agrichemical industries

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Agrichemical

Industries

PESTICIDES:

Insecticides, Fungicides and Herbicides

Agrochemical (or agrichemical), a contraction of agricultural chemical , is a generic term for

the various chemical products used in agriculture. In most cases, agrichemical refers to the broad

range of pesticides, including insecticides, herbicides, and fungicides. It may also include

synthetic fertilizers, hormones and other chemical growth agents, and concentrated stores of

raw animal manure.

Many agrichemicals are toxic, and agrichemicals in bulk storage may pose

significant environmental and/or health risks, particularly in the event of accidental spills. In

many countries, use of agrichemicals is highly regulated. Government-issued permits for purchase

and use of approved agrichemicals may be required. Significant penalties can result from misuse,

including improper storage resulting in spillage. On farms, proper storage facilities and labeling,

emergency clean-up equipment and procedures, and safety equipment and procedures for handling,

application and disposal are often subject to mandatory standards and regulations. Usually, the

regulations are carried out through the registration process.



Agrichemical Industries

2 C hemical Process Industries

Table of Contents

I. Pesticide

i. Insecticide

a. History

b. Classification

c. Manufacturing of DDT

1. R aw Materials

2. Equipment

3. Unit Operations

4. Process Flow Chart

ii. Attractants and R epellents

iii. Fumigants

a. Manufacturing of Hydrocyanic Acid

1. R aw Materials

2. Equipment

3. Unit Operations


iv. Nematacides

v. Acaricides

vi. R odenticides

vii. Fungicides

a. History

b. Classification

c. Manufacturing of Dithiocarbamate

1. R aw Materials

2. Equipment

3. Unit Operations4. Process Flow Chart

viii. Herbicides

a. History

b. Classification

c. Manufacturing of Treflan

1. R aw Materials

2. Equipment

3. Unit Operations


II. Waste Treatment





OBJECTIVES:

1. To be familiar with the agrichemical industries particularly the pesticides.

2. To know the different types of pesticide, its manufacturing process and equipment used.

3. To know the waste treatment used by plant producing pesticides.





PESTICIDES

Pesticides are substances or mixture of substances intended for preventing, destroying,

repelling or mitigating any pest.[1] A pesticide may be a chemical substance, biological agent (such

as a virus or bacterium), antimicrobial, disinfectant or device used against any pest. Pests

include insects, plant pathogens, weeds, molluscs, birds, mammals, fish, nematodes (roundworms),

and microbes that destroy property, spread disease or are a vector for disease or cause a nuisance.

Although there are benefits to the use of pesticides, there are also 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 pesticide.

Subclasses of pesticides include: herbicides, insecticides, fungicides, rodenticides, pediculicides,

and biocides.

Pesticides can be classified by target organism, chemical structure, and physical state.

Pesticides can also be classed as inorganic, synthetic, or biologicals (biopesticides), although the

distinction can sometimes blur. Biopesticides include microbial pesticides and biochemical

pesticides.[7] Plant-derived pesticides, or "botanicals", have been developing quickly. These include

thepyrethroids, rotenoids, nicotinoids, and a fourth group that includes strychnine and scilliroside.

Many pesticides can be grouped into chemical families. Prominent insecticide families

include organochlorines, organophosphates, and carbamates. Organochlorine hydrocarbons

(e.g. DDT) could be separated into dichlorodiphenylethanes, cyclodiene compounds, and other

related compounds. They operate by disrupting the sodium/potassium balance of the nerve fiber,

forcing the nerve to transmit continuously. Their toxicities vary greatly, but they have been phased

out because of their persistence and potential to bioaccumulate.

Organophosphate and carbamates largely replaced organochlorines. Both operate through inhibiting

the enzyme acetylcholinesterase, allowing acetylcholine to transfer nerve impulses indefinitely and

causing a variety of symptoms such as weakness or paralysis.

Organophosphates are quite toxic to vertebrates, and have in some cases been replaced by

less toxic carbamates. Thiocarbamate and dithiocarbamates are subclasses of carbamates. Prominent

families of herbicides include pheoxy and benzoic acid herbicides (e.g. 2,4-D), triazines

(e.g. atrazine), ureas (e.g. diuron), and Chloroacetanilides (e.g. alachlor). Phenoxy compounds tend

to selectively kill broadleaved weeds rather than grasses. The phenoxy and benzoic acid herbicides

function similar to plant growth hormones, and grow cells without normal cell division, crushing the





plants nutrient transport system. Triazines interfere with photsynthesis. Many commonly used

pesticides are not included in these families, including glyphosate.

Pesticides can be classified based upon their biological mechanism function or application

method. Most pesticides work by poisoning pests. A systemic pesticide moves inside a plant

following absorption by the plant. With insecticides and most fungicides, this movement is usually

upward (through the xylem) and outward. Increased efficiency may be a result. Systemic

insecticides, which poison pollen and nectar in the flowers, may kill bees and other

needed pollinators.

Insecticides

An insecticide is a pesticide used against insects in all developmental forms. They include

ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used

in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of

the major factors behind the increase in agricultural productivity in the 20th century. Nearly all

insecticides have the potential to significantly alter ecosystems; many are toxic to humans; and

others are concentrated in the food chain. It is necessary to balance agricultural needs with

environmental and health issues when using insecticides

HISTORY OF INSECTICIDES

The term insecticide is often times confused with the term pesticide. The main difference is

the the insecticide simply refers to just insects, whereas pesticide refers to any sort of pest which can

cause harm. Today we have many associations with the term ³insecticide.´ Some are negative

because the term conjures images of Silent Spring and others are positive because it can be used to

prevent massive crop blights, therefore preventing starvation.

Insecticides used prior to the 1940s were mostly inorganic compounds such as arsenicals.

After World War II, DDT and other chlorinated pesticides came on the market. There is no question

about the spectacular insect-controlling effects achieved on many crops, and populations of some

pests that affect both public and veterinary health were greatly diminished. The shortcomings of

these compounds, particularly their lack of selectivity and harmful environmental effects, were

eventually realized, however, leading to the termination of their use by the late 1970s. Meanwhile,

organophos-phorus and carbamate insecticides gained in popularity and have established themselves





as two of the major classes of insecticides. In more recent years, functional synthetic analogues of

naturally occurring toxic chemicals were developed. Pyrethroids, for example, are essentially

synthetic mimics of naturally occurring pyrethrins found in the flowers of species of

chrysanthemum. The synthetic neonicotinoids mimic naturally occurring nicotine from tobacco

plants. Useful microbial products were also developed in the 1980s and 1990s; examples are Bacillus

thuringiensis (Bt) toxins, avermectins, and spinosyns. Modern insecticides used today are generally

very selective, mostly affecting only the targeted pest insect. They are potent, requiring only small

quantities to achieve their effects, and they are much less persistent in the environment.

Older Insecticides

The first synthetic organochlorine insecticide, DDT (dichlorodiphenyl-trichloroethane),

discovered in Switzerland in 1939, was very effective and used extensively to control head and body

lice, human disease vectors and agricultural pests, in the decades leading up to the 1970s. Benzene

hexachloride (BHC) and chlordane were discovered during World War II and toxaphene (and

heptachlor) slightly later. Shortly thereafter, two cyclodiene organochlorines, aldrin and dieldrin,

were introduced, followed by endrin, endosulfan, and isobenzan. All these insecticides acted by

blocking an insect's nervous system, causing malfunction, tremors, and death. All organochlorines

are relatively insoluble, persist in soils and aquatic sediments, can bioconcentrate in the tissues of

invertebrates and vertebrates from their food, move up trophic chains, and affect top predators.

Organophosphate insecticides originated from compounds developed as nerve gases by

Germany during World War II. Thus, those developed as insecticides, such as tetraethyl

pyrophosphate (TEPP) and parathion, had high mammalian toxicities. In insects, as in mammals,

they act by inhibiting the enzyme cholinesterase (ChE) that breaks down the neurotransmitter

acetylcholine (ACh) at the nerve synapse, blocking impulses and causing hyperactivity and tetanic

paralysis of the insect, then death. Some are systemic in plants and animals, but most are not

persistent and do not bioaccumulate in animals or have significant environmental impacts.

Carbaryl, the first carbamate insecticide, acts on nervous transmissions in insects alsothrough effects on cholinesterase by blocking acetylcholine receptors.

Botanical insecticides include nicotine from tobacco, pyrethrum from chrysanthemums,

derris from cabbage, rotenone from beans, sabadilla from lilies, ryania from the ryania shrub,

limonene from citrus peel, and neem from the tropical neem tree.





N ewer Insecticides

Synthetic pyrethroid insecticides, with structures based on the natural compound pyrethrum, were

introduced in the 1960s and include tetramethrin, resmethrin, fenvalerate, permethrin, lambda-

cyalothrin, and deltamethrin, all used extensively in agriculture. They have very low mammaliantoxicities and potent insecticidal action, are photostable with low volatilities and persistence. They

are broad-spectrum insecticides and may kill some natural enemies of pests. They do not

bioaccumulate and have few effects on mammals, but are very toxic to aquatic invertebrates and fish.

C lasses of Agricultural Insecticides

CLASS CHARACTERISTICS

Systemic insecticides

These are incorporated by treated plants. Insects ingest the insecticide

while feeding on the plants.

Contact insecticides

These are toxic to insects brought into direct contact. Efficacy is often

related to the quality of pesticide application, with small droplets (such as

aerosols) often improving performance.

Natural insecticides Such as nicotine and pyrethrum, are made by plants as defences against

insects. Nicotine based insecticides have been barred in the U.S. since

2001 to prevent residues from contaminating foods.

Inorganic insecticides These are manufactured with metals and include arsenates copper- and

fluorine compounds, which are now seldom used, and sulfur, which is

commonly used.

Organic insecticides These are synthetic chemicals which comprise the largest numbers of

pesticides available for use today.

Mode of action Or how the pesticide kills or inactivates a pest, is another way of

classifying insecticides. Mode of action is important in predicting whether an insecticide will be toxic to unrelated species such as fish, birds and

mammals.





Heavy metals, e.g. lead, mercury, arsenic, as well as plant toxins such as nicotine have been

used for many years. Various plants have been used as folk insecticides for centuries, including

tobacco and pyrethrum. Some farmers are reporting successfully using spray of crudely fermented

alcohol as an effective insecticide.

SULFUR AND SULFUR COMPOUNDS

Dusting sulfur, elemental sulfur in powdered form, is a common fungicide for grapes,

strawberry, many vegetables and several other crops. It has a good efficacy against a wide range of

powdery mildew diseases as well as black spot. In organic production, sulfur is the most important

fungicide. It is the only fungicide used in organically farmed apple production against the main

disease apple scab under colder conditions. Biosulfur (biologically produced elemental sulfur with

hydrophilic characteristics) can be used well for these applications.

Sulfur and sulfur compounds enjoy a limited use against mice, spiders, and similar insects,

but their chief use is as fungicides. The lime sulfurs are widely applied for the control of scale

insects. Sulfur dioxide is the oldest known fumigant.

PLANT DERIVATIVES

Many of the plant derivatives used as insecticides depend for toxicity upon the alkaloids that

they contain. Some of these have been known for a long time.

Pyrethrins

There are toxic, non nitrogeneous organic

esters of chrysanthemic acid in the flowers of the

pyrethrum plant, a type of chrysanthemum. The

plant is cultivated commercially in Kenya, Japan,

the Congo, and Brazil. It is one of the oldest and

safest insecticides available. The ground, dried

flowers were used in the early 19th century as the

original louse powder to control body lice in the

Napoleonic Wars. Pyrethrum acts on insects with





phenomenal speed causing immediate paralysis, thus its popularity in fast knockdown household

aerosols. However, unless it is formulated with one of the synergists, most of the paralyzed insects

recover to once again become pests. The insecticidal action of the pyrethrins is characterized by a

rapid knockdown effect, particularly in flying insects, and hyperactivity and convulsions in most

insects. These symptoms are a result of the neurotoxic action of the pyrethrins, which block voltage-

gated sodium channels in nerve axons. As such, the mechanism of action of pyrethrins is

qualitatively similar to that of DDT and many synthetic organochlorine insecticides. In purity,

pyrethrins are moderately toxic to mammals, but technical grade pyrethrum is considerably less

toxic. Pyrethrins are especially labile in the presence of the UV component of sunlight, a fact that has

greatly limited their use outdoors.

N icotine

Tobacco plant compounds are more commonly used insecticide, fungicide, and contain a

variety of alkaloids, mainly composed of nicotine, it is actually tobacco nicotine poisoning. Nicotine

is a colorless oily liquid, slight odor, was strongly alkaline, volatile, soluble in many organic

solvents. It is extracted by several methods from tobacco, and is effective against most all types of

insect pests, but is used particularly for aphids and caterpillars--soft bodied insects. Nicotine is an

alkaloid, a chemical class of heterocyclic compounds containing nitrogen and having prominent

physiological properties. Other well-known alkaloids that are not insecticides are caffeine (coffee,

tea), quinine (cinchona bark), morphine (opium poppy), cocaine (coca leaves), ricinine (a poison in

castor oil beans), strychnine (Strychnos nux vomica), coniine (spotted hemlock, the poison used by

Socrates), and, finally LSD (a hallucinogen from the ergot fungus attacking grain). . Nicotine is a

colorless oily liquid, slight odor, was strongly alkaline, volatile, soluble in many organic solvents.

Rotenone

It is the toxic principle of several tropical plants, the chief of which is derris. While rotenone

exhibits moderate to low toxicity as a garden insecticide it is highly toxic to fish and invertebrates

and, in fact, was originally used by indigenous people to help capture fish. Rotenone is a

mitochondrial poison, which blocks the electron transport chain and prevents energy production (41).

As an insecticide it is considered a stomach poison because it must be ingested to be effective. Pure

rotenone is comparable to DDT and other synthetic insecticides in terms of its acute toxicity to

mammals, although it is much less toxic at the levels seen in formulated products. Safety of rotenone

has recently been called into question because of (a) controversial reports that acute exposure in rats

produces brain lesions consistent with those observed in humans and animals with Parkinson¶s





disease , and (b) the persistence of rotenone on food crops after treatment. Astudy of rotenone

residues on olives conducted in Italy determined that the halflife of rotenone is 4 days, and at harvest

residue levels were above the tolerance limit.

SYNTHETIC ORGANICS

The phenomenal increase in synthetic organic compounds used for insecticides since World

War II has revolutionized this country. In 1940, the combined output of synthetic organic

insecticides was but a few million pounds per year, yet in 1972, the annual production of pesticides

was more than 1150 million pounds.

Dichlorodiphen yltrichloroethane ( DDT)

Dichlorodiphenyltrichloroethane (DDT) is an insecticide used in agriculture. This compound

was first made by Zeidler in Germany in 1874, but its insecticidal properties were not discovered

until 1937. It was extensively used during World War II to control body lice and as mosquito

larvicide. It was the first chemical to have great enough residual contact action to be useful; an insect

can be killed by simply walking over dried, sprayed surface. DDT has shortcomings, which naturally

accelerated the development of other insecticides and led to the government ban on its use in the

United States in the early 1970s.

The near-worldwide ban on agricultural use of DDT and related chemicals has allowed some

of these birds--such as the peregrine falcon--to recover in recent years. A number of the

organochlorine pesticides have been banned from most uses worldwide and globally they are

controlled via the Stockholm Convention on persistent organic pollutants. These include: aldrin,

chlordane, DDT, dieldrin, endrin, heptachlor, mirex and toxaphene.





Manufacturing Process of DDT

There are several methods of DDT manufacture. The usual method is the exothermic

condensation of chloral and chlorobenzene in the presence of oleum.

It is manufacture as follows:

Alcohol is chlorinated to chloral-alcoholate in a 750-gal glass-lined chlorinator, first at

below 30ºC, but eventually up to 75 and 90 ºC (Ch). This takes place over the course of 60 to 70 h,

the temperature being controlled through water in either coils or jackets. (Op)

The overhead is conducted to a partial condenser which liquefies the alcohol from the HCl

that is absorbed later and the small amount of ethyl chloride that is vented (Ch).

The chloral-alcoholate is decomposed by H2SO

4into chloral and alcohol and purified by

distillation (Op).

The chloral and chlorobenzene are condensed, using strong H2SO4 or oleum in a glass-lined

1,000 gal reactor (Ch).

The reaction takes 5 to 6h and is controlled at 15 to 30 ºC by the brine or steam coils. The

spent acid is withdrawn (Op), and the DDT is water-washed several times (Op) and neutralized with

soda ash (Ch).

The DDT and chlorobenzene mixture is dropped to a 500-gal dryer, where steam melts the

DDT and distills any unreacted chlorobenzene overhead (Op).

The molten DDT is run to casting pans to solidify and to be ground (Op).





Equipment

1. Column 2. Chlorinator

3. Dryer 4. Condenser





C arbophos

Carbophos, the generic name applied to Malathion is a pesticide that is widely used in

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

programs such as mosquito eradication. Malathion is a pesticide that is used to kill insects on

agricultural crops, on stored products, on golf courses, in home gardens, and in outdoor sites where

trees and shrubs are grown at home; it is also used to kill mosquitoes and Mediterranean fruit flies

(medflies) in large outdoor areas. Additionally, malathion is used to kill fleas on pets and to treat

head lice on humans. It is usually sprayed on crops or sprayed from an airplane over wide land areas,

especially in the states of California and Florida. Malathion comes in two forms: a pure form of a

colorless liquid and a technical-grade solution (brownish-yellow liquid), which contains malathion

(greater than 90%) and impurities in a solvent. The technical-grade malathion smells like garlic.

Malathion is a manufactured chemical, so it is only found in the environment as a result of its

manufacture or use. Malathion has been manufactured in the United States since 1950 and has been

used to kill insects on many types of crops since this time. The Food and Drug Administration

(FDA) and the EPA allow a maximum amount of 8 parts per million (ppm) of malathion to be

present as a residue on specific crops used as foods. Because malathion can be dangerous to humans,

the EPA requires that a certain amount of time must pass between the time of application of the

insecticide and entry by a worker into a field where the chemical has been applied. Usually, at least

12 hours must pass between application and entry, but in some cases, such as when workers are

entering a field to hand harvest or hand prune the crops, time periods as long as 6 days must pass

between application and entry into the field. In this way, exposure to malathion can be controlled and

accidental exposures can be prevented.

C arbar yl

Carbaryl, also known as Sevin (1-naphthyl methyl

carbamate) is a wide-spectrum carbamate insecticide which

controls over 100 species of insects on citrus, fruit, cotton,

forests, lawns, nuts, ornamentals, shade trees, and other

crops, as well as on poultry, livestock and pets. It is also

used as a molluscicide and an acaricide. Carbaryl works

whether it is ingested into the stomach of the pest or

absorbed through direct contact. The chemical name for

carbaryl is 1- naphthol N-methylcarbamate. Carbaryl is

formulated as a solid which varies from colorless to white to gray, depending on the purity of the





compound. The crystals are odorless. This chemical is stable to heat, light and acids under storage

conditions. It is non-corrosive to metals, packaging materials, or application equipment. It is found in

all types of formulations including baits, dusts, wettable powder, granules, oil, molassas, aqueous

dispersions and suspensions. Sevin is the trade name for a widely used synthetic insecticide

containing the active ingredient carbaryl. Carbaryl belongs to the chemical class called carbamates.

As insecticides go Sevin is only moderately toxic to mammals and is still widely used in gardens and

landscapes. It is, however, highly toxic to honey bees and many other beneficial insects and mites.

P aradichlorobenzene

Paradichlorobenzene is used as a fumigant insecticide to control clothes moths. It is also

found in deodorant blocks made for trash cans and toilets. Paradichlorobenzene was first registered

for use in the United States in 1942, and it is sometimes called 1, 4-dichlorobenzene.Mothballs

containing paradichlorobenzene are solids that turn into toxic gas that kills moths. The vapor of

paradichlorobenzene is toxic to insects. In humans and other animals, paradichlorobenzene is broken

down in the body to form other compounds that may be harmful to cells or organs such as the liver.

In humans, paradichlorobenzene is distributed in the blood, fat, and breast milk. It is broken down

into several other chemicals by the body and excreted in urine. Human volunteers who inhaled

paradichlorobenzene exhaled half the dose. The amount of paradichlorobenzene in their blood

dropped by more than 50% one hour after the exposure stopped. In animals, paradichlorobenzene is

rapidly absorbed through the lungs or gut, but more slowly through the skin. Paradichlorobenzene

was found in the fat, liver, and kidneys. Smaller amounts were found in the blood plasma, lungs, and

muscle. Paradichlorobenzene was eliminated from the body soon after the exposure stopped. When

animals were exposed for long periods of time, their bodies began to break down the

paradichlorobenzene faster, and tissue levels declined. Most of the paradichlorobenzene that gets

into the environment will turn into vapor. It can also be broken down by bacteria or become

attached to sediments in water. Paradichlorobenzene that binds to soil may be taken up by plants,

and plant leaves may absorb paradichlorobenzene from the air. Paradichlorobenzene in air is broken

down slowly by other chemicals. It has been found in rainwater and snow. Paradichlorobenzene has

been found in groundwater close to a source of contamination. In air, its half-life is about 31 days.

Dimethoate

Dimethoate is an insecticide used to kill mites and insects systemically and on contact. It is

used against a wide range of insects, including aphids, thrips, planthoppers and whiteflies on

ornamental plants, alfalfa, apples, corn, cotton, grapefruit, grapes, lemons, melons, oranges, pears,





pecans, safflower, sorghum, soybeans, tangerines, tobacco, tomatoes, watermelons, wheat and other

vegetables. It is also used as a residual wall spray in farm buildings for house flies. Dimethoate has

been administered to livestock for control of botflies. Dimethoate is available in aerosol spray, dust,

emulsifiable concentrate, and ULV concentrate formulations. Dimethoate is one of a class of

insecticides referred to as organophosphates. These chemicals act by interfering with the activities of

cholinesterase, an enzyme that is essential for the proper working of the nervous systems of both

humans and insects.

M ethiocarb

Methiocarb is a chemical mainly used as a bird repellent, as an insecticide and

as molluscicide. It is toxic to humans, not listed as a carcinogen, is toxic to reproductive organs, and

a potent neurotoxin. Methiocarb can also cause acute toxicity in humans if anyone is exposed to it

for long periods of time. Methiocarb is also a known poison to water organisms.

Dichlorvos

Dichlorvos or 2,2-dichlorovinyl dimethyl phosphate (DDVP) is a highly volatile

organophosphate, widely used as a insecticide to control household pests, in public health, and

protecting stored product from insects. It is effective against mushroom flies, aphids, spider mites,

caterpillars, thrips, and whiteflies in greenhouse, outdoor fruit, and vegetable crops. It is also used in

the milling and grain handling industries and to treat a variety of parasitic worm infections in dogs,

livestock, and humans. It is fed to livestock to control bot fly larvae in the manure. It acts against

insects as both a contact and a stomach poison. It is available as an aerosol and soluble concentrate.

It is also used in pet collars and "no-pest strips" as pesticide-impregnated plastic. In this form it has

recently been labeled for use against bed bugs.

Attractants and repellents

Attractants and repellents are compounds that stimulate the directed movement

of microorganisms, in particular bacteria, towards or away from the compound. The directed

movement in response to the presence of the attractant or repellent compound is a feature of a

bacterial behavior known as chemotaxis. Various compounds can act as attractants.

Overwhelmingly, these are nutrients for the bacterium. Attractant compounds include sugars, such as

maltose, ribose, galactose, and amino acids such as L-aspartate and L-serine.





Similarly, various compounds will cause a bacterium to move away. Examples of repellents

include metals that are damaging or lethal to a bacterium (e.g., cobalt, nickel), membrane-disruptive

compounds such as indole, and weak acids, which can damage the integrity of the cell wall.

The presence and influence of attractants and repellents on the movement of bacteria has been

known for over a century. In the 1880s experiments demonstrated that bacteria would move into

capillary tubes filled with meat extract and away from capillaries filled with acids.

Now, the molecular underpinning for this behavior is better understood. The chemotaxis

process has been particularly well-studied in the related Gram-negative bacteria Escherichia

coli and Salmonellatyphimurium .

These bacteria are capable of self-propelled movement, by virtue of whip-like structures

called flagella. Movement consists typically of a random tumbling interspersed with a brief spurt of

directed movement. During the latter the bacterium senses the environment for the presence of

attractants or repellents. If an attractant is sensed, the bacterium will respond by exhibiting more of

the directed movement, and the movement will over time be in the direction of the attractant. If the

bacterium senses a repellent, then the periods of directed movement will move the bacterium away

from the compound. Both of these phenomena require mechanisms in the bacterium that can sense

the presence of the compounds and can compare the concentrations of the compounds over time.

The detection of attractants and repellents is accomplished by proteins that are part of the

cytoplasmic, or inner, membrane of bacteria such as Escherichia coli and Salmonella typhymurium.

For example, there are four proteins that span the inner membrane, from the side that contacts

the cytoplasm to the side that contacts the periplasmic space. These proteins are collectively called

the methyl-accepting chemotaxis proteins (MCPs). The MCPs can bind different attractant and

repellent compounds to different regions on their surface. For example, on of the MCPs can bind the

attractants aspartate and maltose and the repellents cobalt and nickel.

The binding of an incoming attractant or repellent molecule to a MCP causes the addition or

removal of a phosphate group to another molecule that is linked to the MCP on the cytoplasm side.

Both events generate a signal that is transmitted to other bacterial mechanisms by what is known as a

cascade. One of the results of the cascade is the control of the rotation of the flagella, so as to propel

the bacterium forward or to generate the random tumbling motion.





The cascade process is exceedingly complex, with at least 50 proteins known to be involved.

The proteins are also involved in other sensory events, such as to pH, temperature, and other

environmental stresses.

The memory of a bacterium for the presence of an attractant or repellent is governed by the

reversible nature of the binding of the compounds to the bacterial sensor proteins. The binding of an

attractant or a repellent is only for a short time. If the particular compound is abundant in the

environment, another molecule of the attractant or repellent will bind very soon after the detachment

of the first attractant or repellent from the sensor. However, if the concentration of the attractant or

repellent is decreasing, then the period between when the sensor-binding site becomes unoccupied

until the binding of the next molecule will increase. Thus, the bacterium will have a gauge as to

whether its movement is carrying the cell towards or away from the detected compound. Then,

depending on whether the compound is desirable or not, corrections in the movement of the

bacterium can be made.

Fumigants

Fumigation is a method of pest control that completely fills an area with

gaseous pesticides²or fumigants²to suffocate or poison the pests within. It is utilized for control of

pests in buildings (structural fumigation), soil, grain, and produce, and is also used during processing

of goods to be imported or exported to prevent transfer of exotic organisms. This method also affects

the structure itself, affecting pests that inhabit the physical structure, such as woodborers and dry

wood termites. Carbon tetrachloride and Hydrocyanic acid are useful fumigants.

C arbon tetrachloride

Carbon tetrachloride, also known by many other names (notably, carbon tet in the cleaning

industry, and as a Halon or Freon in HVAC, see Table for others) is the organic compound with

the formula CCl4. It was formerly widely used in fire extinguishers, as a precursor torefrigerants, and

as a cleaning agent. It is a colourless liquid with a "sweet" smell that can be detected at low levels.

Carbon tetrachloride persisted as a pesticide to kill insects in stored grain, but in 1970, it was

banned in consumer products in the United States. Prior to the Montreal Protocol, large quantities of

carbon tetrachloride were used to produce the freon refrigerants R-11 (trichlorofluoromethane) and

R-12 (dichlorodifluoromethane). However, these refrigerants are now believed to play a role





in ozone depletionand have been phased out. Carbon tetrachloride is still used to manufacture less

destructive refrigerants. Carbon tetrachloride has also been used in the detection of neutrinos.

Carbon tetrachloride is one of the most potent hepatotoxins (toxic to the liver), and is widely

used in scientific research to evaluate hepatoprotective agents

H ydroc yanic acid

It is the most widely used fumigant. It is used inside plastic tents for treating citrus trees, and

it is highly effective in the gl ass house. Large quantities are used in the citrus fruit industry and

smaller amounts for greenhouse and household fumigation. This material is very toxic to animals.

Manufacturing Process of HydrocyanicAcid

The steps in the manufacture of hydrocyanic acid are as follows:

An aqueous solution of sodium cyanide is mixed with concentrated sulfuric acid and allowed

to react. Most of the hydrocyanic acid is expelled by the heat of reaction. The remainder is removed

by heating the residual solution of sodium sulfate with live steam to 103 to 104ÛC. The mixture of

hydrocyanic acid and steam is passed through a cooler where some of the steam condenses and the

vapors are sent to a still. Water, almost free of hydrocyanic acid, is collected at the bottom of the still

and the vapor is fairly pure hydrocyanic acid. The vapors are conducted through two condensers. The

first is cooled with water and about 30 percent of the acid is liquefied. The second condenser is

cooled with brine to liquefy the remainder of the acid. The liquid hydrocyanic acid is degassed to

remove carbon dioxide impurity and is adjusted to standard concentration, stabilized with 0.005

percent by weight of sulfuric acid and packed into tinned steel drums.





Equipment

1. Cooling coil 2. Degasser

3. Tanks 4. Still





Nematicides

A nematicide is a type of chemical pesticide used to kill parasitic nematodes. One common

nematicide is obtained from neem cake, the residue obtained after cold-pressing the fruit and kernels

of the neem tree. Known by several names in the world, the tree was first cultivated in India inancient times and is now widely distributed throughout the world. The root exudate of marigold

(T agete s) is also found to have nematicidal action. Nematophagous fungi, a type of carnivorous

fungi, can be useful in controlling nematodes, P aecilomyce s being one example.

Prior to 1985, the persistent halocarbon DBCP was a widely used nematicide and

soil fumigant. However, it was banned from use after being linked to sterility among male workers;

the Dow Chemical company was subsequently found liable for more than $600 million in damages.

Besides chemicals, soil steaming can be used in order to kill nematodes. Superheated steam is

induced into the soil which causes almost all organic material to deteriorate.

Acaricides

Acaricides are pesticides that kill members of the Acari group, which

includes ticks and mites. Acaricides are used both in medicine and agriculture, although the desired

selective toxicity differs between the two fields. There are more specific words sometimes used

depending upon the targeted group. Ixodicides are substances that kill ticks and Miticides are

substances that kill mites.

R odenticides

Rodenticides are a category of pest control chemicals intended to kill rodents. Single feed

baits are chemicals sufficiently dangerous that the first dose is sufficient to kill. Rodents are difficult

to kill with poisons because their feeding habits reflect their place as scavengers. They will eat a

small bit of something and wait, and if they don't get sick, they continue. An effective rodenticide

must be tasteless and odorless in lethal concentrations, and have a delayed effect





Fungicides

Fungi are organisms which include yeasts, molds, mildews, rusts, root and stem rots, smuts,

and mushrooms. These are organisms that have no ability to synthesize their own food because they

lack true roots and chlorophyll and depend on dead plants and animals for their source of food. They

also become parasitic to living things (plants and animals) for food source, protection and as a means

of their reproductive cycle. Parasitic fungi can cause great damage to crops which would tend to

affect the economy, food supply, and even health of the people. Thus these fungi needs to be kept on

check or must be extinguished before they could do harm to people.

Fungicides are extensively used in industry, agriculture, homes and gardens for a number of

purposes, including: protection of seed grain during storage, shipment, and germination; protection

of mature crops, berries, seedlings, flowers, and grasses in the field, in storage, and during shipment;

suppression of mildews that attack painted surfaces; control of slime in paper pulps; and protection

of fabrics and carpets in homes.

History of fungicides

The first attempt to counter the fungal pests on seeds and crops has been the use of salt

solution to wash seeds. This was suggested by the clean crop salvaged from a shipwreck. When

potato blight hit Ireland on 1842, studies showed that parasitic fungus could be responsible. It took

another ten years for this idea to be accepted. Sulfur dust have been successfully used against the

powdery mildew of vines, and then copper sulphate dried off with lime had been found to give a

cleaner crop of wheat after application to the seed. Today, there are many developments with regards

to the use of fungicides in agriculture. Researches and studies are conducted to enhance the

efficiency, lessen the adverse affect on humans, animals, and the environment, and to minimize the

cost of production of fungicides.

INORGANIC FUNGICIDES

These are composed of elemental sulphur and heavy metal compounds such as copper and

mercury. However, because of environmental considerations, mercury containing fungicides have

been banned by the Environmental Protection Agency (EPA) of the United States.

E lemental Sulfur





Elemental sulfur occurs widely and abundantly in nature, both in the free state and in

combination. Deep in the earth it is found in the elemental state as sulfides and sulfates. As far as its

fungicidal value is concerned, the elemental sulfur is the most important of all these natural sources.

It occurs in many area, often as chemically pure crystals but more often mixed with gypsum and

limestone. Elemental sulfur is imported to a large extent in India every year for the formulation of

fungicides.

Sulfur alone and in combination as lime-sulfur was one of the most important fungicides. In

the 1800s and early 1900s, sulfur dust and spray were used against mildew on fruit trees. In 1958, the

weight of sulfur used against fungi was four times that of all other fungicides. However, the recent

development of

W ettable sulfur

Organic fungicides have reduced the use of sulfur along with other inorganic chemicals. It

controls fungal diseases, mites, and chiggers on lawns and plants. Also lowers the pH level and

acidifies the soil. Wettable sulfur is prepared by adding wetting and dispersing agents to finely

ground sulfur, since sulfur by itself cannot be suspended in water. They look like dusts, but they are

made to mix with water. When mixing a WP, first mix the measured quantity with a small amount of

water, forming a slurry, (a paper cup with a popsicle

stick makes a good disposable mixing container) then

add it and the additional water to the spray tank. The

spray tank must be frequently shaken to maintain the

suspension. Wettable sulphur is compatible with

nicotine sulphate and the two can be successfully used

as a dual purpose spray.

M icronized wettable sulfur

This is made by a special manufacturing process to

ensure an extremely fine particle size carefully balanced to

give optimum efficacy. Micronized Sulfur Fungicide can be

dusted or sprayed. It contains 95% micronized elemental

sulfur, which is produced as very small particles, ranging from





6 to 8 µm in size. Micronized Sulfur Fungicide also has insecticidal qualities. Micronized sulfur is

readily miscible in water and fumes at lower temperatures (72ÛF/22ÛC) than conventional

formulations. Do not apply micronized sulfur in temperatures over 80 degrees F or when the

temperatures are expected to exceed 85 degrees F within three days after application.

C olloidal sulfur

These are made up of smaller particles than can be produced by ordinary grinding

processes. They may be produced in several ways, generally by acidifying lime-sulfur solution or

similar reaction.

Dust sulfur

It is a specifically formulation of sulfur used to

control diseases on various plants.Dusts (D)are a very finely

ground mixture of the active ingredientcombined with talc,

clay, powdered nut hulls, or other such materials. They are

used dry; never mix them with water.

Flowable sulfur

It is a microfine sulfur formulation in aqueous

suspension form. Particle size average diameter not more than 5

micron via coulter counter measurement. It has strong adhesive

properties that will act as a sticker and deposit builder for other

spray materials .A flowable,or liquid,can be mixed with water

to form a suspension in a spray tank .

Lime-sulfur





A mixture of calcium polysulphides and calcium

thiosulphate is the product obtained by the combination of

lime with sulfur, is commonly used today to control a variety

of diseases such as plum pockets, black knot, black spot of

rose, and a number of raspberry diseases. It has been used

widely for more than 50 years and is still used forsome of the

common fruit diseases.lime-sulfur is used mainly as a

dormant spray. Plant damage caused by lime-sulfur is most severe during dry weather when

temperatures reach 80 degrees to 95 degrees F.

Varied proportions of lime and sulfur are mixed in water to get the lime-sulfur. One of such

formula is:

Rock lime 20Ibs

Sulfur 15Ibs

Water 50gallons

Disease C ontrol b y Inorganic Sulfur Fungicides

Both elemental sulfur and lime-sulfur have been widely used as fungicides for the control of

different types of diseases, particularly powdery mildew. Application of 114g of sulfur per squarem

area around the infected plant controlled the with root disease of replanted rubber. The sulfur

reduced the soil PH for a period up to 18 months. Reduced PH stimulated the activity of the

antagonistic microflora in soil as well as the growth of the pathogen (Rigidoporus lignosus) was also

affected by the lowered PH. Whereas elemental sulfur has been used as a residual fungicide, lime-

sulfur has been mainly used as a contact fungicide.

P h ytotoxicit y of Inorganic Sulfur Fungicides

Acute injury by sulfur is rare in temperate, but in warmer climates (above 80 f), severe

buring is sometime caused on cucurbits when sulfur is used for the powdery mildew control. Apples

treated with sulfur in semi-arid areas may develop lesions on the sun-exposed side of the fruit, an

injury attributed to "sulfur sun scald". Some of the fruit varieties are sulfur-sensitive. Among sulfur-

sensitive apple varieties are Stirling Castle AND Lane's Prince Albert.





Bordeaux M ixture

Bordeaux mixture is an important fungicide and can be easily prepared. This was first

discovered by Millardet in France in 1882 when he saw a paste of lime and copper sulphate had been

painted on vines by the roadside in the Bordeaux district. This paste of lime and copper sulphate was

originally intended to keep the local boys from stealing the fruits but Millardet realized that the

downy mildew which have been building up to disastrous levels in France was not attacking the

roadside vines.

Bordeaux mixture is prepared by mixing a slurry of lime in water into a solution of copper

sulphate in water. This is often done in the actual spray tank. Calcium carbide has been used as a

source of slurry, but explosion, probably initiated by cuprous acetylide, has occurred. The lime is

added in considerable molecular excess and the final product contains about 12.75 % of metallic

copper. It is very safe to use because of its low toxicity to animals and humans. The rather gelatinous

nature of fresh precipitate (and Bordeaux mixture should be made immediately before use) helps to

increase the deposit by delaying drainage from high-volume application. The carbonation of the

excess lime during exposure on the leaf probably assists the adhesion of the final deposit.

There have been developments in the copper and sulphur products made by the industry.

Bordeaux mixture is employed in several formulations. One such formulation is the 4:4:50 formula

which is done by mixing 4 lbs of copper sulphate, 4 lbs of lime and 50 U.S. gallons of water ± the

copper sulphate and lime solutions being prepared in separate containers before mixing.

Before mixing the lime and copper components of the mixture, one additional step (but an

important one) must be carried out. Each container of these materials should be strained through a

cheesecloth filter. If cheesecloth isn't available, use cloth of a similar loose weave. The filtering is

necessary to remove small pieces of lime or copper sulfate that won't dissolve; otherwise, you'll find

these tiny pieces in the end of your garden sprayer tip, clogging up the works!

To make the filter, simply place the cheesecloth loosely over the top of another container

and fix securely in place with a string or rubber band.

The filtered copper sulfate solution is added to a one-gallon container, followed by addition

of the filtered lime solution. Enough water (about 3 quarts) is then added to the container to bring the

total volume up to one-gallon.





Many plant pathologists consider that the original Bordeaux mixture made up in the field is

frequently found to be more effective in comparative tests and never less efficient than the more

convenient modern products.

ORGANIC FUNGICIDES

Compared to inorganic fungicides, organic fungicides have less environmental hazards.

These fungicides vary in compositions and include thiocarbamates, chlorinated phenols, and

carboximides. Sulphur, nitrogen, carbon, and hydrogen are important constituents of organic

fungicides.

Formalin

Also known as Formaldehyde, it is the first successful organic fungicide. Formaldehyde is a

colorless gas characterized by a pungent odor and has the chemical formula CH2O (also known as

Methanal). Commercial solutions of formaldehyde in water, commonly called formalin, were

formerly used as disinfectants and for preservation of biological specimens. Formalin is used as

fumigant for seeds, soil, and greenhouses because of its volatility.

Dithiocarbamates

These are commonly formulated as dusts, wettable powders, or water suspensions. They are

used to protect seeds, seedlings, turfs, ornamentals, vegetables, and fruits. Thiocarbamates includes

Metam-Sodium, Thiram, Ziram and Ferbam, Maneb, Zineb, Nabam, and Mancozeb.

A. M etam- Sodium

Metam-Sodium is formulated in aqueous solutions for applications as soil biocide

and fumigant to kill fungi, bacteria, weed seeds, nematodes and insects. Metam-Sodium can

be irritating to the skin. Poisonings by ingestion of metam-sodium has not been reported.

Although animal feeding studies do not indicate extraordinary toxicity of metam-sodium by

ingestion, its decomposition in water yields methyl isothiocyanate, a gas that is extremely

irritating to respiratory mucous membranes, to the eyes, and to the lungs. Inhalation of

methyl isothiocyanate may cause pulmonary edema (severe respiratory distress, coughing of

bloody, frothy sputum). For this reason, metam-sodium is considered a fumigant. It must be

used in outdoor settings only, and stringent precautions must be taken to avoid inhalation of

the evolved gas.





B . T hiram

Thiram is a common component of latex and possibly attributed to some allergies

attributed to latex. Thiram dust is moderately irritating to human skin, eyes, lungs, and

respiratory mucous membranes. Contact dermatitis has occurred to some occupationally

exposed workers. Systemic human poisonings by thiram itself have been very few, probably

due to limited absorption in most circumstances involving human exposure.

C . Z iram and Ferbam

These are formulated as flowable and wettable powders, used widely on fruit and

nut trees, apples, vegetables, and tobacco. Dust from these fungicides is irritating to the skin,

eyes, and respiratory tract. Prolonged inhalation of ziram is said to have caused visual and

neural disturbances,and, in a single case of poisoning, a fatal haemolytic reaction.

Theoretically, exposure to ziram or ferbam may predispose the individual to antabuse

reactions if alcohol is ingested after exposure. However, no such occurrences have been

reported.

D . M aneb, Z ineb, N abam, and M ancozeb (eth ylenebisdithiocarbamate compounds )

Maneb and zineb are formulated as wettable and flowable powders. Nabam is

provided as a soluble powder and in water solution. Mancozeb is a coordination product of

zinc ion and maneb. It is formulated as dust and as wettable and liquid flowable powders.

These fungicides cause irritation to the skin, respiratory tract, and eyes. Both maneb and

zineb have apparently been responsible for some cases of chronic skin diseases in occupationally

exposed workers, possible by sensitization.

Although marked adverse effects may follow injection of EBDC compounds into animals,

systemic toxicity by oral and dermal routes is generally low. Nabam exhibits the greatest toxicity,

probably due to its greater water solubility and absorb ability. Maneb is moderately soluble in water,

but mancozeb and zineb are essentially water insoluble. Absorption of the latter fungicides across

skin and mucous membranes is very limited. Systemic poisonings of humans have been extremely

rare.





MANUFACTURE PROCESS

1. REACTOR. The reactors are either made of steel or ceramics to prevent corrosion of the

lining or wall brought about by the chemical reactions. The raw materials in their designated

required weight and proportions enter the chemical reactor. Inside the reactor, the chemicals

are mixed and react to form the desired compound.

2. INTERMEDIATE STORAGE. The resulting compound from the first reactor are then

stored in the intermediate storage where they are kept to avoid contamination before entering

another reactor.

3. SCRUBBER. Scrubbers are a diverse group of air pollution control devices that can be used

to remove some particulates and/or gases from industrial exhaust streams. Fumes resulting

from the chemical reactions in the reactor leave the reactor and proceeds to the scrubber to

be cleaned before being released. Chemical applications are utilized to neutralize the gases

before it enters the atmosphere. Environmental laws mandates that the companies take to

consideration the environmental hazards that can be brought about by such waste products.





4. SECOND REACTOR. The compound stored in the intermediate storage is then passed to

another reactor for addition of other chemicals. Here, metal sulphates and binders are added

to the mixture to form slurry.

5. SLURRY WASH AND FILTRATION. The slurry is then passed to a slurry wash and

filter. This is done so that unwanted impurities such as metallic compounds which are not

part of the compound would be washed and removed. These impurities are discarded as

wastewater and suitable treatments are done to purify the wastewater. Some of the waste

water are recycled back to the reactor to mix with the preliminary compound, metal

sulphates and binders. Recycling is done not only to reduce cost production, but also, in

some cases, done to improve the quality of the slurry.

6. DRIER. The washed slurry is passed to the dryer where excess moisture are removed. Air

and fumes from this process are released from the slurry. These are then passed to the

cyclone collector while the dried product proceeds to the formulation and packaging process.





7. FORMULATION AND PACK AGING. Here, the dried product is

measured to the right commercial weight and proportions, and then

packaged. The packaging is a crucial step in preserving the life of the

chemical fungicide. Vacuum technology is used to seal the packaged

product so that reactions with the air might be avoided.

8. CYCLONE COLLECTOR. Air from the drier is collected in the cyclone collector. Air

collected in the cyclone collector is used to pump some air into the bags in the bagging

procedure.

9. BAGHOUSES. The packaged products are then passed to the bag houses. Packages of the

product are then collected and packed in bags for ease of shipment or transport. Air from the

cyclone collector is used to fill in a little amount of air to the bags in order to reduce stress in

the shipping process.





Herbicides

INTR ODUCTION

A herbicide, commonly known as a weedkiller, is a pesticide used to kill unwanted plants.

Selective herbicides kill certain targets while leaving the desired crop relatively unharmed. Some of

these act by interfering with the growth of the weed and are often based on plant hormones.

Herbicides used to clear waste ground are nonselective and kill every plant with which they come

into contact. Smaller quantities are used in forestry, pasture systems, and management of areas set

aside as wildlife habitat. Some plants produce natural

herbicides, such as the genus Juglans (walnuts), or the tree

of heaven; such action of natural herbicides, and other

related chemical interactions, is called allelopathy.

Herbicides are widely used in agriculture and in landscape

turf management. In the U.S., they account for about 70% of

all agricultural pesticide use.

HISTORY

Herbicides have been used since the early 1850¶s, when salt was spread to control

unwanted plants. Salt, copper sulphate, and the other early herbicides were non-selective. Selective

herbicides came into use in the 1940¶s with the development of 2,4-dichlorophenoxyacetic acid,

often abbreviated as 2,4-D. This herbicide is easy and inexpensive to manufacture, and kills many

broadleaf plants while leaving grasses unaffected. Its low cost has led to continued usage today. Like

other acid herbicides, current formulations utilize either an amine salt (usually triethyl amine) or

ester of the base compound. These are easier to handle than the acid.

The 1950¶s saw the introduction of the triazine family of herbicides, which includes atrazine,

which have current distinction of being the herbicide family of greatest concern regarding

groundwater contamination. Atrazine does not break down readily (within a few weeks) after being

applied to soils of above neutral pH. Under alkaline soil conditions atrazine may be carried into the

soil profile as far as the water table by soil water following rainfall causing the aforementioned

contamination. Atrazine is thus said to have carryover, a generally undesirable property for

herbicides.





In the 1960¶s and 1970¶s, a mixture of the herbicides 2,4-D and 2,4,5-T was widely used to

defoliate (cause leaves to fall off) trees and brush. During the Vietnam War, this mixture became

known by the military code name Agent Orange. United States forces sprayed it on the jungle

vegetation in Vietnam to expose enemy snipers. During the early 1970¶s, researchers found that

Agent Orange and all the other 2,4,5-T products contained a highly poisonous substance called

dioxin. Dioxin contamination was a possible health hazard to people and animals.

2,4D exhibits relatively poor selectivity, meaning that it causes stress to non-target plants. It

is also less effective against some broadleaf weeds, including sedges and many vinous plants. Many

other herbicides have been developed to address these limitations. During this time, atrazine was

introduced, which has the dubious distinction of being the herbicide of greatest concern for

groundwater contamination.

Glyphosate, which is nonselective, was introduced in the late 1980s but did not become popular until

the development of crop plants that were resistant to it. The pairing of the herbicide with the resistant

seed led to the consolidation of the seed and chemistry industry in the late 1990s.

HOW HER BICIDES WOR K

Herbicides are widely used in management of landscape turf and in agriculture. They are

used in total vegetation control (tvc) programs for maintenance of way for highways and railroads.

Relatively smaller quantities are used in forestry, pasture systems, and management of set-aside

areas for wildlife habitat. Herbicides are manufactured in the form of a powder or a liquid. They are

diluted in water and sprayed on growing weeds or on the soil. Many herbicides control weeds by

preventing weed seeds from sprouting. These herbicides are mixed into the soil before or at the same

time that the crops are planted, or applied to the soil surface before crops and weeds start to grow.

Some herbicides kill plants by hindering photosynthesis, the process by which plants convert carbon

dioxide and water into food. Others called growth regulator herbicide s, cause plants to die

prematurely by altering their growth patterns. Most growth regulator herbicides are applied after the

crop or weed appears above the soil surface.

TERMINOLOGY

Control is the destruction of unwanted weeds, or the damage of them to the point where

they are no longer competitive with the crop





Suppression is incomplete control still providing some economic benefit, such as reduced

competition with the crop

Crop Safety, for selective herbicides, is the relative absence of damage or stress to the crop.

Most selective herbicides cause some visible stress to crop plants.

CLASSIFICATION OF HER BICIDES

Herbicides can be grouped by chemical family, biological effect, and type of vegetation controlled. It

is impossible to make a rigid classification of herbicides. Frequently, a herbicide can fit into more

than one place in a classification depending on the purpose for which it is needed and the rate at

which it is used. Three of the major types of herbicides are discussed below.

T ime of Application

The terms pre- and post emergence are used to denote time of application of herbicides to

both the crops and the weeds. Many people prefer to use such terms solely with respect to the crop

but to avoid confusion, the stage of development of both the crop and the weeds should be stated.

Pre-plant incorporated herbicides are soil applied prior to planting and mechanically

incorporated into the soil. The objective for incorporation is to prevent dissipation through

photodecomposition and/or volatility. Examples are dinitramine, EPTC, and Trifluralin (for

manufacturing process, see flowcharts)

Pre-emergent herbicides are applied to the soil before the crop emerges and prevent

germination or early growth of weed seeds. Examples are atrazine, butachlor, and propachlor.

Post-emergent herbicides are applied after the crop has emerged. Examples are Glyphosate,

2,4-D, and Paraquat.

M ode of Action

Contact herbicides destroy only that plant tissue in contact with the chemical spray.

Generally, these are the fastest acting herbicides. They are ineffective on perennial plants that are

able to re-grow from roots or tubers.

Systemic herbicides are foliar-applied and are translocated through the plant and destroy a

greater amount of the plant tissue. They are capable of controlling perennial plants and may be

slower acting but ultimately more effective than contact herbicides.





Selectivit y

Selective herbicides kill only broad-leaved plants or only grasses.

Non-selective herbicides kill all plant material with which they come into contact.

Some major herbicides in use toda y

Glyphosate, a systemic nonselective herbicide used in no-till burndown and for weed

control in crops that are genetically modified to resist its effects.

Paraquat, a nonselective contact herbicide used for no-till burndown and in aerial

destruction of marijuana and coca plantings. More acutely toxic to people than any other herbicide in

widespread commercial use.

2,4-D, a broadleaf herbicide in the phenoxy group used in turf and in no-till field crop

production. Now mainly used in a blend with other herbicides that act as synergists.

Clopyralid, another phenoxy herbicide used mainly in turf, rangeland, and for control of

noxious thistles. Notorious for its ability to persist in compost.

Metoalachlor, a pre-emergent herbicide widely used for control of annual grasses in corn

and sorghum; has largely replaced atrazine for these uses.

Dicamba, a persistent broadleaf herbicide active in the soil, used in turf and field corn.

Picloram, a phenoxy herbicide mainly used to control unwanted trees in pastures and edges

of fields.

Atrazine, a triazine herbicide used in corn and sorghum for control of broadleaf weeds and

grasses.





MANUFACTURING PR OCESS

Trifluralin (Treflan)

The process begins by charging the nitrator with cycle acid and fuming nitric acid and heating it to

40ÛC. P-chlorobenzotrifluoride is then added for mononitration, maintaining the temperature at 40ÛC

during the course of 4 hours. The temperature is raised and held at 75ÛC over 4 hours then cooled.

The spent acid from mononitration process is settled out and drawn off then sent to waste treatment.

The next step is to charge the denitrator with 100% sulfuric acid, 20% oleum, and fuming nitric acid

then the temperature is raised to 120ÛC. It is then ran into the mononitrator, still at 120ÛC, over 6

hours and held at this temperature over the course of 4 hours for denitration to take effect. It is then

cooled to 20ÛC and settled. Solids from the denitrator are filtered in a closed Nutsch filter, running

the spent acid to cycle acid storage. Then it is washed with water, sending the wash water to waste.

Chloroform is then dissolved (from the recovery still) and then charged into the amination reactor

with water, soda ash, and dinitro derivative (in chloroform solution). The temperature at this stage is

adjusted to 45ÛC then the aminate with dipropylamine is added at 45ÛC to 50ÛC over 4 hours and

heated for 4 hours more at 45ÛC. The rest of the water is added then passed through a filter press and

decanter to a vacuum still, the salt-water layer going to waste. In the vacuum still, the chloroform is

distilled overhead (for recycle). Aromatic naphthalene and emulsifiers are finally added to the

desired formulation.

FLOWCHAR TS

General Process Flow Diagram for the manufacture of Treflan (Trifluralin)





Examples of Nitro-type pesticides: Trifluralin and atrazine

EQUIPMENT

1. Nitrator 2. Filter press





3. Decanter 4. Vacuum still

5. Amination reactor 6. Chemical storage tank

7. Condenser




Waste Treatment

Liquid Effluents

agrichemical industries

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