chapter 6shodhganga.inflibnet.ac.in/bitstream/10603/37779/12/12_chapter 6.pdfcarbamate pesticides...

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Chapter 6

Potential of Cationic Surfactant Modified Silica Gel in

Removal of Monocrotophos from Aqueous Solution

6.1 Introduction

6.1.1 Pesticides/Insecticides

Pesticides are substances meant for attracting, seducing, destroying or mitigating any pest [1]

.

They are a class of biocide. The most common use of pesticides is as plant protection

products (also known as crop protection products), which in general protect plants from

damaging influences such as weeds, diseases or insects. This use of pesticides is so common

that the term pesticide is often treated as synonymous with plant protection product, although

it is in fact a broader term, as pesticides are also used for non-agricultural purposes. The term

pesticide includes all of the following: herbicide, insecticide, insect growth regulator,

nematicide, termiticide, molluscicide, piscicide, avicide, rodenticide, predacide, bactericide,

insect repellent, animal repellent, antimicrobial, fungicide, disinfectant (antimicrobial), and

sanitizer [2]

.

In general, a pesticide is a chemical or biological agent (such as a virus, bacterium,

antimicrobial, or disinfectant) that through its effect deters, incapacitates, kills, or otherwise

discourages pests. Target pests can include insects, plant pathogens, weeds, mollusks, birds,

mammals, fish, nematodes (roundworms), and microbes that destroy property, cause

nuisance, or spread disease, or are vectors for disease. Although there are benefits to the use

of pesticides, some also have drawbacks, such as potential toxicity to humans and other

animals. According to the Stockholm Convention on Persistent Organic Pollutants, 9 of the

12 most dangerous and persistent organic chemicals are pesticides [3, 4]

.

6.1.2 Types of Pesticides/Insecticides

Pesticides are often referred as according to the type of pest they control. Pesticides can also

be considered as either biodegradable pesticides, which will be broken down by microbes and

other living beings into harmless compounds, or persistent pesticides, which may take months

or years before they are broken down: it was the persistence of DDT, for example, which led

[317]

to its accumulation in the food chain and its killing of birds of prey at the top of the food

chain. Another way to think about pesticides is to consider those that are chemical pesticides

or are derived from a common source or production method [5]

.

Some examples of chemically-related pesticides are:

Organophosphate Pesticides

Organophosphates affect the nervous system by disrupting the enzyme that regulates

acetylcholine, a neurotransmitter. Most organophosphates are insecticides. They were

developed during the early 19th century, but their effects on insects, which are similar to

their effects on humans, were discovered in 1932. Some are very poisonous (they were

used in World War II as nerve agents). However, they usually are not persistent in the

environment [6]

.

Carbamate Pesticides

Carbamate pesticides affect the nervous system by disrupting an enzyme that regulates

acetylcholine, a neurotransmitter. The enzyme effects are usually reversible [6]

.

Carbamate insecticides act by a similar mechanism to organophosphate pesticides, but

have a shorter duration of action. They are widely used, & have varying degrees of

toxicity. Like organophosphate pesticides, they interfere with the conduction of signals in

the nervous system of insects, and in cases of poisoning with high levels of exposure to

humans [7]

.

Organochlorine Insecticides

They were commonly used in the past, but many have been removed from the market due

to their health and environmental effects and their persistence (e.g., DDT and chlordane)

[6].

Pyrethroid Pesticides

They were developed as a synthetic version of the naturally occurring pesticide pyrethrin,

which is found in chrysanthemums. They have been modified to increase their stability in

the environment. Some synthetic pyrethroids are toxic to the nervous system [6]

.

Sulfonylurea Pesticides

[318]

This includes nicosulfuron, a broad-spectrum pesticide that kills plants by inhibiting the

enzyme acetolactate synthase [8]

.

Biopesticides

Biopesticides are certain types of pesticides derived from such natural materials as

animals, plants, bacteria, and certain minerals. For example, canola oil and baking soda

have pesticidal applications and are considered biopesticides. At the end of 2001, there

were approximately 195 registered biopesticide active ingredients and 780 products [6]

.

Biopesticides fall into three major classes:

Microbial pesticides consist of a microorganism (e.g., a bacterium, fungus, virus, or

protozoan) as the active ingredient. Microbial pesticides can control many different

kinds of pests, although each separate active ingredient is relatively specific for its

target pest[s]. For example, there are fungi that control certain weeds, and other fungi

that kill specific insects.

The most widely used microbial pesticides are subspecies and strains of Bacillus

thuringiensis, or Bt. Each strain of this bacterium produces a different mix of proteins,

and specifically kills one or a few related species of insect larvae. While some Bt's

control moth larvae found on plants, other Bt's are specific for larvae of flies and

mosquitoes. The target insect species are determined by whether the particular Bt

produces a protein that can bind to a larval gut receptor, thereby causing the insect

larvae to starve.

Plant-Incorporated-Protectants (PIPs) are pesticidal substances that plants produce

from genetic material that has been added to the plant. For example, scientists can take

the gene for the Bt pesticidal protein, and introduce the gene into the plant's own

genetic material. Then the plant, instead of the Bt bacterium, manufactures the

substance that destroys the pest. The protein and its genetic material, but not the plant

itself, are regulated by EPA.

Biochemical pesticides are naturally occurring substances that control pests by non-

toxic mechanisms. Conventional pesticides, by contrast, are, in general, synthetic

materials that directly kill or inactivate the pest. Biochemical pesticides include

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substances, such as insect sex pheromones (i.e. biochemicals used to disrupt the mating

behavior of insects), that interfere with mating, as well as various scented plant

extracts that attract insect pests to traps. Because it is sometimes difficult to determine

whether a substance meets the criteria for classification as a biochemical pesticide,

EPA has established a special committee to make such decisions [6]

.

The term pesticide also includes these substances:

Defoliants: Cause leaves or other foliage to drop from a plant, usually to facilitate harvest.

Desiccants: Promote drying of living tissues, such as unwanted plant tops.

Insect growth regulators: Disrupt the molting i.e. maturity from pupal stage to adult, or

other life processes of insects.

Plant growth regulators: Substances (excluding fertilizers or other plant nutrients) that alter

the expected growth, flowering, or reproduction rate of plants.

6.1.3 Organo Phosphorous Pesticides/Insecticides

In health, agriculture, and government, the word "organophosphates" refers to a group

of insecticides acting on the enzyme acetyl cholinesterase. The term is used often to describe

virtually any organic phosphorus (V)-containing compound, especially when dealing with

neurotoxic compounds. Many of the so-called organophosphates contain C-P bonds.

Organophosphate pesticides irreversibly inactivate acetylcholinesterase, which is essential to

nerve function in insects, humans, and many other animals. Organophosphate pesticides

affect this enzyme in varied ways, and thus in their potential of poisoning. For

instance, parathion, one of the first OPs commercialized, is many times more potent

than malathion, an insecticide used in combatting the Mediterranean fruit fly (Med-fly)

and West Nile Virus-transmitting mosquitoes.

Organophosphate pesticides degrade rapidly by hydrolysis on exposure to sunlight, air, and

soil, although small amounts can be detected in food and drinking water. Their ability to

degrade made them an attractive alternative to the persistent organochloride pesticides, such

as DDT, aldrin, and dieldrin. Although organophosphates degrade faster than the

organochlorides, they have greater acute toxicity, posing risks to people who may be exposed

to large amounts.

[320]

Commonly used organophosphates have included monocrtophos,

parathion, malathion, methyl

parathion, chlorpyrifos, diazinon, dichlorvos, phosmet,fenitrothion

[9], tetrachlorvinphos, azamethiphos, and azinphos methyl. They are widely used in

agriculture, residential landscaping, public recreation areas and in public health pest control

programs such as mosquito eradication [10]

.

They are of concern to both scientists and regulators because they work by irreversibly

blocking an enzyme that's critical to nerve function in both insects and humans. Even at

relatively low levels, organophosphates may be most hazardous to the brain development of

fetuses and young children. The EPA banned most residential uses of organophosphates in

2001, but they are still sprayed agriculturally on fruits and vegetables. They're also used to

control pests like mosquitos in public spaces such as parks. They can be absorbed through the

lungs or skin or by eating them on food [11]

.

6.1.4 Structural Features of Organophosphates

Effective organophosphates have the following structural features:

A terminal oxygen connected to phosphorus by a double bond, i.e. a phosphoryl group

Two lipophilic groups bonded to the phosphorus

A leaving group (i.e. a leaving group is a molecular fragment that departs with a pair

of electrons in heterolytic bond cleavage. Leaving groups can be anions or neutral molecules, but in

either case it is crucial that the leaving group be able to stabilize the additional electron density that

results from bond heterolysis. Common anionic leaving groups are halides such as Cl−, Br

−, and I

−,

and sulfonate esters. Common neutral molecule leaving groups are water and ammonia) bonded to

the phosphorus, often a halide [12]

.

[321]

6.1.5 Monocrotophos

Monocrotophos was developed by Shell Chemical Co. and Ciba Geigy Ltd in 1965. It was

first registered in Australia for control of various insect pests in cotton and pome fruit. Uses

were extended into potatoes, tomatoes, sweet corn, bananas, beans and cereals throughout the

1970s and 1980s. Some of the main insect pests are locusts, various aphids, mites and thrips,

green vegetable bug and budworms. Being also a persistent organic pollutant [11]

, it has been

banned in the U.S. and many other countries.

Monocrotophos, an organophosphorus compound, is a broad spectrum, systemic insecticide

and acaricide (i.e. a substance poisonous to ticks or mites) used to control sucking, chewing

and boring insects on horticultural and agricultural crops [13]

. Monocrotophos is registered for

agricultural use only & not for veterinary or public health uses.

Figure 6.1: (A) Chemical Structure of Monocrotophos, (B) Physical Appearance of Monocrotophos

(A)

(B)

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Table 6.1: General Information on Monocrotophos [14]

1. Chemical and Physical Properties

1.1 Identity

Colorless, hygroscopic crystals (tech: dark brown semi-solid).

Technical monocrotophos is at least 75% pure

1.2

Formula C7H14N05P

Chemical

Name

Dimethyl (E)-1-methyl-2-(methylcarbamoyl)vinyl phosphate

(IUPAC)

Chemical

Type Organophosphate

1.3 Solubility 1 kg/L (20°C, water), soluble in ethanol, acetone, and water;

practically insoluble in diesel, oils and kerosene

1.4 Melting

Point 54-55 °C

1.5 Reactivity

Decomposes above 38°C; unstable in short chain alcohols; half-life

in aqueous solutions range from 96 days (pH 5) to 17 days (pH 9);

monocrotophos is corrosive to black iron, drum steel and stainless

steel

1.6 Molar Mass 223.2 g/mol

1.7 Odor Mild, Ester Like [15]

2. Toxicity

2.1 General

2.1.1 Mode of

action

Monocrotophos affects the nervous system by inhibiting

acetylcholinesterase, an enzyme essential for normal nerve impulse

transmission.

2.1.2 Uptake

Monocrotophos can be absorbed following ingestion, inhalation and

skin contact

2.1.3 Metabolism

In mammals, the primary conversion products of monocrotophos are

dimethylphosphate, O-desmethyl monocrotophos and N-desmethyl

monocrotophos. N-desmethyl monocrotophos is more toxic than

monocrotophos.

2.2 Known Effects on Human Health

2.2.1

Acute

Toxicity

Symptoms

of

poisoning

The organophosphate insecticides are cholinesterase-inhibitors

(cholinesterase is an enzyme, especially acetylcholinesterase, which hydrolyses esters of

choline). They are highly toxic by all routes of exposure. When

[323]

inhaled, the first effects are usually respiratory and may include

bloody or runny nose, coughing, chest discomfort, difficult or short

breath and wheezing due to constriction or excess fluid in the

bronchial tubes. Skin contact with organophosphates may cause

localized sweating and involuntary muscle contractions. Eye contact

will cause pain, bleeding, tears, pupil constriction and blurred vision.

Following exposure by any route, other systemic effects may begin

within a few minutes or be delayed for up to 12 hours. These may

include pallor, nausea, vomiting, diarrhoea, abdominal cramps,

headache, dizziness, eye pain, blurred vision, constriction or dilation

of the pupils, tears, salivation, sweating and confusion. Severe

poisoning will affect the central nervous system, producing

incoordination, slurred speech, loss of reflexes (i.e. loss of automatic

response to a stimulus), weakness, fatigue, involuntary muscle

contractions, twitching, tremors of the tongue or eyelids, and

eventually paralysis of the body extremities and the respiratory

muscles. In severe cases there may also be involuntary defecation or

urination, psychosis, irregular heartbeat, unconsciousness,

convulsions and coma. Respiratory failure or cardiac arrest may

cause death.

2.2.2

Short and

long term

exposure

Repeated daily high level exposure may gradually lead to poisoning.

Several studies on occupationally exposed workers have been

conducted in countries with a hot climate where workers usually did

not wear protective clothing. In most cases plasma cholinesterase

was inhibited.

Some organophosphates may cause delayed symptoms beginning 1

to 4 weeks after an acute exposure that may or may not have

produced immediate symptoms. In such cases, numbness, tingling,

weakness and cramping may appear in the lower limbs and progress

to incoordination and paralysis. Improvement may occur over

months or years, but some residual impairment will remain.

[324]

6.1.6 Production, Regulation & Use of Monocrotophos

Production

Monocrotophos is a widely used insecticide. This chemical is produced by 15 manufactures

around the world, but the company Novartis accounts for around 40% of that which is

produced [16]

. Monocrotophos is also manufactured and exported by companies in India,

China, Brazil and Argentina. In India, for example, DowElanco makes monocrotophos in a

joint venture with the Indian company NOCIL [17]

. The total sales for monocrotophos

accounts for 3% of all insecticide-product sales worldwide.

Regulation

Monocrotophos is registered for use in 60 countries. Only 8 countries, which are responsible

for 60% of its use, require detailed data on performance, chemistry, safety and environmental

aspects while the remaining countries, accountable for 40% of use, only require "assessments,

summaries, or very limited data [16]

.

The use of monocrotophos on potatoes and tomatoes was withdrawn in the United States in

1985 and then all applications were discontinued in 1988 [18]

. Additionally, it is banned from

use in the European Union (EU).

Use

It is mainly used against cotton pests, but can also be used on citrus, olives, rice, maize,

sorghum, sugar cane, sugar beet, peanuts, potatoes, soya beans, vegetables, ornamentals,

tobacco, coffee, bananas, melons, green beans, bell peppers, and strawberries [16]

.

[325]

6.1.7 Entry of the Pesticides in to the Water Environment

There are four major routes through which pesticides reach the water: it may drift outside of

the intended area when it is sprayed, it may percolate, or leach, through the soil, it may be

carried to the water as runoff, or it may be spilled, for example accidentally or through

neglect [19]

. They may also be carried to water by eroding soil [20]

.

Figure 6.2: Entry of Pesticides in to the Water Environment

When we include urban water use in surface runoff, pesticide residues in municipal

wastewater fit the hydrologic model. When water enters an established body of water or

backs-up behind a barrier, it carries with it the dissolved materials that it picked up in the

media through which it flowed. It is difficult to determine how materials that become water

pollutants actually get into water sources. Often it is the action of water itself that causes

pollutants to enter bodies of water. The source of water that transports pollutants may be

natural, such as rainfall, or caused by humans, as in the case of irrigation or diversion of

water. Pollutants also may enter bodies of water by wind or by their own passive movement.

Movement of pollutants is a complex system and pesticides can come from either point

sources or nonpoint sources. Point sources are small, easily identified objects or areas of high

pesticide concentration such as tanks, containers, or spills. Non-point sources are broad,

undefined areas in which pesticide residues are present [21]

.

[326]

Water that flows across the surface, whether from rain, irrigation, or other water released

onto the surface, always flows downhill until it meets with a barrier, a body of water, or

begins to percolate into the soil [22]

.

(A) Entry of Pesticides into Surface Water

Pesticides enter surface waters through run-off, wastewater discharges, atmospheric

deposition and spills [23]

.

Atmospheric Deposition

Once pesticides enter the atmosphere either by above mentioned pathway, they are

subjected to transport over distances which can range to thousands of kilometers. At any

point during transport, they are also subject to the removal processes of wet and dry

deposition, both of which contaminate surface waters. In wet deposition, pesticides may be

trapped in snow and hail or dissolved in rain. In dry deposition, pesticides sorbed to

particles of wind-eroded soil [23]

.

Surface Runoff

Surface waters include streams, rivers, lakes, reservoirs and oceans. Streams and reservoirs

supply approximately 50% of the drinking water in the world. Surface waters receive a

portion of their water from snow melt or rainfall runoff. Pesticides susceptible to surface

runoff are those within the runoff-soil interaction zone or the top 0.5 to 1 cm of soil.

Several factors may affect the amount of pesticide present within this zone. These include

type of pesticide application, soil type, physiochemical properties and formulation type of

the pesticide, field half-life of the pesticide, atmospheric deposition of pesticides [23]

.

The pollution of aquatic system is depending on water solubility of pesticides. Water

solubility describes the amount of pesticide that will dissolve in a known amount of water.

It usually is measured in milligrams per liter of water or ppm and measures how easily a

pesticide may be washed off the crop, leach into the soil or move with surface runoff [23]

.

[327]

(B) Entry of Pesticides into Ground Water

Surface Runoff and Erosion

Runoff is the movement of water over a sloping surface. It can carry pesticides dissolved in

water and pesticides sorbed to eroding soil. The pesticides are either mixed in the water or

bound to eroding soil [23]

.

Runoff can also occur when water is added to a field faster than it can be absorbed into the

soil. Pesticides may move with runoff as compounds dissolved in the water or attached to

soil particles. The amount of pesticide runoff depends on slope, texture of the soil, soil

moisture content, amount and timing of a rainevent and type of pesticide used [23]

.

Soil erosion by water consists of two processes: i) the detachment of soil particles from the

soil surface, and ii) their subsequent transport downslope. Detachment is caused by raindrop

impact and also by the abrasive power of surface runoff, especially when the runoff water

flow has concentrated. Pesticides lost in runoff and erosion events leave the field either

dissolved in runoff water or adsorbed to eroded soil particles. However, for most pesticides

losses via runoff are considered far more important than losses via erosion, because the

amount of eroded soil lost from a field is usually small compared with the runoff volume [23]

.

Drain flow

The purpose of installing artificial subsurface drains is to prevent top soil saturation that

otherwise would impair crop development, soil trafficability and workability. The main

factors affecting pesticide inputs into surface waters via drainage are soil texture, site,

drainage system, compound properties, weather, application rate and season [23]

.

Leaching

Leaching is the movement of pesticides in water through the soil. Leaching occurs

downward, upward, or sideways. The factors influencing whether pesticides will be leached

into groundwater include characteristics of the soil and pesticide, and their interaction with

water from a rain or irrigation. Leaching can be increased when: (I) the pesticide is water

soluble, (II) the soil is sandy, (III) a rain-event occurs shortly after spraying, and (IV) the

pesticide is not strongly adsorbed to the soil [23]

.

[328]

Spray Drift

Spray drift is the airborne movement of spray droplets away from a treatment site during

application. Spray drift is affected by spray droplet size, wind speed and distance between

nozzle and target. It can damage nearby sensitive crops or can contaminate crops ready to

harvest and may be hazard to people, domestic animals, or pollinating insects. It can

contaminate water in ponds, streams, ditches and harm aquatic plants and animals [23]

.

Point sources

Point-source inputs of pesticides consist of runoff from hard surfaces, mostly farmyards,

storage facilities or roads. The contamination of hard surfaces arises from filling and

cleaning of sprayers, improper handling of tank mix left overs, leaking of faulty equipment,

incorrect storage of canisters. Of course accidental spills can occur due to leaking tanks on

the road to the field to be treated [23]

.

6.1.8 Pollution Caused by Pesticides & Remediation

The demand for food grains is likely to be doubled, for vegetables more than 2.5 times and

for fruits 5 times. Thus, increase in the consumption of pesticides is likely to be at least two

to three times more in years to come. The most important effects of the synthetic pesticides,

especially OP pesticides are water and soil pollutions, as well as the contamination of

vegetables, fruits, milk, food products and other living organisms. Pollution of the water in

the river and depleting its resources can put the lives of many people in danger. A wide range

of organic compounds may occur in feedstuffs, including OP pesticides. Pesticides that may

contaminate feeds originate from most of the major groups, including organo chlorine, OP

and pyrethroid compounds. OP pesticides are examples of agriculture pollutants that may

contaminate feed of livestock, particularly herbage. Cows grazing pastures that are sprayed

with OP produce milk with higher pesticide content than cows grazing in unsprayed pastures.

Moreover, it has also been reported that the ground water, surface water and drinking water

are contaminated with pesticide [24]

.

[329]

6.1.9 Effects of Monocrotophos & Other Pesticides on Health

Monocrotophos is principally used in agriculture, as a relatively cheap pesticide. However, it

is also used frequently as a tool to commit suicide [25]

.

In 2009 the World Health Organization asked India to ban monocroptophos, as a direct result

from the Bihar school meal poisoning incident. Monocroptophos was believed to be the

contaminant responsible for the death of 23 schoolchildren in a Bihar school. They ate a

state-provided school lunch in the district of Saran in India in July 2013 and it was suspected

that the food was adulterated with this pesticide [26, 27]

.

Assessment of Health Hazard

Human health effects are caused by 1) Skin contact: handling of pesticide products, 2)

Inhalation: breathing of dust or spray and 3) Ingestion: pesticides consumed as a contaminant

on/in food or in water. Farm workers have special risks associated with inhalation and skin

contact during preparation and application of pesticides to crops. However, for the majority

of the population, a principal source is through ingestion of food which is contaminated by

pesticides. Degradation of water quality by pesticide runoff has two principal human health

impacts. The first is the consumption of fish and shellfish that are contaminated by pesticides;

this can be a particular problem for subsistence fish economies that lie downstream of major

agricultural areas. The second is the direct consumption of pesticide-contaminated water [28]

has established drinking water guidelines for 33 pesticides. Many health and environmental

protection agencies have established “acceptable daily intake” (ADI) values that indicate the

maximum allowable pesticide daily ingestion over a person’s lifetime without appreciable

risk to the individual.

[330]

Table 6.1(A): WHO Guideline values for Chemicals from Agricultural Activities that are of Health

Significance in Drinking Water

[331]

The harmful effects of pesticides are 1) Death of the organism, 2) Cancers, tumours and

lesions on fish and animals, 3) Reproductive inhibition or failure, 4) Suppression of immune

system, 5) Disruption of endocrine (hormonal) system, 6) Cellular and DNA damage, 7)

Teratogenic effects (physical deformities such as hooked beaks on birds), 8) Poor fish health

marked by low red to white blood cell ratio, excessive slime on fish scales and gills, etc., 9)

Intergenerational effects (effects are not apparent until subsequent generations of the

organism) and 10) Other physiological effects such as egg shell thinning. These effects are

not necessarily caused solely by exposure to pesticides or other organic contaminants, but

may be associated with a combination of environmental stresses such as eutrophication and

pathogens [29, 30]

.

The ground-water from some US and Canadian provinces has been reported to contain the

residues of 39 pesticides and their metabolites [31]

. The calculation of level of allowable

pesticide for water is made depending on the exposure of children and adults exposure; the

children being 4 times more vulnerable to the pesticide toxicity than adults [32]

. Residues of

pesticides that are “severely restricted” be-cause of their serious effects on human health

were also found in significant quantities in the water sources. The pesticide residues exerting

serious effects on human health enter the water supply through leaching from soil into ground

water.

The health hazard assessment of monocrotophos is based mainly on toxicology reviews

issued by the FAO/WHO (Joint Meeting of the FAO Panel of Experts on Pesticides Residues

on Food and the Environment and the WHO Expert Group on Pesticides Residues - JMPR)

(FAO92, FAO94, FAO96), the Health, Safety, and Environment Division, Shell, The Hague,

The Netherlands (SIP85), and the Crop Protection Division, Ciba-Geigy Ltd, Basel,

Switzerland (Skr94). The toxicity profile in these reviews is obtained mainly from

unpublished reports of toxicology studies conducted for registration purposes by the chemical

companies manufacturing or marketing the compound.

Workers can be exposed to monocrotophos through inhalation of aerosols or by direct skin

contact with a formulation of the compound. Skin absorption has been demonstrated by

detection of large amounts of the metabolite dimethyl phosphate (DMP), excreted in the urine

of sprayers following 3-day monocrotophos application. Following absorption, the compound

is rapidly metabolized into breakdown products (e.g., DMP), which are mainly excreted in

the urine. There is no evidence of accumulation of the compound in any of the tissues.

[332]

Human case studies show a high acute toxicity of monocrotophos following accidental

exposures. Effects observed in these studies were typical cholinergic symptoms such as

reversible nerve weakness, paralysis, and respiratory difficulty [33]

.

Poisoning

One of the main agents for farmer suicides in India, where the annual average reported cases

was 17,366 in 2007, but thought to be up to 126,000 annually. Organophosphates cause

depression and this is a major risk factor for suicide. It is the most commonly consumed

insecticide in India, with a case fatality rate of 35% recorded, second only to methyl

parathion, and causing more than half of the deaths from pesticide poisoning in Andhra

Pradesh. In Sri Lanka, the ban of monocrotophos and endosulfan has reduced the number of

deaths from suicide. Also one of the most common causes of occupational poisoning in the

Indian states of Andhra Pradesh and Gujarat. Monocrotophos has been linked to significant

occupational poisoning in Indonesia, Philippines, Egypt, Brazil, and Central America [34]

.

6.1.10 Environmental and Agro-ecological Effects of Monocrotophos

Environmental Toxicity

1. Aquatic: very toxic to aquatic invertebrates; high hazard to aquatic invertebrates from

runoff and spray drift; toxic to shrimps and crabs; moderately toxic to fish. According

to FAO must be labeled as a marine pollutant.

Fish and other aquatic biota may be harmed by pesticide-contaminated water [35]

.

Pesticide surface runoff into rivers and streams can be highly lethal to aquatic life,

sometimes killing all the fish in a particular stream [36]

.

Application of herbicides to bodies of water can cause fish kills when the dead plants

rot and use up the water's oxygen, suffocating the fish [35]

. Some herbicides, such as

copper sulfite (CuSO3), that are applied to water to kill plants are toxic to fish and

other water animals at concentrations similar to those used to kill the plants [35]

.

Repeated exposure to sublethal doses of some pesticides can cause physiological and

behavioral changes in fish that reduce populations, such as abandonment of nests and

broods, decreased immunity to disease, and increased failure to avoid predators [35]

.

[333]

Application of herbicides to bodies of water can kill off plants on which fish depend

for their habitat [35]

.

Pesticides can accumulate in bodies of water to levels that kill off zooplankton, the

main source of food for young fish [37]

. Pesticides can kill off the insects on which

some fish feed, causing the fish to travel farther in search of food and exposing them

to greater risk from predators [35]

.

The faster a given pesticide breaks down in the environment, the less threat it poses to

aquatic life . Insecticides are more toxic to aquatic life than herbicides and fungicides

[35].

2. Birds: Monocrotphos is very toxic to birds; one of the most toxic insecticides for

birds [34]

.

American biologists tracked a group of migrating Swainson's hawks to their wintering

grounds in Argentina in the mid-1990s and found thousands of them dead from

monocrotophos poisoning. One single application of monocrotophos poisoning can

kill 7-25 birds per acre [38]

3. Mammals: very toxic to mammals. Poisoning incidents include mass bird kills (USA,

India, U, Australia, Argentina), and cows from eating sprayed foliage (India). Has

caused significant damage to wildlife, particularly birds and hares in Hungary [34]

.

Agroecological Disruption

1. Bees: very toxic to honey bees.

2. Terrestrial invertebrates: very toxic to beneficial insects including lacewings and

other predators; not compatible with IPM.

3. Soil organisms: moderately toxic to earthworms.

Resistance: at least 21 pests have developed resistance to monocrotophos, including

cotton bollworm, diamondback moth, whitefly, brown planthopper on rice, and house

mosquito [34]

.

[334]

6.1.11 Toxicity

Monocrotophos is highly acutely toxic by all routes of exposure and it is easily absorbed.

Acute Toxicity

Signs and symptoms of poisoning include bloody or runny nose, coughing, chest

discomfort, difficulty breathing, and wheezing; pain in the eyes, tears, constriction of

the pupils, and blurred vision; pallor, nausea, vomiting, diarrhoea, abdominal cramps,

headache, dizziness, salivation, sweating and confusion; lack of coordination, slurred

speech, loss of reflexes, weakness, fatigue, involuntary muscle contractions,

twitching, tremors of the tongue or eyelids, and eventually paralysis of the body

extremities and the respiratory muscles. Severe cases may involve involuntary

defecation or urination, psychosis, irregular heartbeat, unconsciousness, convulsion

and coma. Respiratory failure or cardiac arrest may cause death. The ingestion of only

120mg can be fatal [34]

.

Chronic Toxicity

1. Neurotoxicity: Like most organophosphates, it can cause neurobehavioural problems

and delayed neuropathy.

2. Cancer: Although not classified as a carcinogen, there is evidence it is mutagenic,

has caused DNA damage, chromosomal damage in human lymphocytes, and the growth

of human breast cancer cells. It is, therefore, potentially carcinogenic, with chronic

exposure more damaging than acute exposure.

3. Endocrine disruption: Evidence of endocrine (glands which secrete hormones directly into the

blood) disruption in mice and fish, including oestrogenicity.

4. Reproductive and developmental toxicity: Interruption in oestrous cycle, decrease

in healthy follicles and increase in atretic follicles in mice; in rats decreased fertility,

depressed lactation; some evidence of teratogenicity; evidence of disruption of

reproductive endocrine control in fish.

5. Immunotoxicity: Immunotoxic in birds and rats; also toxic to human lymphocytes.

6. Metabolic effects: Repeated exposure may induce type II diabetes.

[335]

Cardiotoxicity

In a recent study [39]

, Wistar rats were administered 1/50th of LD50 dosage of monocrotophos

(0.36 mg/kg body weight) orally via gavage (i.e. the administration of food or drugs by force, especially to an

animal, typically through a tube leading down the throat to the stomach) daily for three weeks. Monocrotophos

administered animals exhibited mild hyperglycemia and dyslipidemia in blood. Cardiac

oxidative stress was conferred by accumulation of protein carbonyls, lipid

peroxidation and glutathione production. The histopathology of the heart tissue authenticated

the monocrotophos induced tissue damage by showing signs of nonspecific inflammatory

changes and edema (edema is the condition characterized by an excess of watery fluid collecting in the cavities or

tissues of the body) between muscle fibres. Thus the findings of this preliminary study illustrate

the cardiotoxic effect of prolonged monocrotophos intake in rats and potent environmental

cardiovascular risk factor.

6.1.12 Precautions

Precautions have been suggested by Occupational Safety & Health Administration (OSHA).

They are as follow.

Avoid skin contact and air exposure to monocrotophos.

Avoid skin contact with all solvents.

Wear safety glasses at all times [16]

6.1.13 Environmental Fate and Contamination

The environmental fate (behaviour) of a pesticide is affected by the natural affinity of the

chemical for one of four environmental compartments [28]

: solid matter (mineral matter and

particulate organic carbon), liquid (solubility in surface and soil water), gaseous form

(volatilization), and biota. This behaviour is often referred to as “partitioning” and involves,

respectively, the determination of: the soil sorption coefficient; solubility; Henry’s Constant;

and the n-octanol/water partition coefficient. These parameters are well known for pesticides

and are used to predict the environmental fate of the pesticide. An additional factor can be the

presence of impurities in the pesticide formulation but that are not part of the active

ingredient. A recent example is the case of TFM (3-trifluoromethyl-4-nitrophenol), a

lampricide (a chemical which is designed to target the larvae of lampreys; a jawless fish, in river system before their

[336]

recruitment as parasitic adults) used in tributaries of the Great Lakes for many years for the control of

the sea lamprey [21]

. TFM is nontoxic to humans & other animals. Impact on other fish

species may be controlled by selective application during the larvae season for lampreys &

other management of its concentration. TFM does not accumulate, since it breaks down

within several days [40]

The contamination of water bodies with pesticides can pose a significant threat to aquatic

ecosystems and drinking water resources. Pesticides can enter water bodies via diffuse or via

point sources. Diffuse-source pesticide inputs into water bodies are the inputs resulting from

agricultural application on the field. These are tile drain outflow, baseflow seepage, surface

and subsurface runoff and soil erosion from treated fields, spray drift at application, and

deposition after volatilization. In contrast, point-source inputs derive from a localized

situation and enter a water body at a specific or restricted number of locations. These are

mainly farmyard runoff, sewage plants, sewer overflows, and accidental spills. There are also

point sources of pesticides from non-agricultural use, e.g. from application on roads, railways

or urban sealed surfaces such as parking lots.

Many factors, such as soil and pesticides properties, and crop management practices, govern

groundwater or surface water contamination by pesticides [41]

.

Soil: Breaks down rapidly and is not persistent.

Aquatic: Mobile in the soil and leaching to ground water is possible.

Bioaccumulation: Not bioaccumulative [34]

.

[337]

6.2 Materials & Methodology

6.2.1 Materials

a) Reagents:

Sodium Molybdate Solution (0.05M): Dissolve 12.5 gm Sodium Molybdate in

minimum amount of 5M H2SO4 & diluting up to 500 ml with 5M H2SO4

5M H2SO4 Solution: Molecular weight of H2SO4 is 98.08 gm/M. As H2SO4 is liquid

consider its density i.e. 1.84 gm/ml and take 266.5 ml of H2SO4 & make the final

volume 1L with distilled water

Stock Solution of Phosphorus: 50ppm stock solution of phosphorus was prepared by

dissolving 0.25gm of sodium dihydrogen phosphate in minimum amount of distilled

water. The solution was diluted up to 1L.

10% FeSO4: Dissolve 10gm of FeSO4 in 100ml distilled water. Use freshly prepared

solution.

Monocrotophos: Manufacturer Shivalik, Having 36% Purity

Dodecyl Trimethyl Ammonium Chloride

Note: All the reagents were of LR & AR grade.

b) Instruments:

Semi Micro Digital Weighing Balance ( RADWAG-LCGC Make, 308552 Model)

Visible spectrophotometer ( Systronic Make, 1854 Model)

6.2.2 Determination of Organo Phosphorous Pesticide – Monocrotophos in

Water/Wastewater

a) Method Used to Determine Monocrotophos:

Modified Molybdenum Blue Method was used to determine concentration of Monocrotophos

in the water at 825 nm.

[338]

b) Experiment to Determine Monocrotophos by Calibration Curve Method

Prepare 50 mg/L stock solution of Phosphate by weighing 0.25 gm Sodium

Dihydrogen Phosphate in minimum amount of distilled water. The solution was

diluted with distilled water up to 1 L.

Prepare 10 ml standard solutions of 0.5 mg/L, 1.0 mg/L, 1.5 mg/L & 2.0 mg/L by

taking 0.1 ml, 0.2 ml, 0.3 ml & 0.4 ml respectively from 50 mg/L stock solution.

Add 0.1 ml Conc. H2SO4 & 0.4 ml Conc. HCl.

Then add 10 ml Sodium Molybdate solution &/or directly add crystals of Sodium

Molybdate till you get stable blue color & 8 ml freshly prepared 10% FeSO4 solution.

Wait for 15 – 30 minutes.

Now take absorbance at 825 nm.

Take distilled water as a blank (it doesn’t make much difference in results if we take

reagent blank). Note down the absorbance & plot the calibration curve. [42]

Table 6.2: Experimental Results to Determine Monocrotophos by Calibration Curve

Standard Con. (mg/L) Abs

Blank 0.000

0.5 0.059

1.0 0.103

1.5 0.149

2.0 0.193

Figure 6.3: Calibration Curve for Monocrotophos Determination in Water & Wastewater

Calculation from Calibration Curve:

y = 0.098x

Where,

y = Absorbance

x = Concentration of Monocrotophos in

mg/L

[339]

6.2.3 Preparation of Cationic Surfactant Modified Silica Gel (CSMSG)

7500 mg/L cationic surfactant Dodecyl Trimethyl Ammonium Chloride (DTAC) in

500 ml standard measuring flask was prepared.

30 gm/L Silica Gel adsorbent (equilibrium adsorbent dosage, as per Chapter 5) was

added in the flask.

pH 6 was adjusted (equilibrium pH, as per Chapter 5) with 1N HCl & 1N NaOH.

Flasks were kept on magnetic stirrer for 30 minute (equilibrium contact time, as per

Chapter 5).

After completion of shaking period, contents of the flasks were filtered out through

ordinary filter paper.

Then the filtered solid material (30 gm/L Silica Gel+ DTAC), remaining on the filter

paper, was gently washed first with tap water & then with distilled water.

The washed solid material was then dried in hot air oven at 60 °C for 24 Hrs.

This oven dried solid powder is Cationic Surfactant Modified Silica Gel (CSMSG).

CSMSG powder was stored in plastic bottle for its further use in the removal of

organic pollutant like organo phosphorous pesticide Monocrotophos from waste water

by adsolubilization method.

[340]

6.2.4 Factors Affecting Removal of Monocrotophos by CSMSG from

Aqueous Solution

6.2.4 (A) Experimental Set Up to Study Effects of pH

Stock solution of 15 mg/L Monocrotophos was prepared.

50 ml quantity solution of high initial concentration i.e. 15 mg/L Monocrotophos was

taken in 100 ml beaker.

Such 5 numbers of sets were prepared.

Adsorbent i.e. CSMSG dosage was kept 8 gm/L.

pH of the 5 beakers were adjusted 2, 4, 6, 8, 10 respectively by adding the required

amount of 1N HCl and 1N NaOH.

Beakers were kept on the magnetic stirrer for 20 minute.

After completion of shaking, contents in the beakers were allowed to settle down for

few seconds.

Supernatant was filtered through ordinary filter paper & filtrate was collected to

measure the final concentration of Monocrotophos by using above mentioned

modified molybdenum blue method.

Readings were recorded & Graph was plotted to get equilibrium pH value.

Figure 6.4: Experimental Set up to Study Effects of pH on Removal of Monocrotophos by CSMSG

pH 2

15mg/L

Monocrotophos

+ 8 gm/L CSMSG

Contact Time

20 min.

pH 4

15mg/L

Monocrotophos

+ 8 gm/L CSMSG

Contact Time

20 min.

pH 6

15mg/L

Monocrotophos

+ 8 gm/L CSMSG

Contact Time

20 min.

pH 8

15mg/L

Monocrotophos

+ 8 gm/L CSMSG

Contact Time

20 min.

pH 10

15mg/L

Monocrotophos

+ 8 gm/L CSMSG

Contact Time

20 min.

[341]

6.2.4(B) Experimental Set up to Study Effects of Contact Time

50 ml Monocrotophos solution of 15 mg/L high initial concentration was taken in 100

ml beaker.


Dosage of the adsorbent was adjusted 8 gm/L.

PH 4 (i.e. equilibrium pH resulted from above experiment 6.2.4(A)) was adjusted for

all the beakers by adding the required amount of 1N HCl & 1N NaOH.

Beakers were kept on the magnetic stirrer for 5, 10, 15, 20, 30, 40 minute.

Beakers were allowed to stay for few seconds after shaking time.




Readings were recorded & Graph was plotted to get equilibrium contact time.

Figure 6.5: Experimental Set Up to Study Effects of Contact Time in Removal of Monocrotophos by

CSMSG

5 min.

15 mg/L

Monocrotophos

+ 8 gm/L CSMSG

pH 4

10 min.

15 mg/L

Monocrotophos

+ 8 gm/L CSMSG

pH 4

15 min.

15 mg/L

Monocrotophos

+ 8 gm/L CSMSG

pH 4

20 min.

15 mg/L

Monocrotophos

+ 8 gm/L CSMSG

pH 4

30 min.

15 mg/L

Monocrotophos

+ 8 gm/L CSMSG

pH 4

40 min.

15 mg/L

Monocrotophos

+ 8 gm/L CSMSG

pH 4

[342]

6.2.4(C) Experimental Set up to Study Effects of Adsorbent i.e. CSMSG Dosage


ml beaker.

Adsorbent dosage was varied in the range 4gm/L, 8gm/L, 12 gm/L, 16 gm/L & 20

gm/L.

pH 4 (i.e. equilibrium pH resulted from above experiment 6.2.4(A)) was adjusted &

kept constant for all the beakers by adding the required amount of 1N HCl & 1N

NaOH.

Beakers were kept on the magnetic stirrer for 20 minute. (i.e. equilibrium Contact

Time resulted from above experiment 6.2.4(B))





Readings were recorded & Graph was plotted.

Figure 6.6: Experimental Set Up to Study Effects of Adsorbent Dosage in Removal of Monocrotophos by

CSMSG

4 gm/L CSMSG +

15 mg/L

Monocrotophos

20mins. Contact Time

pH 4

8 gm/L CSMSG +

15 mg/L

Monocrotophos


pH 4

12 gm/L CSMSG +

15 mg/L

Monocrotophos


pH 4

16 gm/L CSMSG +

15 mg/L

Monocrotophos


pH 4

20 gm/L CSMSG +

15 mg/L

Monocrotophos


pH 4

[343]

6.2.4(D) Experimental Set up to Study Effects of Adsorbate i.e. Monocrotophos

Concentration

50 ml Monocrotophos solution of various high initial conc. Viz. 5 mg/L, 15 mg/L, 25

mg/L & 35 mg/L were taken in 4 numbers of glass beakers.

Dosage of the CSMSG adsorbent was kept 8 gm/L (i.e. equilibrium dosage resulted

from above experiment 6.2.4(C)).

PH 4 (i.e. equilibrium pH resulted from above experiment 6.2.4(A)) was kept constant

by adding the required amount of 1N HCl & 1N NaOH to all the beakers.

Beakers were kept on the magnetic stirrer for 20 minute. (i.e. equilibrium Contact

Time resulted from above experiment 6.2.4(B))





Readings were recorded & Graph was plotted.

Figure 6.7: Experimental Setup to Study Effects of Initial Adsorbate Conc. in Removal of Monocrotophos

by CSMSG

5 mg/L

Monocrotophos +

8 gm/L CSMSG

20mins Contact Time

pH 4

15 mg/L

Monocrotophos +

8 gm/L CSMSG

20mins Contact Time

pH 4

25 mg/L

Monocrotophos +

8 gm/L CSMSG

20mins Contact Time

pH 4

35 mg/L

Monocrotophos +

8 gm/L CSMSG

20mins Contact Time

pH 4

[344]

6.2.4(E) Effect of Temperature

50 ml Monocrotophos solution of 15 mg/L high initial concentration, resulted from

6.2.4(D), was taken in 100 ml beaker.

Such 3 numbers of sets were prepared to study the effect of temperature on removal

of Monocrotophos by CSMSG.

Adsorbent CSMSG dosage was kept 8 gm/L (i.e. equilibrium dosage resulted from

above experiment6.2.4(C)).

pH 4 (i.e. equilibrium pH resulted from above experiment 6.2.4(A)) kept constant by

adding the required amount of 1N HCl & 1N NaOH to all the beakers.

Beakers were kept on magnetic stirrer & various range of temperature Viz. 30°C,

40°C & 50°C was adjusted.

Beakers were kept on the magnetic stirrer for 20 mins (i.e. equilibrium Contact Time

resulted from above experiment 6.2.4(B)).





Readings were recorded & Graph was plotted to get equilibrium temperature.

Figure 6.8: Experimental Setup to Study Effects of Temperature in Removal of Monocrotophos by

CSMSG

30 ºC

15mg/L Monocrotophos

+ 8 gm/L CSMSG

20mins Contact Time

pH 4

40 ºC


+ 8 gm/L CSMSG

20mins Contact Time

pH 4

50 ºC


+ 8 gm/L CSMSG

20mins Contact Time

pH 4

[345]

6.2.5 Chemical Kinetic Study


ml beaker.


Dosage of the adsorbent was adjusted 8 gm/L.

PH 4 (i.e. equilibrium pH resulted from above experiment 6.2.4(A)) was adjusted for

all the beakers by adding the required amount of 1N HCl & 1N NaOH.

Beakers were kept on the magnetic stirrer for 5, 10, 15, 20, 30, 40 minute.





Readings were recorded & Graph was plotted to get equilibrium contact time.

Following three models were studied for chemical kinetic study

1) Pseudo First Order Model

The pseudo-first order kinetic model based on the solid adsorbent capacity for sorption

analysis is of the form:

Log (qe - qt) = log qe – (k1/2.303) t

Where,

qe (mg/gm)is the mass of Monocrotophos adsorbed at equilibrium

qt (mg/gm) the mass of Monocrotophos at any time (t) & K1 (min-1

) is the equilibrium rate

constant of pseudo-first order adsorption.

The values of k1 & qe are determined from the slope & intercept of the plot of Log (qe - qt)

versus t, respectively [43]

.

[346]

2) Pseudo Second Order Model

A pseudo-second order rate expression based on the sorption equilibrium capacity may be

represented as:

t / qt = 1/ k2qe2 + (1/ qe) t

Where,

k2 is the pseudo-second order rate constant (g mg-1

min-1

) [43]

.

The value of qe is determined from the slope of the plot of t/ qt versus t.

3) Intraparticle Diffusion

In order to understand the mechanism involved in the sorption process the kinetics

experimental results were fitted to the Weber’s intraparticle diffusion (Weber and Morris,

1963) model. It is reported that if intraparticle diffusion is involved in the process then a plot

of adsorbate uptake vs. the square root of time would result in a linear relationship and the

intraparticle diffusion would be the rate limiting step if this line passes through the origin.

Thus the kinetics results were analyzed by the Intraparticle diffusion model which is

expressed as

qt = kid t1/2

+ C

Where,

C is the intercept

Kid is the intra-particle diffusion rate constant.

The intra-particle diffusion rate constant was determined from the slope of linear gradients of

the plot qt versus t1/2 [43]

.

[347]

6.2.6 Batch Isotherm Studies

Isotherm experiments were conducted to investigate the relationship between the solid phase

concentration of an adsorbate & the solution phase concentration of the adsorbate at an

equilibrium condition. The removal percentage (R %) of Monocrotophos was calculated for

each run by following equation:

R (%) = [(Ci-Ce)/Ci]*100

Where, Ci and Ce are the initial & final concentration of Monocrotophos (mg/L) in the

solution [44]

. The adsorption capacity of the adsorbent for each concentration of

Monocrotophos at equilibrium was calculated using following equation:

qe (mg/g) = [(Ci-Ce)/M]*V

Where, Ci & Ce were the initial & final concentration of Monocrotophos (mg/L) in the test

solution respectively. V is the volume of solution (in Liter) & M is the mass of adsorbent

(gm) [44]

.

6.2.7 Adsorption Isotherm Studies

In the present study, various adsorption isotherm models have been used to study the

adsorption capacity and equilibrium coefficients for adsorption. Four commonly used

isotherms (viz. Langmuir, BET, Freundlich and Temkin isotherm) were studied.

1. The Langmuir Adsorption Isotherm

In the years 1916-1918 Langmuir developed the adsorption theory in its modern form.

Langmuir isotherm equation is derived from simple mass kinetics, assuming chemisorption.

It assumes that the uptake of adsorbate occurs on a homogenous surface by monolayer

adsorption without any interaction between adsorbed ions. The commonly expressed form is:

Ce/qe = [1/Q0b + 1/Q0 × Ce]

Where, Ce is the equilibrium concentration of adsorbate (mg/L) and qe is the amount of

adsorbate adsorbed per gram at equilibrium (mg/g), Q0 (mg/g) and b (L/mg) are Langmuir

[348]

constants related to adsorption capacity and rate adsorption, respectively. The values of Q0

and b were calculated from the slop and intercept of the Langmuir plot of Ce versus Ce/qe [45]

.

The Langmuir adsorption isotherm has the simplest form and shows reasonable agreements

with a large number of experimental isotherms. Therefore, the Langmuir adsorption model is

probably the most useful one among all isotherms describing adsorption, and often serves as

a basis for more detailed developments [46]

.

2. Freundlich Isotherm

Boedecker proposed in 1895 an empirical adsorption equation known as Freundlich isotherm,

because Freundlich assigned great importance to it and popularized its use. It is frequently

found that data on adsorption from a liquid phase are fitted better by the Freundlich isotherm

equation, provided that the adsorption sites are not identical, and the total adsorbed amount is

the same over all types of sites. The Freundlich isotherm is expressed as:

Log 10 qe = log 10(Kf) + (1/n) log10 (Ce)

Where, qe is the amount of adsorbate adsorbed at equilibrium (mg/g), and Ce is the

equilibrium concentration of adsorbate in solution (mg/L). Kf and n are the constants

incorporating all factors affecting the adsorption process [45]

.

The Freundlich equation is an empirical expression that encompasses the heterogeneity of the

surface and the exponential distribution of sites and their energies. According to Freundlich

equation, the amount adsorbed increases infinitely with increasing concentration or pressure.

This equation is, therefore, unsatisfactory for high coverage. At low concentration, this

equation does not reduce to the linear isotherm. In general, a large number of the

experimental results in the field of van der Walls adsorption can be expressed by means of

the Freundlich equation in the middle concentration range [45]

.

[349]

3. Temkin Isotherm

Temkin isotherm model is given by following equation:

X= a + b ln C

Where, C is the equilibrium concentration of solution (mg/L), X is amount of adsorbate

adsorbed per gram weight of adsorbent (mg/g), a and b are constants related to adsorption

capacity and intensity of adsorption and related to the intercept and slope of the plots of ln C

versus X [47]

.

4. BET Isotherm

BET isotherm was developed by Brunauer, Emmett and Teller as an extension of Langmuir

isotherm, which assumes that first layer of molecules adhere to the surface with energy

comparable to heat of adsorption for monolayer sorption and subsequent layers have equal

energies. Equation in its linearized form expressed as:

Cf/ (Cf-Cs) q = 1/Bqmax – (B-1/Bqmax) (Cf/Cs)

Where, Cs is the saturation concentration (mg/L) of the solute, Cf is solute equilibrium

concentration. B and qmax are two constants and can be evaluated from the slope and intercept

[48].

[350]

6.3 Results & Discussion

6.3.1(A) Effect of pH

The pH of an aqueous medium has an important role for the uptake of the adsorbate. Figure

6.9 shows the plot of Monocrotophos uptake by CSMSG at different initial pH ranges from 2

to 10. The pH of the solutions was maintained by adding dilute HCl or NaOH. In this study,

initial Monocrotophos concentration was fixed at 15 mg/L and the adsorbent dose at 8 g/L.

The temperature was 30 oC. It was found that removal of Monocrotophos increases from pH

2 to pH 4. At pH 2 it is 69.1 % whereas at pH 4 it is 72.6%. Then after from pH 6 onwards it

starts decreasing from 56.1 % (at pH 6) to 36% (at pH 10). The adsorption of anionic species

was favored at pH< pHpzc of the adsorbent. The pHpzc of CSMSG was found to be 10.2. At

low pH, the CSMSG became more positively charged and should have resulted in greater

adsorption of Monocrotphos at lower pH as obtained in several studies [49, 50, 51]

. But, in this

case, desorption of DTAC from silica surface started at lower pH. This desorption of DTAC

reduce surfactant coverage from the surface of Silica Gel and thereby, reduce the uptake

capacity at lower pH (<4) [47]

. Here in figure 6.10 it is shown that maximum 72.6% removal

of Monocrotophos was obtained and adsorption capacity qe was found 2.721 mg/gm at pH 4.

Table 6.3 & figure 6.9 present the effect of pH in removal of Monocrotophos by CSMSG

from Aqueous Solution. Result of %Removal of Monocrotophos by CSMSG at various pH is

given in table 6.4 & it is graphically presented in figure 6.10.

[351]

Table 6.3: Effect of pH on Adsorption of Monocrotophos by CSMSG from Aqueous Solution

High initial

conc. of

Monocrotphos

(mg/L)

Adsorbent

Dosage

Gm/L

Contact

Time

(Minute)

pH Range Absorbance

Final Conc. (x) of

Monocrotophos

(mg/L)

from Calibration

Curve

(y = 0.098x)

15 8 20

2 0.230 4.641

4 0.204 4.117

6 0.326 6.579

8 0.392 7.911

10 0.476 9.606

Figure 6.9: Effect of pH on Adsorption of Monocrotophos by CSMSG from Aqueous Solution

[352]

Table 6.4: % Removal of Monocrotophos & Adsorption Capacity of CSMSG at Different pH

High initial

conc. of

Monocrotophos

(mg/L)

Adsorbent

Dosage

Gm/L

Contact Time

(Min.) pH Range % Removal

Adsorption

Capacity qe

(mg/gm)

15 8 20

2 69.1 2.590

4 72.6 2.721

6 56.1 2.105

8 47.3 1.772

10 36.0 1.349

Figure 6.10: Effect of pH on % Removal of Monocrotophos by CSMSG from Aqueous Solution

[353]

6.3.1(B) Effect of Contact Time

One of the most effective factors affecting adsorption is agitation time or contact time.

Therefore in the present study for Monocrotophos uptake was conducted by taking the initial

concentration 15 mg/L with a fixed adsorbent dose of 8 gm/L and at a room temperature.

From the figure 6.11, 20 minute was found equilibrium for adsorption of Monocrotophos on

CSMSG. Almost 72.6% removal was observed at 8 gm/L CSMSG dosage & 4 pH. Thus, a

contact time of 20 min would be sufficient to attain the equilibrium for all the cases. The

equilibrium contact time, so found, indicates very quick reaction compared to other studies

like 90 min using fertilizer waste carbon [49]

, 450 min in case of date stone activated carbon

[50] and 7 days using granular activated carbon

[52].

This decrease in the adsorption rate with increase of time may be due to a distribution of

surface sites that cause decrease in adsorbent - adsorbate interaction with increasing surface

density [45]

. It may be explained by the fact that optimum adsorption occurs at a particular pH,

dose and time. Gradually adsorption process got slowed because initially a number of vacant

surface sites may be available for adsorption and after some time, the remaining vacant

surface site may be exhausted due to repulsive forces between the adsorbent and counter ion

binding at the surface of the adsorbate [54]

.

Below table 6.5 and figure 6.11 show the effect of contact time in removal of Monocrotophos

by CSMSG from Aqueous Solution. Results of % Removal of Monocrotophos by Silica Gel

at various contact time is given in table 6.6 & it is graphically presented in figure 6.12

[354]

Table 6.5: Effect of Contact Time on Adsorption of Monocrotophos by CSMSG from Aqueous Solution

High initial

conc. of

Monocrotophos

(mg/L)

Adsorbent

Dosage

Gm/L

Equilibrium

pH

Contact

Time

(Min.)

Absorbance

Final Conc. (x) of

Monocrotophos

(mg/L)

from Calibration

Curve

(y = 0.098x)

15 8 4

5 0.530 10.695

10 0.413 8.334

15 0.514 10.373

20 0.204 4.117

30 0.424 8.556

40 0.359 7.245

Figure 6.11: Effect of Contact Time on Adsorption of Monocrotophos by CSMSG from Aqueous Solution

[355]

Table 6.6: % Removal of Monocrotophos & Adsorption Capacity of CSMSG at Different Contact Time

High initial

conc. of

Monocrotophos

(mg/L)

Adsorbent

Dosage

Gm/L

Equilibrium

pH

Contact

Time

(Min.)

% Removal

Adsorption

Capacity qe

(mg/gm)

15 8 4

5 28.7 1.076

10 44.4 1.666

15 30.8 1.157

20 72.6 2.721

30 43.0 1.611

40 51.7 1.939

Figure 6.12: Effect of Contact Time on % Removal of Monocrotophos by CSMSG

[356]

6.3.1(C) Effect of Adsorbent Dosages

Since the adsorbent dose has significant effect on the removal of Monocrotophos, the effect

of this parameter was studied. To observe the effect of adsorbent dosage i.e. CSMSG dosage,

various range of the adsorbent dosage was selected which were 4 gm/L, 8gm/L, 12 gm/L, 16

gm/L & 20 gm/L. From the experiments it was observed that in the initial stage adsorption

increases with the increase of CSMSG dosage. % Removal of Monocrotophos increases from

5.7 % to 72.6 % as the CSMSG dosage increases from 4 gm/L to 8 gm/L. Maximum %

removal i.e. 72.6% was observed at 8 gm/L CSMSG dosage. pH was adjusted 4 & 20 minutes

Contact Time was given. So we can consider 8 gm/L as equilibrium dosage & can keep that

dosage in further studies. %removal increases with increase the adsorbent dosage. The

increase in the removal efficiency with the increased dose of adsorbent could be attributed to

the increased number of sites available for adsorption [54]

Table 6.7 & figure 6.13, shows the effect of adsorbent dosage on the removal of

Monocrotophos by CSMSG from the Aqueous Solution. Results of % removal of

Monocrotophos at various adsorbent dosages have been given in table 6.8 & it is graphically

presented in figure 6.14.

[357]

Table 6.7: Effect of Adsorbent Dosage on Adsorption of Monocrotophos by CSMSG from Aqueous

Solution

High initial

conc. of

Monocrotophos

(mg/L)

Equilibrium

Contact

Time (Min.)

Equilibrium

pH

Adsorbent

Dosage

Gm/L

Absorbance

Final Conc. (x) of

Monocrotophos (mg/L)

from Calibration

Curve

(y = 0.098x)

15 20 4

4 0.701 14.146

8 0.204 4.117

12 0.456 9.202

16 0.336 6.780

20 0.298 6.014

Figure 6.13: Effect of Adsorbent Dosage on Removal of Monocrotophos by CSMSG from Aqueous

Solution

[358]

Table 6.8: %Removal of Monocrotophos & Adsorption Capacity of CSMSG at Different Adsorbent

Dosage

High initial

conc. of

Monocrotophos

(mg/L)

Equilibrium

Contact Time

(Min.)

Equilibrium

pH

Adsorbent

Dosage

(Gm/L)

%

Removal

Adsorption

Capacity qe

(mg/gm)

15 20 4

4 5.7 0.213

8 72.6 2.721

12 38.7 1.449

16 54.8 2.055

20 59.9 2.247

Figure 6.14: Effect of Adsorbent Dosage on %Removal of Monocrotophos by CSMSG

[359]

6.3.1(D) Effect of Initial Adsorbate (Monocrotophos) Concentration

The effect of initial concentration of adsorbate Monocrtophos on the adsorption process was

studied. Here, adsorbent dose was kept 8 gm/L, pH 4 was adjusted and contact time was

given 20 minute. Initial concentration of Monocrotophos was adjusted 5 mg/L, 15 mg/L, 25

mg/L & 35 mg/L. Final conc. of Monocrotophos was observed 1.4 mg/L, 4.1 mg/L, 6.9 mg/L

& 9.5 mg/L respectively for 5 mg/L, 15 mg/L, 25 mg/L & 35 mg/L high initial concentration.

The % removal of Monocrotophos was observed 72.8%, 72.7%, 72.6% & 72.7% respectively

for 5 mg/L, 15 mg/L, 25 mg/L & 35 mg/L high initial concentration. Here, in the present

study % removal efficiency was almost same or near the same for all the high initial

concentration ranges. Therefore the adsolubilization technique used in present study can be

applied to the waste water or aquatic environment containing any concentration range of

organophosphorus group pesticide.

Table 6.9 & figure 6.15 show the effect of high initial concentration of adsorbate

(Monocrotophos) on the removal of Monocrotophos by CSMSG from the Aqueous Solution.

Results of % removal of Monocrotophos by CSMSG is given in table 6.10 & figure 6.16.

[360]

Table 6.9: Effect of Initial Adsorbate Concentration on Adsorption of Monocrotophos by CSMSG from

Aqueous Solution

Equilibrium

Adsorbent

Dosage

(Gm/L)

Equilibrium

Contact

Time

(Min.)

Equilibrium

pH

High initial

conc. of

Mnocrotphos

(mg/L)

Absorbance

Final Conc. (x)

of

Monocrotophos

(mg/L)

from

Calibration

Curve

(y = 0.098x)

8 20 4

5 0.067 1.4

15 0.203 4.1

25 0.340 6.9

35 0.473 9.5

Figure 6.15: Effect of Adsorbate Conc. on Adsorption of Monocrotophos by CSMSG from Aqueous

Solution

[361]

Table 6.10: %Removal of Monocrtophos & Adsorption Capacity of CSMSG at Different Initial

Adsorbate Conc.

Equilibrium

Adsorbent

Dosage

(Gm/L)

Equilibrium

Contact

Time

(Min.)

Equilibrium

pH

High initial

conc. of

Monocrotophos

(mg/L)

%

Removal

Adsorption

Capacity qe

(mg/gm)

8 20 4

5 72.8 0.910

15 72.7 2.726

25 72.6 4.535

35 72.7 6.364

Figure 6.16: Effect of Initial Adsorbate Conc. on %Removal of Monocrotophos by CSMSG

[362]

6.3.1(E) Effect of Temperature

To observe the effect of temperature on removal of Monocrotohos from Aqueous Solution

three different temperature ranges were selected viz. 30 °C, 40 °C & 50 °C. For the study

purpose, 3 sets were prepared. Temperature ranges were adjusted by the knob of magnetic

stirrer. Here adsorbent dosage was kept 8 gm/L & pH 4 was kept for all the sets. 20 minutes

contact time was provided. But no change in % removal efficiency was observed at diferent

temperature. From the study maximum 72 % removal of Monocrotophos was observed for all

the temperature range. Thus it can be concluded that temperature has no effect on the

Monocrotophos removal.

Table 6.11 & figure 6.17 how the effect of Temperature on the removal of Monocrotophos by

CSMSG from the Aqueous Solution. Results of % removal of Monocrotophos by CSMSG is

given in table 6.12 & its graphical presentation has been given in figure 6.18

Table 6.11: Effect of Temperature on Adsorption of Monocrotophos by CSMSG from Aqueous Solution

High initial

conc. of

Monocrotophos

(mg/L)

Equilibrium

Contact

Time

(min.)

Equilibrium

pH

Adsorbent

Dosage

Gm/L

Temp.

(°C) Absorbance

Final Conc. (x) of

Monocrotophos (mg/L)

from Calibration Curve

(y = 0.098x)

15 20 4 8

30 0.204 4.1

40 0.208 4.2

50 0.205 4.1

Figure 6.17: Effect of Temperature on Removal of Monocrotophos by CSMSG

[363]

Table 6.12: %Removal of Monocrotophos & Adsorption Capacity of CSMSG at Different Temperature

High initial

conc. of

Monocrotophos

(mg/L)

Equilibrium

Contact

Time

(Min.)

Equilibrium

pH

Equilibrium

Adsorbent

Dosage

(Gm/L)

Temp

(°C)

%

Removal

Adsorption

Capacity qe

(mg/gm)

15 20 4 8

30 72.6 2.721

40 72.0 2.701

50 72.4 2.716

Figure 6.18: Effect of Temperature on %Removal of Monocrotophos by CSMSG

[364]

6.3.2 Chemical Kinetic Study

Chemical kinetics is also known as reaction kinetics. It is the study of rates of chemical

processes. It includes investigations of how different experimental conditions can influence

the speed of a chemical reaction. In order to investigate the controlling mechanism of

adsorption process such as mass transfer & chemical reaction, a suitable kinetic model is

needed to analyze the data [53]

. In the present study, three kinetic models have been tested in

order to predict the adsorption data of CSMSG as a function of time using a Pseudo-First

Order, Pseudo-Second Order Kinetic Models & Intra-Particle Diffusion Model.

Table 6.13: Experimental Results of Chemical Kinetic Study for Uptake of Monocrotophos by CSMSG

High Initial

Conc. of

Monocrotophos

(mg/L)

Equilibrium

pH

Adsorbent

Dosage

(Gm/L)

Time

Interval

(min.)

Final Conc. of

Monocrotophos

(mg/L) from Graph

Adsorption

Capacity qt

(mg/gm)

15 4 8

5 10.695 1.076

10 8.334 1.666

15 10.373 1.157

20 4.117 2.721=qe

1. Pseudo-First Order Model

Log (qe - qt) = log qe – (k1/2.303) t

Where, qe (mg/gm) is the mass of Monocrotophos adsorbed at equilibrium, qt (mg/gm) the

mass of Monocrotophos at any time (t) & k1 (min-1

) is the equilibrium rate constant of

pseudo-first order adsorption. The values of k1 & qe are determined from the slope &

intercept of the plot of Log (qe - qt) versus t, respectively [45]

.

[365]

Table 6.14: Data Required for Pseudo First Order Kinetic Model

Time

Interval

(min.)

Final Conc. of

Monocrotophos

(mg/L) from Graph

Log (qe – qt) Adsorption Capacity qt

(mg/gm)

5 10.695 0.2162 1.076

10 8.334 0.0233 1.666

15 10.373 0.1942 1.157

20 4.117 -- 2.721=qe

Where, qe (mg/gm) = Mass of Monocrotophos Adsorbed, qt (mg/gm) = Mass of

Monocrotophos at particular time

qe = [(Initial Conc. of Monocrotophos – Final Conc. of Monocrotophos)/M)] * V

Where, V is the volume of solution (in Liter) & M is the mass of adsorbent (gm) [43]

.

Table 6.15: Pseudo First Order Kinetic Study

Time Interval (min.) Log (qe – qt)

5 0.2162

10 0.0233

15 0.1942

20 --

[366]

Figure 6.19: Pseudo First Order Kinetic Study for Removal of Monocrotophos by CSMSG

Calculation from Graph

K1/2.303 = Slope

Where, Slope from Graph = - 0.0096

i.e. K1 = - 0.0096 * 2.303 = 0.022

qe (calculated) = Antilog (intercept from graph) = Antilog (0.2279) = 1.6900

Table 6.16: Parameters of Pseudo First Order Kinetic

Adsorbent qe (mg/gm)

(Exp.)

qe (mg/gm)

(Cal.) K1 (min

-1) R

2

CSMSG 2.72 1.6900 0.022 0.300

[367]

From the above study it was observed that the present adsolubilization process does not

follow pseudo first order kinetic model. The experimental qe is 2.72 mg/gm & from graph

calculated qe value was obtained 3.3651 mg/gm. As per table 6.16 the experimental &

calculated values of adsorption capacity i.e. qe are not at all in good agreement. From the

figure 6.19, correlation coefficient value i.e. R2 was obtained 0.540 (which is very less)

indicates very poor adsolubilization characteristics. From all the above experimental as well

calculated data it was observed that the Monocrotophos removal by CSMSG does not follow

pseudo first order kinetic model.

2. Pseudo-Second Order Model

t / qt = 1/ k2qe2 + (1/ qe) t

Where, k2 is the pseudo-second order rate constant (g mg-1

min-1

) [45]

. The value of qe is

determined from the slope of the plot of t/ qt versus t.

Figure 6.20 shows the pseudo second order kinetic model.

Table 6.17: Pseudo Second Order Kinetic Model

Time Interval

t (min.) t/qt

5 1.8376

10 3.6751

15 5.5127

20 7.3502

[368]

Figure 6.20: Pseudo-Second Order Kinetic Study for Removal of Monocrotophos by CSMSG

Calculation from Graph

qe (Calculated) = 1/Slope from graph = 1/0.3675 = 2.7211

Intercept = 0.0 = 1/K2qe2

i.e. K2 = 1/ [0.0*(2.7211)2] = 1/0.0 = 0.0 gm/mg/minute

Table 6.18: Pseudo-Second Order Kinetic Parameters for Monocrotophos Adsorption on CSMSG

Adsorbent qe (mg/gm)

(Exp.)

qe (mg/gm)

(Cal.) K2 (g mg

-1 min

-1) R

2

CSMSG 2.72 2.7211 0.0 1.0

The calculated value of qe (2.7211 mg/gm) from the pseudo second order model is in very

good agreement with experimental qe value (2.72 mg/gm). The obtained value of R2 = 1.0

indicates very good rate of reaction. This suggests that the sorption system follows the

pseudo second order model. The value of kinetic constants and qe values of Monocrotophos

sorption onto CSMSG are given in table 6.18.

[369]

3. Intra-particle Diffusion Model

qt = kid t1/2

+ C

Where, C is the intercept & kid is the intra-particle diffusion rate constant. The intraparticle

diffusion rate constant was determined from the slope of linear gradients of the plot qt versus

t1/2 [45]

as shown in the figure 6.21. Parameters of Intra-particle Diffusion model are shown in

table 6.19. The values of rate constant of intra-particle diffusion are given in table 6.20.

Table 6.19: Parameters of Intra-particle Diffusion

Time Interval (min.) qt (mg/gm) √Time

5 1.076 2.2361

10 1.666 3.1623

15 1.157 3.8730

20 2.721 4.4721

Figure 6.21: Intra-particle Diffusion Study for Monocrotophos Removal by CSMSG

[370]

Table 6.20: Intra-Particle Diffusion Parameters from Graph

Adsorbent Kid C qe (Exp.)

(mg/gm)

R2

CSMSG 0.568 -0.296 2.72 0.52

The values of the intercept C provide information about the thickness of boundary later i.e.

larger the intercept, larger is the boundary layer effect. Here, intercept C is -0.296 &

experimental value of Adsorption Capacity (qe) is 2.72 mg/g. Both are not at all in good

agreement. Value of slope 0.568 is the Kid.

6.3.3 Adsorption Isotherm

1. Langmuir Isotherm

The experimental result of Langmuir isotherm for uptake of Monocrotophos (Ini. Conc. 15

mg/L) on CSMSG from Aqueous Solution is shown in table 6.21 & Langmuir constant

calculated from graph is shown in table 6.22. Graphical representation of the same is shown

in figure 6.22.

Table 6.21: Langmuir Isotherm Data for Uptake of Monocrotophos (Ini. Conc. 15 mg/L) on CSMSG from

Aqueous Solution.

Adsorbent

Dosage (gm)

Langmuir Isotherm

Ce

(Final Conc. of Adsorbate) (mg/L)

qe

(Adsorption Capacity)

(mg/gm)

Ce/qe

4 14.15 0.21 66.41

8 4.12 2.72 1.51

12 9.20 1.45 6.35

16 6.78 2.06 3.30

20 6.01 2.25 2.68

[371]

Figure 6.22: Langmuir Isotherm Plot for Uptake of Monocrotphos on CSMSG from Aqueous Solution

Table 6.22: Langmuir Constants for Uptake of Monocrotphos on CSMSG from Aqueous Solution

Q0 (mg/gm) b (L/mg) R2

0.1506 -5.6325 0.83

The experimental data & value of R2 i.e. 0.83 obtained for uptake of monocrotophos on

CSMSG have best fit for Langmuir isotherm. It indicates first layer of molecules adhere to

the surface with energy comparable to heat of adsorption for monolayer sorption and

subsequent layers have equal energies [55, 48]

. Here we can say that Langmuir isotherm

applies to each layer [55, 56 ]

.

Calculation from Graph:

Langmuir Equation: Ce/qe = [1/Qo b + 1 / Qo × Ce]

Q0 = 1/Slope = 1/6.64 = 0.1506 mg/gm

b = Intercept * Q0 = -37.40 * 0.1506 = - 5.6325 (L/mg)

[372]

2. Freundlich Isotherm

Results of modeling of the isotherms of Monocrotophos adsorption by CSMSG according to

Freundlich isotherm model is summarized in table 6.23. Graphical presentation of the

Freundlich isotherm is represented in figure 6.23. Table 6.24 shows the Freundlich constants

calculated from graph.

Table 6.23: Freundlich Isotherm Values for Uptake of Monocrotophos (Ini. Conc.15 mg/L) on CSMSG

from Aqueous Solution.

Adsorbent

Dosage (gm)

Freundlich Isotherm

Ce

(Final Conc. Of Adsorbate) (mg/L) Ce / qe Log Ce Log Ce / qe

4 14.15 66.41 1.1508 1.8222

8 4.12 1.51 0.6149 0.1789

12 9.20 6.35 0.9638 0.8028

16 6.78 3.30 0.8312 0.5185

20 6.01 2.68 0.7789 0.4281

Figure 6.23: Freundlich Isotherm Plot for Uptake of Monocrotophos on CSMSG from Aqueous Solution

[373]

Table 6.24: Freundlich Constants for Uptake of Monocrotphos (Ini. Conc.15 mg/L) on CSMSG from

Aqueous Solution.

Kf (mg/gm) n (L/mg) R2

0.0135 0.3311 0.90

Here the value of Kf i.e. adsorption capacity 0.0135 mg/gm & adsorption intensity n (rate of

adsorption) & i.e. 0.3311 L/mg is obtained from Freundlich isotherm. The value of n fulfills

the condition (0 < n < 1) of Freundlich isotherm [43, 45, 55]

. The value of n in the range 2-10

represent good, 1-2 moderately difficult and less than 1 poor adsorption characteristics [57].

The value of coefficient of correlation (R2) for CSMSG obtained is in good agreement. The

value of R2

is 0.90 indicates good adsorption. Thus CSMSG has best fit for Freundlich

isotherm.

It indicates that the adsorption sites are not identical; the total adsorbed amount is the same

over all types of sites. It encompasses the heterogeneity of the surface, exponential

distribution of sites and their energies. It reflects van der walls adsorption in the middle

concentration range [58]

. Thus uptake of monocrotophos on CSMSG has best fit for

Freundlich isotherm.

3. Temkin Isotherm


Temkin isotherm model is summarized in table 6.25. Graphical presentation of the Temkin

isotherm is represented in figure 6.24. Table 6.26 shows the Temkin constants calculated

from graph.


Freundlich Equation: Log10 qe = log 10(Kf) + (1/n) log10 (Ce)

n = 1/Slope = 1/3.02 = 0.3311

Kf = Antilog (Intercept) = Antilog (-1.87) = 0.0135

[374]

Table 6.25: Temkin Isotherm Values for Uptake of Monocrotophos (Ini. Conc.15 mg/L) on CSMSG from

Aqueous Solution.

Adsorbent

Dosage (gm)

Temkin Isotherm

Ce

(Final Conc. Of Adsorbate) (mg/L) ln C X (mg/gm)

4 14.15 2.6497 0.21

8 4.12 1.4159 2.72

12 9.20 2.2192 1.45

16 6.78 1.9140 2.06

20 6.01 1.7934 2.25

Figure 6.24: Temkin Isotherm Plot for Uptake of Monocrotophos on CSMSG from Aqueous Solution


Temkin Equation: X = a + b ln C

b = Slope = -2.04

a = Intercept = 5.82

[375]

Table 6.26: Temkin Constants for Uptake of Monocrotphos on CSMSG from Aqueous Solution

a (mg/gm) b (L/mg) R2

5.82 - 2.04 0.96

The value of correlation coefficient R2 is 0.96 indicates good agreement with Temkin

isotherm. The Temkin isotherm fits the present data because it takes into account for the

occupation of the more energetic adsorption sites at first. Here the value of adsorption

capacity is highest 2.72 mg/gm for 8 gm adsorbent dosage & then after it is decreasing but in

increasing order. It may be the reason for negative value of slope obtained from graph.

4. BET Isotherm


BET isotherm model is summarized in table 6.27. Graphical presentation of the BET

isotherm is represented in figure 6.25. Table 6.28 shows the BET constants calculated from

graph.

Table 6.27: BET Isotherm Values for Uptake of Monocrotophos (Ini. Conc.15 mg/L) on CSMSG from

Aqueous Solution.

Adsorbent

Dosage (gm)

BET Isotherm (Initial Conc. Was 15 mg/L)

Cf

(Final Conc. of

Adsorbate) (mg/L)

q

(mg/gm) Cf / Cs Cf/(Cs - Cf)*q

4 14.15 0.21 0.94 3.5282

8 4.12 2.72 0.27 1.0293

12 9.20 1.45 0.61 2.2997

16 6.78 2.06 0.45 1.6950

20 6.01 2.25 0.40 1.5038

[376]

Figure 6.25: BET Isotherm Plot for Uptake of Monocrotophos on CSMSG from Aqueous Solution

Table 6.28: BET Constants for Uptake of Monocrotphos on CSMSG from Aqueous Solution

qmax (mg/gm) B (L/mg) R2

0.2673 748.2 1

The experimental value & R2 = 1, obtained from graph, for uptake of monocrotophos on

CSMSG have best fit for BET isotherms of adsorption. Here we can say that BET isotherm as

an extension of the Langmuir isotherm to account for multilayer adsorption and Langmuir

isotherm applies to each layer [56]

. The much higher value of B i.e. 748.2 L/mg was obtained

for uptake of monocrotophos on CSMSG shows higher intensity / rate of adsorption in case

of BET isotherm.


BET Equation: Cf / (Cs-Cf)q = 1/Bqmax – (B – 1/ Bqmax) (Cf/Cs)

1/B*qmax = Intercept = 0.005; i.e. B*qmax = 200

i.e. qmax = 200 / 748.2 = 0.2673

((B – 1)/B*qmax) = Slope = 3.736

i.e. B – 1 = 3.736 * 200 mg/gm

i.e. B = 748.2 L/mg

[377]

6.4 Regeneration Study

After removal of Monocrotophos from Waste Water, CSMSG can be regenerated by using

mixture of Methanol & Acetone by following method.

10 gm of exhausted CSMSG (i.e. CSMSG after Monocrotophos removal) was taken

in a beaker.

25 ml of Methanol & 25 ml Acetone were added to it.

The beaker was kept on the magnetic stirrer for 1 Hr at room temperature. The

mixture was stirred well.

Distillation assembly was arranged.

Then after the mixture of Methanol + Acetone & Monocrotophos was collected in a

distillation flask.

Here, boiling points of Methanol & Acetone are around 56°C & Monocrotophos is

120°C.

Therefore, distillation process was conducted at 56°C & Methanol + Acetone was

distilled out in a collection beaker.

The distillate of Methanol + Acetone was collected.

The remaining Monocrotophos, in a distillation flask, was tested to measure the

concentration of Monocrotophos desorbed from the CSMSG & extracted in Methanol

+ Acetone.

The final concentration of Monocrtophos was measured by using above mentioned

Modified Molybdenum Blue method.

From the result we found 7.26 mg/L concentration of extracted Monocrotophos. The

initial high concentration of Monocrotophos was 15 mg/L & after adsolubilization by

8 gm/L CSMS it was 4 mg/L.

That means 11 mg/L of Monocrotophos was adsolubilized on CSMSG.

During Acetone treatment almost 7.26 mg/L of Monocrotophos desorbed from the

CSMSG & extracted in the Methanol + Acetone.

From the results shown in table 6.29 almost 66% Monocrotophos was recovered.

To get maximum recovery of Monocrotophos from exhausted CSMSG, re-extraction

was carried out with the mixture of Methanol + Acetone.

The final concentration of recovered Monocrotophos was measured 3.3 mg/L.

[378]

From the results shown in table 6.29 almost 88.2% Monocrotophos can be recovered

after re-extraction of Monocrotophos by mixture of Methanol + Acetone.

Still 0.44 mg/L Monocrotophos remains on CSMSG which is in very less quantity &

cannot be treated conventionally.

% recovery may be extended by using sophisticated instruments & more precise

experimental work.

Then both Monocrotophos as well as CSMSG can be reused for further production or

treatment respectively.

Table 6.29: Recovery of Monocrotophos

Initial Conc. of

Monocrotophos

(mg/L)

Final Conc. of

Monocrotophos

(mg/L)

Quantity

of

Exhausted

CSMSG

(gm)

Quantity of

Methanol +

Acetone

(ml)

Contact

Time for

Recovery

(Hr.)

Temp.

(°C)

Conc. of

Monocrotophos

Adsolubilized on

CSMSG (mg/L)

Conc. of

Monocrotophos

Extracted by

Methanol +

Acetone (mg/L)

%

Recovery of

Monocrotop

hos

1st Extraction

15 4 10 25+25 1 25

=Ini.

Conc. –

Final

Conc.

i.e.

15 – 4 =

11

7.26 66

2nd

Extraction (The residues remain after 1st extraction was retreated)

-- -- 10 25+25 1 25 11 – 7.26

= 3.74 3.3 88.2

[379]

6.5 Removal of Organophosphate Pesticide from the Wastewater Sample of

Pesticide Manufacturing Industry

To check the effectiveness of the treatment given to the synthetic sample (as described

earlier) the experiment was again performed on actual sample of Pesticide / Insecticide

Manufacturing Industry. pH, contact time & adsorbent dosage were adjusted 4, 20 minutes &

8 gm/L respectively (equilibrium from experiments 6.3.1(A), 6.3.1(B), 6.3.1(C) respectively).

Maximum 68.4% removal of Phenol from actual industrial sample by CSMSG was observed

where as it was 72.6% for synthetic sample. The results of % removal have been mentioned

in Table 6.30. From the results it was observed that the CSMSG is an effective adsorbent to

remove organic pollutant like organophosphate pesticide / insecticide from industrial

wastewater.

Table 6.30: %Removal of Organophosphate Pesticide / Insecticide from Actual Sample

Equilibrium

Adsorbent

Dosage

(Gm/L)

Equilibrium

Contact

Time

(Min)

Equilibrium

pH

High Initial

conc. of

Pesticide

(mg/L)

Absorbance

Final Conc. of

Pesticide

(mg/L)

(0.098x)

% Removal

8 20 4 6.8 0.213 2.1 68.4

6.6 Conclusion

In the present study batch experiments were carried out to observe their effect on

Monocrotophos removal by CSMSG. It was observed that the Cationic Surfactant Modified

Silica Gel can be used as an effective adsorbent in the waste water treatment for the removal

of insecticide Monocrotophos of organophosphate group. Various factors affecting

Monocrotophos removal were also studied. The variables for pH were decided 2, 4, 6, 8 & 10

to find out optimum pH for further treatment. While studying pH variables; other parameters

such as high initial concentration of Monocrotophos (15 ppm), Contact Time (20 minutes) &

Adsorbent CSMSG Dosage (8 gm/L) were kept constant. The variables for contact time were

decided as 5 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes & 40 minutes to find

out optimum contact time for further treatment. While studying Contact Time variables; other

parameters such as high initial concentration of Monocrotophos (15 ppm), pH (4 – optimum

pH obtained from previous study) & Adsorbent CSMSG Dosage (8 gm/L) were kept

constant. The variables for Adsorbent CSMSG Dosage were decided as 4 gm/L, 8 gm/L, 12

[380]

gm/L, 16 gm/L & 20 gm/L to find out optimum adsorbent dosage for further study. While

studying Adsorbent CSMSG Dosage variables; other parameters such as high initial

concentration of Monocrotophos (15 ppm), pH (4 – optimum pH obtained from previous

study) & Contact Time (20 minutes – optimum contact time obtained from Previous study)

were kept constant. The variables for adsorbate concentration were decided as 5 ppm, 15

ppm, 25 ppm & 35 ppm to find out optimum adsorbate concentration. While studying high

initial Adsorbate Concentration variables; other parameters such as pH (4 – optimum pH

obtained from previous study) & Contact Time (20 minutes – optimum contact time obtained

from Previous study) & Adsorbent CSMSG Dosage (8 gm/L) from previous study) were kept

constant. From the batch study; pH 4, contact time is 20 minutes & CSMSG - adsorbent

dosage is 8 gm/L were found optimum experimental conditions to get maximum 72.6%

removal of Monocrotophos from aqueous solution. Adsorption capacity was found 2.72

mg/gm. From the adsorbate variable study it was observed that different adsorbate

concentration did not affect Monocrotophos removal by CSMSG from aqueous solution. It

shows that the CSMSG can be used to remove Monocrotophos of any high range.

Temperature effect and chemical kinetic studies were carried out to. The variables for

temperature were decided as 30 ˚C, 40 ˚C & 50 ˚C to find out optimum temperature range. It

was observed that temperature had no effect on % removal of CSMSG & almost same %

removal efficiency was observed at all the temperature ranges. From chemical kinetic studies

it was observed that the rate of reaction of the removal followed Pseudo Second Order

Kinetic Model. The calculated value of qe (2.7211 mg/gm) from the Pseudo Second Order

Kinetic Model is in very good agreement with experimental qe value (2.72 mg/gm). The

obtained value of R2 = 1.0 indicates very good rate of reaction. From the adsorption isotherm

study the values of coefficient of correlation (R2) for uptake of Monocrotophos on adsorbent

CSMSG obtained were in good agreement with Langmuir (R2 = 0.83), Freundlich (R

2 =

0.90), Temkin (R2 = 0.96) & BET isotherms (R

2 = 1).

From the batch study; pH 4 (72.6% removal of Monocrotophos), contact time 20 min

(72.6 % removal of Monocrotophos) & adsorbent dosage 8 gm/L (72.6% removal of

Monocrotophos) were found optimum experimental conditions for maximum removal

of Monocrotophos by CSMSG from aqueous solution. From the adsorbate variable study it

was observed that different adsorbate concentration did not affect Monocrotophos removal by

CSMSG from aqueous solution. It shows that the CSMSG can be used to remove

Monocrotophos of any high range. Temperature effect and chemical kinetic studies were

[381]

carried out to. The variables for temperature were decided as 30 ˚C, 40 ˚C & 50 ˚C to find out

optimum temperature range. It was observed that temperature had no effect on % removal of

CSMSG & almost same 72% removal efficiency was observed at all the temperature ranges.

For the regeneration of CSMSG, Methanol + Acetone mixture was used. In this study it was

found that only Monocrotophos was desorbed from the CSMSG & not surfactant. Almost

88.2% recovery of Monocrotophos was observed. During recovery 10 gm of exhausted

CSMSG was treated with 50 ml of Metahnol + Acetone for 1 Hr. at 25 °C.

Temperature effect and Chemical Kinetics studies were carried out to interpret the

adsolubilization pattern. It was observed that temperature does not affect the % removal

efficiency of CSMSG & almost same % removal efficiency was observed at all the

temperature ranges. From three different chemical kinetic studies it was observed that the

adsolubilisation process follows Pseudo Second Order kinetic model. The values of

coefficient of correlation (R2) for uptake of Monocrotophos on adsorbent CSMSG obtained

are in good agreement with Langmuir, Freundlich, Temkin & BET isotherms. Values of

coefficient of correlation (R2) are nearer to 1.0. Therefore it is confirmed that the adsorption

process occurred over here follows Langmuir, Freundlich, Temkin & BET.

The removal efficiency was also checked on actual sample of pesticide industry & maximum

68.4% removal was obtained by adjusting the equilibrium values of pH, contact time &

adsorbent dosage. From the study it is confirmed that CSMSG is very good adsorbent & it

can be efficiently used in industries to remove organophosphorus pesticides from the effluent.

6.7 Recommendation

The present study suggested that CSMSG can be effectively useful in the effluent treatment

plant of pesticide or insecticide manufacturing industries for removal of Organo

Phosphosphate group pesticide/insecticide. These data can be used in designing and

fabrication of an economic treatment plant for the removal of organophosphate from pesticide

industries & any water i.e. surface run off from agriculture farm yard, surface water, ground

water containing organophosphate pesticide. By implementing this technology we can

prevent the introduction of insecticide/pesticide into adjacent water resources. These

insecticides/pesticides are extremely toxic. It is thus very important to find ways for the

[382]

removal of pesticides/insecticides from the water environment when present at high

concentration.

Pesticides/insecticides are very dangerous constituents of waste water of many industries. As

they are easily soluble in water, they can damage public health by running to the drinking

water discharge point. Cationic surfactant modified Silica Gel can adsolubilize organo

phosphorous group pesticide/insecticide efficiently from aqueous media without consuming

much energy. Again the pesticide/insecticide can be regenerated by using Methanol +

Acetone – an organic solvent & both can be separated by distillation. Thus separated

Methanol + Acetone & Monocrtophos can be re-used as extracting solvents & raw material in

the industries.

Here in the figure 6.26 probable plant lay out for the treatment of industrial effluent by

CSMSG has been given.

Figure 6.26: Treatment Layout for the Industrial Effluent by using Cationic Surfactant Modified Silica

Gel.

Waste Water

Containing

Monocrotophos

Equalization

Tank

Agitation Tank,

Where CSMSG

Dosage of 8 gm/L

can be given

pH 4 shall be

Maintained by

Adding 1N HCl or

1N NaOH

20 min. Retention

Time is provided for

the Reaction

Recycle & Reuse Treated

Water (supernatant) &

Regenerate exhausted CSMSG

(sludge) by Acetone to Recycle

& Reuse

Regeneration of exhausted

CSMSG (sludge) & Recovery of

Monocrotophos by Methanol +

Acetone to recycle & Reuse

[383]

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