

IRON OXIDE

40

100

AO

100

40

100

40

100

40

100

40

100

(Fe203)

• 0.1

0 . 2

0 . 4

0 .6

0 . 8

1.0

0 .104

0.266

0.100

0.260

0.094

0.250

0.092

0.243

0.090

0.239

0.088

0.237

1.160

2.955

1.109

2.890

1.04o

2.779

1,020

2.7O0

1.004

2.655

. 0.980

2.633

220.00

522.50

245.50

555.00

280.00

610.50

290.00

650.00

298.00

672.50

310.00

683.50

147

TABLE - XLII

EFFECT OF pH ON THE ADSORPTION OF MBC ON Na- MONTMORILLONITE

Amount of Na- montmorillonite taken » 0,5 g

Concentration of MBC solution added = 10 ppm

Total voliome of the suspension = 250 ml

Volume of MBC solution added

(ml)

pH of the suspension

Absorbance Amount of MBC Amount of at in equilibrium MBC adsorb-

280 nm suspension ed ( /ml) ipg/g)

ho

100

40

100

40

100

40

100 12

0.077

0.229

0.086

0.241

0.093

0.250

0.097

0.259

0.860

2.539

0.960

2.680

1.030

2.779

1.080

2.880

370.00

730.50

320.00

660.00

285.00

610.50

260.00

560.00

TABLE - XLIII

EFFECT OF pH ON THE ADSORPTION OF MBC ON Na «ILLITE

Amount of Na- i l l i t e taken

Concentration of MBC solut ion added

0.5 g

10 ppm

Total voliome of the suspension = 250 ml

HH

Volume of MBC solution added

(ml)

Ao

100

40

100

40

100

40

100

pH of the suspension

3

6

9

12

Absorbance a t

280 nm

0.109

0.272

0.118

0.303

0.125

0.316

0.126

0.320

Amoxmt of MBC i n equilibrium suspension (pg/ml)

1.210

3.020

1.316

3.369

1.390

3.509

1.401

3.550

Amount of MBC adsorb, ed

( ^ i g / g )

195.00

490.00

142.00

315.50

105.00

245.50

99.50

225.00

2.0 4-0 6-0 8'0 10.0 U-O

Co-ncC/^j/rwlJ-^

FIG. 13. STANDARD CURVE OF MBC

700 r

0

;Na-Montmori l loni te -•-* No-Synthetic Montmorillonite -«- iNa- IU i te -x-iNa-Kaolini'te -A-;Na-Die kite

1-0 2-0 3-0 A'O 5-0 Equil ibrium concentration (/jg/ml)

FIG-14. ADSORPTION ISOTHERMS OF MBC ON No-CLAYS AT 30°C.

3-0 r

2-5

2-0

X

^ V 5

1-0

0-5 -

0

r'lUonite etic Montmrillonite

ite A - } HQ- Dicki tc

-2 -1 log C

FIG.15 FREUNDLICH ADSORPTION ISOTHERMS OF MBC OVER Na-CLAYS AT 30°C.

900

800

700

600

500

_ ^0 0 en

^ 3 0 0

200

100 -XI

o

o o ^ 8 0 0

0 700

D GOO O

1 500

Z,00

300

200

100

r-

^

'fy' - / ' . < ^

y y

- /3 y

/

.^^ * ^X-

> •)<•

1 1

(a ) ^^^^

^^^'^

. / ' y*

^ - o ' ' ' ^

yO-

.^ ^ ^ ^¥r

^ ^ ^

1 1 1

0-2 0-4 0-6 0-8 1-0 S0M(7o) added

J>-^'

- _ . ^ . ^ o _ - - o __-o--2

t-;-^^' . _ _ - ^ — - ) ^ — • > t - - i

Curves 1 to 4 for AI2O3

Curves 5 to 8 for Fe203

J I I 1 1

0 0-2 0.4 0-6 0-8 1-0 Sesquloxide(7o) added

(b)

MBC, 800 >jg/g clay MBC,2000>jg/g clay

"»«---. - . -^ - - »

^ - - - ) f - _

0 0-02 0 0 6 010 Sand added (g/g)

(d)

^vL--^ °''---. 0 ~

"^^

- X - ^ _

0 6

PH 12

F16.1G INFLUENCE OF (o) SOIL ORGANIC MATTER (b) SAND (c) FREE A l - i Fe OXIDES AND (d) SUSPENSION pH ON THE ADSORPTION OF MBC ON {-o- ) MONTMORILLONITE AND ( - M - ) ILLITE SURFACES.

149

estimated from the intercept and slope of the curves respectively

and are given in Table- XXX V . It shows that the values of K

decrease in the same order as found in the case of adsorption iso­

therms. While the adsorption intensity of MBC over montomorillonite

and synthetic montmorillonite is about half of the intensity for

other clays. These results again confirm the earlier observation

from adsorption isotherm that there is a strong competition for

adsorption sites in montmorillonite and synthetic montmorillonite

than the other clays under study.

The effect of soil organic matter on the adsorption of MBC

is shown in Table-XXXVI and XXXVII and Fig. 16(a). It is evident

that an addition of SOM to the clay mineral increases the MBC adsorp­

tion. It may be due to the increase in adsorption sites as well as

in surface area of the clay due to SOM-clay complexation. This

also shows that the order of MBC adsorption between two clays studi­

ed remained the same as montmorillonite >• illite. While in the case

of sand addition to clay minerals, MBC adsorption reduced (Table-

XXXVIII and XXXIX Fig. I6b) due_ to the physical barrier created thereby

blocking the MBC particle toYeach adsorption sites.

Table- XL and XLI and Fig,l6c show that the addition

of Al- and Fe- oxides increased the MBC adsorption over clay mine­

rals due to increased adsorption sites(Lindsay, 1979). It may be

explained as Free oxides of Al- and Fe- added to clay suspension,

get hydrolyzed and coordinate with MBC molecules through hydrogen

150

bonding and/or Vander Waal's forces according to the suspension

pH, However, the interaction of AlpO^ or Fe^O, with clay minerals

can not be ruled out. Hence, there is a possibility of blocking

of adsorption sites of the clay particles which is evident from

the slow increase in the MBC adsorption (Fig, l6c).

Table-XLH&XLHL and Fig, 16(d) show that the effect of

suspension pH on the adsorption of MBC on to the clay surfaces. It

shows that the MBC adsorption decreases with increase in suspension

pH at both the levels of added MBC, At low pH values, the MBC gets

protonated to become a positively charged molecules and their sub­

sequent adsorption over clay surfaces may be plausible e:q)laination

for its increased adsorption in acidic pH range (Aharonson and

Kafkafi, 1975) while at high pH values, the MBC adsorption decreases

due to their hydrolysis. However, the decrease in adsorption is

slow, but even at pH 12, the adsorption was observed. This suggests

the involvement of hydrogen bonding, Vander Waal's forces and/or

coordination through cations etc, in adsorption process (Khan and

Bansal, 1980).

iSj

REFERENCES

AHARONSON, N. and KAFKAFI, U.; J. Agric. Food Chem., 23, 434 (1975).

BAUDE, F.J., PEASE, H.L., and HOLT, R.F.; J. Agric. Food Chem,, 22, 423 (1974).

CHLBA, M.j J. Agric. Food Chem,, 25(2), 368 (1977).

DESAI, M.V.M. and GANGULI, A.K,; J. Indian Chem. Soc, 56, 1167 (1979).

GILES, C.H., McEWAN, T.H., NAKHWA, S.N. and SMITH, D,; J. Chem. Soc, 3973 (1960).

HENDRICKS, S.B, and DYAL, R.S.; Trans. 4th Inter. Congr. Soil. Sci., 2, 71 (1950).

JACKSON, M.L.; 'Soil Chemical Analysis', Prentice Hall, Englewood Cliffs, NJ, p. 57 (1958).

KHAN, S. and BANSAL, V.; J. Colloid Interface Sci., 78, 554 (1980).

KHAN, S. and KHAN, N.N.; Clay Research (1986).

KHAN, S., KHAN, N.N. and KHAN, F.A.; Clay Research (1987).

LINDSAY, W.L.; 'Micronutrients in Agriculture', Soil Sci. Soc. Am. Madison (1972).

MURALI, V. and AYLMORE, L.A.G.; Soil Sci., 135, 203 (1983).

RAM, V. and VIR, D.j Pesticides, 18, 65 (1984).

SANDHJ, K.S. and GILL, S.P.S.; Pesticides, 16, 17 (1982).

152

PAPERS FUBUSHED AND CX)MMUNICATED

1. The Influsnce of organic acids and bases on the mobility

ot some heavy metals through Aligarh so i l .

Indian Soc, Soil Sc i , , 33, 779-784 (1985),

2. Pesticide mobility in soi ls as affected by the i r chemical

characterist ics and some soil properties.

Environ. Pollut. (Revised and communicated).

3 . Adsorption of Cu *, Pb * and Zn * with Ca-saturated

i l l i t e .

Clay Research (Commuxiicated).

A. Studies on the adsorption of methyl, 2-benzimidazole

carbamate (MBC) with clays as affected by various soi l

parameters.

Soil Science. (Communicated).

Influence of Organic Acids and Bases on the Mobility of Some Heavy Metals in Soil

SAMIULLAH KHAN, N . NAZAR KHAN AND NUSRAT IQBAL

Chemistry Section, Z.H. College of Engineering and Technology, Aligarh Muslim University, Aligarh, Uttar Pradesh, 202001

Abstract: The influence of organic acids and their sodium salts, amino acids and organic bases on the mobility of some heavy metals through the soil was examined by using thin layer chromatography. The organic acids, i.e., formic, acetic and oxalic ; and amino acids i.e., glycine, alanine and valine have increased the mobility of heavy metals. However, no marked influence could be observed in the case of organic bases, i.e., nicotine and pyridine. The results have been explained on the basis of reaction mechanism of complex formation, their stability, molecular size, pH and the nature of the heavy metals in soil solutions. (Key words : Heavy metals, influence, mobility in soil, organic acids and bases, thin layer chromatography)

Among various organic compounds, carboxylic acids (Schwartz et al. 1954), amino acids (Rending 1951 ; Sowden 1956) and organic bases like nicotine (Shtompel et al. 1981 ; Hanks et al. 1980) and pyridine (Vasil'chenko et al. 1975 ; Martin et al. 1977) have been found to occur or were used in soils. These organic compounds were found to interact with soil colloids (Smith 1934; Greenland et al. 1962; Brindley & Moll 1965 ; Khan & Singhal 1967 ; Theng 1974) and afifect the metal ion translocation in soil and consequently their availability to plants. However, their specific roles in the translocation of heavy metals have not yet been studied. In

another paper from this laboratory (Khan et al. 1982), it has been reported that the heavy metals translocate in soil as metal-soil organic matter (SOM) complexes. The purpose of the present study was to under­stand the role of carboxylic acids, amino acids and organic bases in the mobilization of certain heavy metals like Pb, Cd, Ni, Hg and Ag, using soil thin layer chromato­graphy.

Materials and Methods

The soil used in these investigations was an illitic fine sandy loam (depth 0-30 cm) from Aligarh district in Uttar Pradesh. Its physicochemical properties

J. Indian Soc. Soil Sci Vol. 33 : 779-84,1985

no JOtJRNAI. OF TbB INblAl) SOtlEtY OF SOlL SClEKefi (Vol. 3S

were as follows: sand 33.4% ; organic matter 0.40% ; pH 8.8 (1 : 2.5 soil: water); EC 4.8x10-4 mhos/cm; CEC 16.3 m.e./ 100 g ; exchangeable Ca 3.5, Mg 1.2, Na 1.0, K0.5m.e/100g.

The soil was dried and ground to pass through a 100 mesh sieve. It was slurried with distilled water and coated on glass plates (20x20 cm) with the help of a conventional TLC applicator to give a uniform layer of 0.5 mm thickness in each case. The plates were then air dried at room temperature (30°C). Two lines were scribed at 3 and 13 cm from the base so that a 10 cm distance could be used for development in all cases. A 0.1 M solution of metal nitrate was applied at the base line of TLC plates as a single spot (0.006 ml) with the help of a micropipette. The plates were wrapped with a wet strip of filter paper at the bottom of the plates (about 2.5 cm) to prevent disintegration of soil and then developed with distilled water or amended solutions in closed chambers. The developed plates were air-dried at room temperature (30°C) and the heavy metals, Pb, Ag and Hg were detected by spraying 0.5% (w/v) ethanolic solution of haematoxylin, which gave a violet colour­ed spot. Ni and Cd were visualised as red spots by spraying dimethylglyoxime and 1% (w/v) dithizone in CCI4 respectively. The heavy metal mobility was measured in terms of R/ values.

To study the effect of organic acids and their Na-salts, and of amino acids and organic bases, an aqueous solution of each of them with varying concentrations was taken and used as developer, the soil being the static phase.

Results and Discussion

An examinat'on of table 1 shows that the mobility of heavy metals through soil with and without organic matter (3o% H2O2 treatment) follows the order : Ni>Cd>Hg>Ag>Pb. The results are in accordance with the earlier observations of Lund et al. (1976) and Khan et al. (1982) that the heavy metals move as their soluble metal-SOM complexes in soil according to their ion size (Table 1) and compbxing nature. The decomposition of soil organic matter enhances the heavy metal mobility, thereby substantiating the clay-metal-SOM interactions (Theng 1974).

The effect of carboxylic acids on the mobility of heavy metals is given in fig. 1, which follows the order : fo rmioace t io oxalic acids; which may be attributed to the solubility of metal carboxylates (Table 1). Further the mobility increases with increase in the concentration of acids. The relative order of the mobility of metals in the acid medium was: Ni>Cd>Hg>Ag>Pb;except in the case of acetic acid, with which the order was: Hg>Cd>Ni>Ag>Pb, the order being inversely related to the instabi­lity constants of their acetate salts. Thus, the ion size, instability constants and solu­bility of metal carboxylates seem to deter­mine the extent of their mobility in soil.

The results were further verified by using the sodium carboxylate systems (Fig. 2). The translocation in presence of organic acids and their salts could be explained by considering the mobilization of heavy metals in soil as a result of for­mation of metal carboxylates. The heavy

1985] M6ilLITY OF HfeAVV METALS iJ* SOtti m

Table 1. ^ffect of organic matter on the mobility of heavy metals in soil; metal ion size*, instability constants^ and solubility' of the metal carboxylate

Heavy metals

Nickel

Cadmium

Mercury

Lead

Silver

R/ value

S.ilwitb organic maiter

0.18

0.17

0.15

0.08

0.13

Soil \vi tiout organic matter

0.32

0.29

0.25

0.15

0.21

Ion size parameter >< 10'cm

6

5

5

4

3

Instability constant of metal acetate

0.016

0.0017

3.75x10-'

0.038

0.183

Solubility in water (g/iOO g)

Mttal formate

Soluble

Very soluble

0.4

1.6

...

Metal aceta e

16.6

Very soluble

0.75

45.61

0.72

Metal oxalate

Insoluble

0 00337

Insoluble

0.00016

0.0034

o-Preiser and Fernando (1966) 6—Yetsimirsku and Vasil'ev (1959) c—Weast and Selby (1966)

Ni, »Cd, oHg, * Ag. xPb

OXALIC ACID

0 8

0.0 0 5 1.0 15 2.0 0 0 0.5 1.0 15 20 0 0 0.10 0.25

Concentration of Car boxy lie acids (mole/I it re)

Fig. I Effect of some carboxylic acids on the mobility of heavy metals in soil

0.50

7«2 JOURNAL OP THE INDIAN SOCIBTV OF SOIL SCIBNCB £Vol. 3i

N i , »Cd , o Hg, t A 5 , K P!>

' O r FORMATC

0 :

OG

0 4

0 2

I

I 0 0

. /

-o^

O X A L A T E

0 0 0 5 •>- i S 2 0 c 0 0 : 10 15 2 ' 0 0 0 01 ^1 p" r \!t^CT of Sod i jmcarbo\y l3 te5(mol»s / l i t re )

Fig 2 Effect of sodium salts of orgaoic acids on the mobility of metals in soil

0 50

metal ions combine with carboxylate ions as follows:

mM»++(n-l)X'»- :^ [M« X,,.!,]"-* ...I

mM»++n X"*- ;;i [M„ X„lf> .II

mM»+(n+1) X*"- ;;± [M„ X(„+i,]»- ...III

Increased concentration of carboxylate ions favours the formation of negatively charged metal carboxylate (III) which lowers the adsorption of these species over the negatively charged sites of soil colloids and hence increases the mobility.

In the case of salt systems, the pH increased from- 8,8 to 9.2. Most of the metal ions may be considered to remain in the form of MOH (monovalent), MOH+ and/or M(0H)2° (divalent) which can form

their respective metal carboxylates as

( / r . \R-C-O. . .H-OM/

0... /

- c \

H 1 0 1

.(IV)

.(V)

O M

and/or

R - O ,0...H- -O'

\ O . . . H - 0 - M y .,.(VI)

As the salt concentration increases, the negatively charged species (VI) may be formed thereby enhancing its mobility against the negatively charged soil colloids.

The effect of some amino acids is shown in table 2. The mobility of heavy metals generally increases with increase in the

1985] MOBILITY OF HEAVY METALS IN SOILS 783

Table 2. Effect of amino acids on mobility {Rf values) of some heavy metals in soil

Heavy metal

Nickel

Cadmium

Sil-er

Mercury

Lead

Glycine (moles/litre)

0.0

0 !8

0 17

013

0 15

0.08

0.01

0.42

0.17

0.19

0.20

0 07

0.05

0.60

0.15

0 25

0.20

0 07

0.10

0.70

0.20

0.30

0.25

0 08

Alanine (moles/litre)

00

0.!8

0.17

0.13

0.15

0 08

0.01

0.32

0.17

0.15

0.15

0 09

0 05

0.80

018

0.30

0.34

0.09

0.!0

0.89

0.21

0.35

0 35

0.09

Valine (rnoles/litre)

0.0

0.18

0.17

0.13

0.15

0.08

0.01

0.53

0.17

0.21

0.15

0.10

0.05

0.83

0.16

0.24

0.29

0.09

0.10

0.93

0 20

0.35

0.40

0.09

concentration of amino acids. The order of heavy metal mobility in soil is found to be: valine>alanine>glycine, which is in ac­cordance with their own mobilities in soil (Singbal et al. 1978), while the relative order of the mobility of heavy metals in soil was : Ni>Hg>Ag>Cd>Pb; except in the case of glycine, where the order is : Ni>Ag>Hg>Cd>Pb As the pH of the soil solution becomes alkaline (,8.3), the amino acids are expected to remain in their anionic forms (Theng 1974), because pH>pI (isoelectric point). These anionic forms of the amino acids may combine with the heavy metals as follows:

R - C H N H - C C -|-M(OH)+-^

R-CHNH—C<^

H I

o o I

O—M

...(VII)

The instability constant of these metal-amino acid complexes were reported (Yatsimirsku & Vasil'ev 1959) in the re­verse order of the mobility. The larger molecular size of amino acid restricts the

adsorption of its metal complex on the interlamellar surfaces (Talibudeen 1955) and, therefore mobilises it faster. Thus, the stability and size of heavy metal amino acid complex (VII) decide the mobility of these metals in the soil environment.

The effect of organic bases such as nicotine and pyridine on the mobility of heavy metals is shown in table 3. It is evident that nicotine and pyridine have no marked influence on the heavy metal translocation in soil. However, a slight decrease in the mobility is observed in some cases, which may be attributed to the metal-base soil complex formation. As the pH of the system upon the addition of these bases remains above 7 (8.3 in this case), the lone pair of nitrogen may attract the heavy metals through hydrogen bond­ing (Singhal &. Singh 1972) as follows :

I —N: -l-H.O . H-OH—M-Y„

-> —N...H—0-M-Y„-fH20 ...(VIII) I

where, Y=soil colloids and M is heavy metal with n+ charge.

^84 JOURNAL OF tHE INDIAN SOCIETY OF SOIL SCIENCE [Vol.33

Table 3. Effect of organic bases on the mobility (J?/ values) of heavy metals in soil

Heavy metal

Nickel

Cadmium

Silver

Mercury

Lead

Nicolir

0 00

0.18

0 17

0.13

015

0C8

le (moles/litre)

0 002

0.17

0.11

0.09

0.09

0 08

0 008

0.14

0.11

('.08

0.09

0 08

0 050

015

0.10

0.08

0.09

0 08

Pyridine

0.00

0.18

0.17

0.13

0.15

0.08

fmol.s/iitrc)

0.0C2

0,(7

0.16

0.11

0.13

0,09

0.008

0.17

0.16

0.11

0.11

O.IO

0.050

0.15

0.16

0.11

0.10

0.10

Thus, the complexation of heavy metal with bases as well as soil colloids immobilize them in soil.

Acknowledgement

The financial support from Indian Council of Agricultural Research (ICAR), New Delhi, is thankfully acknowledged.

References

Brindley, G.W. & Moll, W.F. (Jr.) (1965) Am. Miner. 50, 1355.

Preiser, H. & Fernando, Q.( 1966)/ortic Equilibria 'n Analytical Chemistry, John Wiley, New York.

Greenland, D.J., Laby, R H. & Quirk, J.P. (1982) Trans. Farad. Soc.SS,i29.

Hanks, A.R„ Schronk, L.R. & Amst, T.C. (1980) / . Liq. Chromal. 3,1087.

Khan, S., Nandan, D & Khan, N.N. (1982) Envir. Ponut.(Ser.B.),4,n9.

Khan, S. & Singhal, J P. (1967)5o/7 Sci. 104,427.

Lund, L.J., Pagi, A.L. & Nelson, CO. (1976) / . envir. Qual. 5, 330.

Mani •, F , Sa.z-Ji,iienez, C. & Can, A. (1977) Soil, Sd.Soc. Am. J. 41, l i U .

Rending, V.V. (1951) Soil Sci. 71. 253.

S.-hwartz, S.M., Warner, J.E. & Mariin, W.P. (1954) Proc. Soil Sci. Soc. Am. 18, 174.

Shtompel, Yu. A., Murzinova, l.F. & Kots>uba, M.A. (m\) Agrokhimiya, 3,99.

Singhal, J.P., Khan, S. & Bansal, V. (1978) Proc. Indian natn. Sci. Acad. 44, 267,

Singhal, J.P. & Singh, R.P. (1972) Indiun J. Chem. 10 1100.

Smith, C.R. (1934) / . Am. chem. Soc. 56,1561.

Sowden, F.J. {\956) Soil Sci. 82, 491.

Talibudeen, O. (1955) Trans. Farad. Soc. 51, 582.

Theng, B.K.G. (1974) The Chemistry of Clay Organic Reactions (1st ed.) Adam-Hilger, London.

Vasil'chenko, V.F,, Abramova, K.A., Dubrovskaja, A.A. & II'Nitskaya, L.P. (1975) Simp. Siran-chelnov. SEV 10th 2, 34.

Weast, R.C. & Selby, S.M. (1966) Handbook of Chemistry and Physics (47th ed.), Chemical Rubber Co., Ohio.

Yatsimirsku, K.B. & Vasil'ev, V.P. (1959) Instability Constants of Complex Compounds, Consultants Bureau Enterprises, Inc., New York.

{Received November 1983, A ccepted September 1985)