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140 Environ. Sci. & Engg. Vol. 6: Toxicology
1
State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry,
Chinese Academy of Sciences, Guangzhou 510640, China
2
Centre for Environmental Sciences, Ce ntral University of South Bihar, BIT Campus,
Patna-800014, Bihar, India.
* Corresponding author: E-mail: icyadav.bhu@gmail.com
7
Pesticides Classification and Its Impact on
Human and Environment
I
SHWAR
C
HANDR A
Y
ADAV1
*
AND
N
INGOMBAM
L
INTHOIN GAMBI
D
EVI2
ABSTRACT
Pesticides are substance or mixture of substance which differ in their physical,
chemical and identical properties from one to other. Hence, they are classified
based on these properties. Some pesticides are also categorized into various
classes depending on the needs. Presently, three most popular classifications
of pesticides which are widely used is classification based on the mode of
entry, pesticide function and the pest organism they kill, the chemical
composition of the pesticide. Based on toxicity of pesticides, WHO classified
them into four classes: extremely dangerous, highly dangerous, moderately
dangerous and slightly dangerous. Improper application of pesticides can
cause severe harmful effect to living system and the environment. Most
pesticides do not distinguish between pests and other similar incidental
lifeform and kill them all. The toxicity of insecticides to an organism is
usually expressed in terms of the LD
50
(lethal dose 50 percent) and LC
50
(50
percent lethal concentration).
Key words:Pests, Insecticides, Toxicity, Dangerous, Organochlorine.
1. INTRODUCTION
A pesticide is a substance or mixture of substances intended for preventing,
destroying, repelling, or lessening the damage of any pest
[1]
. The pest can
be insects, plant pathogens, weeds, mollusks, birds, mammals, fish,
141Pesticides Classification and Its Impact on Human and E nvironment
nematodes (roundworms) and microbes that compete with humans for food,
destroy property, spread or help carry or spread diseases or are seen as a
nuisance. The most common used pesticides include insecticides, herbicides,
fungicides and rodenticides. The other less well-known pesticides comprise
growth regulators, plant defoliants, surface disinfectants and some swimming
pool chemicals. Most commonly, pesticides are used in health sector and
agricultural crops
[2]
. They are useful in public health for killing vectors of
the disease, such as mosquitoes while, pests damaging agricultural crops
are killed by pesticides. Naturally, pesticides are potentially toxic to other
non-target organisms, including humans. Hence, it is necessary to use them
safely and dispose properly.
2. TOXICOLOGICAL CLASSIFICATION OF PESTICIDES
Pesticide is a common term that characterizes several classes of insecticides,
herbicides, fungicides, rodenticides, wood preservatives, garden chemicals
and household disinfectants that are used to either to kill or protect from
pests
[1]
. These pesticides differ in their physical, chemical and identical
properties from one class to other. Therefore, it is worthy to classify them
based their properties and study under their respective groups. Synthetic
pesticides are manmade chemicals, and do not occur in nature. They are
categorized into various classes depending on the needs. Presently, there
are three most popular method of pesticides classification suggested by
Drum
[3]
. These three popular methods of pesticides classes comprises:
(i) classification based on the mode of entry, (ii) classification based on
pesticide function and the pest organism they kill, and (iii) classification
based on the chemical composition of the pesticide
[3]
.
2.1. Classification Based on Mode of Entry
The ways pesticides come in contact with or enter the target are called
modes of entry. These include systemic, contact, stomach poisons, fumigants,
and repellents.
2.1.1. Systemic pesticides
Systemic pesticides are pesticides which are absorbed by plants or animals
and transfer to untreated tissues. Systemic herbicide moves through the
plant and can reach to untreated areas of leaves, stems or roots. They are
capable in killing of weeds with partial spray coverage. They can effectively
penetrate in the plant tissues and move through plant vascular system to
kill specific pests. Some systemic insecticides are also applied and move
through animals to control pests such as warble grubs, lice, or fleas. The
movement of pesticides in plant tissues may be unidirectional or
multidirectional. Some pesticides may only move in one direction either up
142 Environ. Sci. & Engg. Vol. 6: Toxicology
or down within the plant while other pesticides may only move upwards in
plants. If applied to the root zone, it will travel throughout the plant, but if
applied to the leaves it will not move throughout the plant. Furthermore,
few pesticides are considered locally systemic and move only to a short
distance in a plant from the point of contact. Examples of systemic pesticides
include 2, 4-Dichlorophenoxyacetic acid (2, 4-D) and glyphosate
[4]
.
2.1.2. Non-systemic (Contact) pesticides
The non-systemic pesticides are also called contact pesticides as it acts on
target pests when they come in contact. Pesticides must come into physical
contact with the pest to be effective. The pesticide enters the body of pests
via their epidermis upon contact and causes death by poisoning. These
pesticides do not necessarily penetrate the plant tissues and consequently
not transported through the plant vascular system. Examples of contact
pesticides are paraquat and diquat dibromide.
2.1.3. Stomach poisoning and stomach toxicants
Stomach poisoning pesticide enters the pest’s body through their mouth
and digestive system and causes death by poisoning. Stomach poisons are
acquired during feeding of pests, when they ingest the insecticide applied in
the leaves and other parts of the plant. Stomach toxicants may also enter
the body of insects through the mouth and digestive tract, where they are
absorbed into the insect’s body. This is more appropriate especially in vector
control including bacteria, or their toxins, applied to the water where filter-
feeding mosquito or black fly larvae will consume the poison. These
insecticides kill the vector by destroying the midgut (or stomach) of the
larvae. Example: Malathion.
2.1.4. Fumigants
Fumigants are such pesticides which acts or may kill the target pests by
producing vapor. These pesticides form poisonous gases when applied. These
pesticides in vapor form enter the body of pests via their tracheal system
(respiratory) through spiracles and causes death by poisoning. Some of their
active ingredients are liquids when packaged under high pressure but change
to gases when they are released. Other active ingredients are volatile liquids
when enclosed in an ordinary container and are not formulated under pressure.
Fumigants are used to remove stored product pests from fruits, vegetables
and grains. They are also very useful in controlling of pests in soil.
2.1.5. Repellents
Repellents do not kill but are distasteful enough to keep pests away from treated
areas/commodities. They also interfere with pest’s ability to locate crop.
143Pesticides Classification and Its Impact on Human and E nvironment
2.2. Classification Based on Pesticide Function and Pest
Organism They Kill
Under this method, pesticides are classified based on target pest’s organism
and pesticides are given specific names to reflect their activity. The group
names of these pesticides arise from the Latin word cide (meaning kill or
killer) that are used as suffix after corresponding name of pests they kill
(Table 1). Not necessarily, all pesticides end with word-cide. Some pesticides
are also classified according to their function. For examples: growth
regulators, which stimulate or retard the growth of pests; defoliants, which
cause plants to drop their leaves; desiccants, which speed the drying of
plants for mechanical harvest or cause insects to dry out and die; repellents
which repel pests; attractants, which attract pests, usually to a trap; and
chemosterilants, which sterilize pests.
Table 1: Pesticide classification by target pests (modified after Fishel
[5]
)
Type of pests Target pests/Function Example
Insecticides Kill insects and other arthropods Aldicarb
Fungicides Kill fungi (including blights, mildews, molds, Azoxystrobin
and rusts)
Bactericides Kill bacteria or acts against bacteria Copper complexes
Herbicides Kill weeds and other plants that grow where Atrazine
they are not wanted
Acaricides Kill mites that feed on plants and animals Bifenazate
Rodenticides Contr ol mice and othe r rodents Warfarin
Algaecides Control or kill growth of algae Copper sulfate
Larvicides Inhibits growth of larvae Methoprene
Repellents Repel pests by its taste or smell Methiocarb
Desiccants Act on plants by drying their tissues Boric acid
Ovicides Inhibits the growth of eggs of insects and mites Benzoxazin
Virucides Acts against viruses Scytovirin
Molluscicides Inhibit or kill mollusc’s i.e. snail’s usually Metaldehyde
disturbing growth of plants or cro ps
Nematicides Kill nematodes that act as parasites of plants Aldicarb
Avicides Kill birds Avitrol
Moth balls Stop any damage to clo ths by moth l arvae Dichloro benzene
or molds
Lampricides Target larvae of lampreys which are jawless Trifluromethyl
fish like vertebrates in the river nitrophenol
Piscic ides Ac t again st fish es Ro tenon e
Silvicides Acts against woody vegetation Tebuthiuron
Termiticides Kills termites Fipronil
Also, there are pesticides that control more than one class of pests and
may be considered in more than one pesticide class. Aldicarb, which is widely
used in Florida citrus production, may be considered an acaricide, insecticide,
or nematicide because it controls mites, insects, and nematodes, respectively.
Another common example is 2, 4-D, which is used as a herbicide for broadleaf
144 Environ. Sci. & Engg. Vol. 6: Toxicology
weed control, but it is a plant growth regulator at low rates. Attractants
and repellents are considered pesticides because of their use in pest control.
2.3. Classification Based on Chemical Composition of Pesticides
The most common and useful method of classifying pesticide is based on
their chemical composition and nature of active ingredients. It is such kind
of classification that gives the clue about the efficacy, physical and chemical
properties of the respective pesticides. The information on chemical and
physical characteristics of pesticides is very useful in determining the mode
of application, precautions that need to be taken during application and the
application rates. Based on chemical composition, pesticides are classified
into four main groups namely; organochlorines, organophosphorus,
carbamates and pyrethrin and pyrethroids
[4]
. The chemical based
classification of pesticides is rather complex. In general, modern pesticides
are organic chemicals. They include pesticides of both synthetic and plant
origin. However, some inorganic compound is also used as pesticides.
Insecticides are important pesticides that can be further classified into
several sub-classes. The sub-classification of insecticides is given in Fig. 1.
Fig. 1: Classification of insecticides
2.3.1. Organochlorine
Organochlorines pesticides (also known as chlorinated hydrocarbons) are
organic compounds attached with five or more chlorine atoms. They
145Pesticides Classification and Its Impact on Human and E nvironment
represent the one of the first group of pesticides ever synthesized and used
in agriculture and in public health. Most of them were widely used as
insecticides for the control of a wide range of insects, and they have a long-
term residual effect in the environment. These insecticides may disrupt
the nervous system of the insects leading to convulsions and paralysis
followed by eventual death. Most common examples of these pesticides
includes: DDT, lindane, endosulfan, aldrin, dieldrin and chlordane. Though,
the production and application of DDT was banned in most developed
countries including United States many years ago, it is still being used in
most tropical developing countries for vector control (particularly where
malaria occurs).
2.3.2. Organophosphates
Organophosphate pesticides are considered to be one of the broad spectrum
pesticides which control wide range of pests due to their multiple functions.
They are characterized with stomach poison, contact poison and fumigant
poison leading to nerve poisons. These pesticides are also biodegradable,
cause minimum environmental pollution and are slow pest resistance
[6]
.
Organophosphorus insecticides are more toxic to vertebrates and
invertebrates as cholinesterase inhibitors leading to a permanent overlay
of acetylcholine neurotransmitter across a synapse. As a result, nervous
impulses fail to move across the synapse causing a rapid twitching of
voluntary muscles, hence, leading to paralysis and death. Some of the widely
used organophosphorus insecticides include parathion, malathion, diaznon
and glyphosate.
2.3.3. Carbamates
Structurally, Carbamates are similar to organophosphates. However, they
differ in their origin. Organophosphates are derivatives of phosphoric acid,
while carbamates derived from carbamic acid. The working principal of
carbamate pesticides is similar to organophosphate pesticides by affecting
the transmission of nerve signals resulting in the death of the pest by
poisoning
[3]
. Sometimes, they are also used as stomach and contact poisons
as well as fumigant. They can be easily degraded under natural environment
with minimum environmental pollution. Some of the widely used
insecticides under this group include carbaryl, carbofuran, propoxur and
aminocarb.
2.3.4. Synthetic pyrethroids
Synthetic pyrethroid pesticides are group of organic pesticide that can be
synthesized by duplicating the structure of natural pyrethrins. Relatively,
they are more stable with longer residual effects than natural pyrethrins.
146 Environ. Sci. & Engg. Vol. 6: Toxicology
Pyrethrins are grinded to produce active components. The major active
components are pyrethrin I and pyrethrin II plus smaller amounts of the
related cinerins and jasmolins. Synthetic-pyrethroid pesticides are highly
toxic to insects and fish but slightly toxic to mammals and birds. Most of
synthetic insecticides are non-persistent, and got broken easily on exposure
to light. They are considered to be amongst the safest insecticides for use
in food. Cypermethrin and Permethrin are the most used synthetic-
pyrethroid pesticides.
2.4. Other Minor Classes of Pesticides
2.4.1. Classification based on mode of action
Based on mode of action, pesticides are classified as:
2.4.1.1. Physical poison
These classes of pesticides bring about killing of one insect by exerting a
physical effect. For example: Activated clay
2.4.1.2. Protoplasmic poison
These pesticides are responsible for precipitation of protein. Example of
this pesticide is Arsenicals
2.4.1.3. Respiratory poison
Respiratory poisons are chemicals which inactivate respiratory enzymes.
Example: Hydrogen cyanide
2.4.1.4. Nerve poison
Chemicals inhibit impulse conduction. Example: Malathion
2.4.1.5. Chitin inhibition
These classes of chemicals inhibit the chitin synthesis in pests. Example:
Diflubenzuron
2.4.2. Classification based on sources of origin
Pesticide is a chemical or biological substance that aims to destroy the
pests or prevent the damage caused by pests. Based on sources of origin,
pesticide may be classified into chemical pesticide and bio-pesticides. The
main benefits of using biological pesticides are host specificity. They act on
the target pest only and strongly linked organisms, whereas chemical
pesticides are usually of wide range which affects large group of non-target
organisms. Bio-pesticides are usually environmentally friendly as they are
less toxic, decomposed easily and required in small quantities. Chemical
147Pesticides Classification and Its Impact on Human and E nvironment
pesticides cause major environmental pollution as they are quite toxic and
not always biodegradable. Another important advantage of using bio-pesticide
is the fact that they are less susceptible to genetic modification in plant
populations. This confirms the little chance of pesticide resistance in pests,
which is hardly seen in case of chemical pesticides. Chemical pesticides are
further divided into organochlorine, organophosphate, carbamate and
pyrethroids and are discussed already in previous section. Bio-pesticides
group of pesticides derived from natural materials such as animal, plant
and microorganism (bacteria, viruses, fungi, and nematodes). They are
classified into three groups.
2.4.2.1. Microbial pesticides
The active ingredient in microbial pesticides is microorganism such as
bacterium, fungus or protozoan. These pesticides kill insects either by toxins
released by microbial organisms, or by infection by the organisms. Two
most common pesticides that fit within this group include the bacterial
toxin produced by Bacillus thuringiensis ( Bti), and the live bacteria, Bacillus
sphaericus (Bs). The mode of action generally is producing a protein that
binds to the larval gut receptor which starves the larvae. These two bacterial
toxins are used against mosquito larvae and black fly larvae. Most microbial
pesticides are more selective than biochemical pesticides.
2.4.2.2. Plant incorporated protectants
These groups of pesticides are produced by plants naturally. Also, the gene
necessary for production of pesticide is introduced into the plant through
genetic engineering. Hence, the pesticide then produced by such plant and
the genetic material introduced are together defined as plant incorporated
protectants (PIPs).
2.4.2.3. Biochemical pesticides
The third class is Biochemical pesticides which include natural materials
that have nontoxic mechanisms to control pests. Examples of Biochemical
pesticides are insect sex pheromones (act by interfering in mating), a range
of aromatic plant extracts (work by attracting insect pests into traps).
2.4.3. Based on range of target it kills
Under this method of classification, pesticides are classified into two groups
as broad spectrum pesticides and selective pesticides. Broad spectrum
pesticides are those pesticides that are meant to kill a wide range of pests
and other non-target organisms. They are nonselective and are often lethal
148 Environ. Sci. & Engg. Vol. 6: Toxicology
to reptiles, fish, pets and birds. Some examples of broad spectrum pesticides
are chlorpyrifos and chlordane. Selective pesticides on the other hand are
those pesticides which kill only a specific or group of pests leaving other
organisms unaffected or with a little effect. A good example of selective
pesticides is 2, 4-D which affects broad-leaved plants leaving the grassy
crops unaffected.
2.4.4. Based on types of pesticide formulation
Pesticide formulations are a mixture of the active ingredient (AI) and inert
ingredients. Active ingredients are chemicals that aimed to control target
pests, while inert ingredient (such as water, petroleum solvent, wetting
agents, spreaders, stickers, extenders) are the materials added to the AI to
make pesticide safer, more effective and easier to measure, mix and apply.
They are also more convenient in handling. One group of pesticide may be
mixed with another group of non-pesticides or used in combination to produce
such pesticides. One group of pesticides is combined with another group of
pesticides in such a way that the effectiveness of one pesticide increased
and will provide better protection against one pesticide compound. Also,
they are capable of controlling multiple pesticides in single dose of application.
Pesticide formulations can be divided into three main types: solids, liquids
or gases. Some formulations are ready for use while others need further
dilution with water or, a petroleum-based solvent, or air (as in air blast or
ULV applications) before they are applied. The most commonly used
formulations are listed under following headings:
2.4.4.1. Liquids
These formulations consist of concentrated oil solutions of technical grade
pesticides combined with an emulsifier added to permit further mixing with
water. Emulsifiers are detergent-like materials that allow the suspension
of very small oil droplets in water to form an emulsion. Emulsifiable
concentrates are used with water dilutions widely to control vector.
2.4.4.2. Powders
These dispersible powders are finely ground. Dry powders consisting of
active pesticide ingredients mixed with other ingredients to help in mixing
and dispersion. They are of two types: - wettable and soluble powder. Wettable
powders are designed for mixture with a liquid, usually water, for application
by spray equipment. They are generally mixed with water to form slurry
before being added to the spray tank, where they require continual agitation.
WPs can be used for most pest problems and in most spray equipment. Bti
is available as a WP. Soluble powders are similar to wettable powders,
except that the active ingredient, as well as the diluent and all formulating
149Pesticides Classification and Its Impact on Human and E nvironment
ingredients are completely soluble in water. Uses of soluble powders are
similar to those of wettable powders.
2.4.4.3. Granules
Under this formulation, the active ingredient is mixed with various inert
clays to form particles of various sizes. The size of granules used in vector
control usually ranges from 20 to 80 mesh. Granular formulations are
prepared for direct application and require specialized dispersal equipment.
They can be applied from the air or on the ground. They may be used with
small hand-cranked units, or simply scattered by hand (with appropriate
personal protection). Granular applications of pesticides are especially useful
in treating mosquito larvae in locations where heavy vegetation would
otherwise prevent the insecticide from reaching the water. They are also
favored in situations where drift would otherwise be a problem.
2.4.4.4. Baits
Baits contain active ingredients that are mixed with a pest food or attractant.
The main usages of baits include control of household pests such as ants,
mice, rats, roaches, and flies. They are also used outdoors to control birds,
ants, slugs, snails, and agricultural pests such as crickets and grasshoppers.
2.4.4.5. Dust
Dust pesticides formulations are finely ground mixtures of active ingredient
and a carrier material. Dust formulations are intended for direct application
without further mixing. Use of dusts are not suggested where drift is a
potential problem. For this reason, herbicides are not formulated as dusts.
In vector control, dusts are frequently used to control fleas and other eco-
parasites on pets. They are also applied to rodent burrows and bait stations
to control fleas in plague control operations.
2.4.4.6. Ultra low volume liquid
Ultra low volume concentrates (ULV) are sold as technical product in its
original liquid form, or solid product dissolved in a small amount of solvent.
These concentrates may approach 100% active ingredient. They are designed
to be used as is or to be diluted with only small quantities of specified
solvents. These special-purpose formulations are used in agricultural,
forestry, ornamental, and mosquito control programs. Larger droplets are
considered inefficient, wasteful, and can have undesirable environmental
effects. However, ULV applications, when done correctly, are very effective
and very safe to people and other non-target organisms.
150 Environ. Sci. & Engg. Vol. 6: Toxicology
2.4.5. Based on toxicity of pesticides
Depending on the health risk associated with pesticides and toxic behavior
of pesticides. The World Health Organization (WHO) classified them into
four categories
[7]
. WHO conducted an experiment on rats and other
laboratory animals by administering a dose of pesticide orally and dermally?
They then estimated the median lethal dose (LD
50
) that produces death in
50% of exposed animals to reach this conclusion. The ranking class from
lowest to highest toxicity in numbers I through IV indicates extremely toxic,
highly toxic, moderately toxic, slightly toxic, respectively (Table 2).
Table 2: WHO classifications of pesticides
[8]
WHO class Toxicity level LD
50
for the rat Examples
(mg/kg bod y weight)
Oral Dermal
Class Ia Extremely hazardous <5 <50 Parathion, Dieldrin
Class Ib Highly hazardous 5–50 50–200 Eldri n, Dichlorvos
Class II Moder ately hazardous 50–2000 200–2000 DDT, Chlordane
Class III Slightly hazardous >2000 >2000 Malathion
Class IV Unlikely to present acute 5000 Carbetamide,
hazard in normal use Cycloprothrin
3. EFFECT OF PESTICIDES
Despite beneficial results of using pesticides in agriculture and public health
sector, their use also invite deleterious environmental and public health
effects. Pesticides hold a unique position among environmental contaminants
due to their high biological activity and toxicity. Most pesticides do not
distinguish between pests and other similar incidental lifeform. They are
potentially harmful to humans, animals, other living organisms, and the
environment if used incorrectly. It is estimated that about 5000–20,000
people died and about 500,000 to 1 million people get poisoned every year
by pesticides
[9,2]
. At least half of the intoxicated and 75% of those who die
due to pesticide is agricultural workers. The rest is being poisoned due to
eating of contaminated food.
3.1. Potential Impact on Human Health
Pesticides may enter the human body through inhalation of polluted air,
dust and vapor that contain pesticides; through oral exposure by consuming
contaminated food and water; and through dermal exposure by direct contact
with pesticides
[10]
. Pesticides are sprayed onto food, especially fruits and
vegetables, they secrete into soils and groundwater which can end up in
drinking water and pesticide spray can drift and pollute the air. Toxicity of
chemicals, length and magnitude of exposure determines the degree of
151Pesticides Classification and Its Impact on Human and E nvironment
harmful impact on human health
[11]
. Toxicity of chemicals depends on the
nature of toxicant, routes of exposure (oral, dermal and inhalation), dose
and organism. Toxicity can be either acute or chronic. Acute toxicity is the
ability of a substance to cause harmful effects which develop rapidly following
absorption, i.e., a few hours or a day. Chronic toxicity is the ability of a
substance to cause adverse health effects resulting from long-term exposure
to a substance. Toxicity of insecticides commonly expressed in terms of
lethal dose 50% (LD
50
) or lethal concentration 50% (LC
50
). LD
50
is the single
exposure dose of the poison per unit weight of the organism required to kill
50% of the test population, where the population is genetically homogeneous.
It is expressed in milligram per kilogram body weight. LC
50
is the
concentration of the chemical in the external medium (usually air or water
surrounding experimental animals), which causes 50% mortality of the test
population, where the population is genetically homogeneous. It is expressed
in parts per million (ppm).
3.1.1. Acute effect
The harmful effects that occur from a single exposure by any route of entry
are termed “acute effects.” The four routes of exposure are dermal (skin),
inhalation (lungs), oral (mouth), and the eyes. Acute toxicity is determined
by examining the dermal toxicity, inhalation toxicity, and oral toxicity of
test animals. In addition, eye and skin irritation are also examined. Acute
illness generally appears a short time after contact or exposure to the
pesticide. Pesticide drift from agricultural fields, exposure to pesticides
during application and intentional or unintentional poisoning generally leads
to the acute illness in humans
[12,13]
. Several symptoms such as headaches,
body aches, skin rashes, poor concentration, nausea, dizziness, impaired
vision, cramps, panic attacks and in severe cases coma and death could
occur due to pesticide poisoning (Table 3). About 3 million cases of acute
poisoning due to pesticides are reported worldwide every year. Out of these
3 million pesticide poisoning cases, 2 million are suicide attempts and the
rest of these are occupational or accidental poisoning cases
[14]
.
3.1.2. Chronic effect
Any harmful effects that occur from small doses repeated over a period of
time are termed “chronic effects.” Suspected chronic effects from exposure
to certain pesticides include birth defects, toxicity to a fetus, and production
of benign or malignant tumors, genetic changes, blood disorders, nerve
disorders, endocrine disruption, and reproduction effects. The chronic
toxicity of a pesticide is more difficult than acute toxicity to determine
through laboratory analysis. Continued and repeated exposure to sub lethal
quantities of pesticides for a long period of time (may be several years to
decades), causes chronic illness in humans
[15]
. Symptoms are not
152 Environ. Sci. & Engg. Vol. 6: Toxicology
immediately noticed but appeared at a later stage. More commonly
agricultural farmer is at a higher risk to be affected. However, there is
equal chance of general population also to be affected especially due to
contaminated food and water or pesticides drift from the fields
[15]
. Recently
several studies establish a link between pesticides exposure and the
incidences of human chronic diseases affecting nervous, reproductive, renal,
cardiovascular, and respiratory systems
[16]
. Some of the most common
chronic diseases due to long exposure of pesticides are given in Table 4.
3.2. Impacts on Environment
Extensive application and subsequent disposal of pesticides by farmers,
institutions and the general public offer numerous possible sources of
pesticides in the environment. It is almost impossible to limit the area of
effect of pesticides. Even when it is applied in a very small area, it spreads
in the air, is absorbed in the soil or dissolves in the water and eventually
reaches a much bigger area. Pesticides once released into the environment
may have many different fates. When pesticides are sprayed in agricultural
crop, it may find their way through the air and eventually end up in other
segments of the environment, such as in soil or water. Pesticides that are
applied directly to the soil may be washed off and reaches to nearby surface
water bodies through surface runoff or may percolate through the soil to
lower soil layers and groundwater
[36]
. The effects of pesticides on
environmental system may range from minor deviation on the normal
functioning of the ecosystem to the loss of species diversity. Sometime, use
Table 3: General symptoms of pesticide poisoning
Mild poisoning Moderate poisoning Moderate poisoning
Any of the following: Any of the mild symptoms, Any of the mild symptoms,
plus any of the following: plus any of the following:
• Irritati on of the no se, • Vomiting • Inability to breathe
throat, eyes or skin
• Headache • Excessive salivation • Extra phlegm or mucous
in the airways
• Dizziness • Coughing • Small or pinpoint pupils
• Loss of appetite • Feeling of constriction in • Chemical burns on the skin
throat and che st
• Thirst • Abdominal cramps • Increased rate of breathing
• Nausea • Blurring of vision • Loss of reflexes
• Diarrhea • Rapid pulse • Uncontrollable muscular
twitching
• Sweating • Excessive perspiration • Unconsciousness
• Weakness or fatigue • Profound weakness • Death
• Restlessness • Trembling
• Nervousness • Muscular incoordination
• Changes in mo od • Mental confusion
• Insomnia
153Pesticides Classification and Its Impact on Human and E nvironment
of pesticides may cause long term residual effects while otherwise acute
fatal effects. For example, most organochlorine pesticides which are
persistent in the environment for long time, hence, resulting in
contamination of groundwater, surface water, food products, air and soil.
3.2.1. Impacts on non-target organism
Most insecticides once applied to kill pests; it may also adversely non-
target organisms such as earthworm, natural predators and pollinator
[37]
.
Pesticide applications can cause decline in earthworm populations. For
example, carbamate insecticides are very toxic to earthworms and some
organophosphates have been shown to reduce earthworm populations
[38]
.
Unfortunately, natural predator such as parasitoids and predators
(essential for controlling pest population level) are most susceptible to
insecticides and are severely affected
[39]
. The destruction of these natural
predators can exacerbate pest problems. Usually, if natural enemies are
absent, additional insecticide sprays are required to control the target
pest. Additionally, pesticides can also affect predator behavior and their
life history parameters including growth rate, development time and
other reproductive functions.
Pollinators such as bees, fruit flies, some beetles, and birds can be used
as bio-indicators of ecosystem processes in many ways as their activities
are affected by environmental stress caused by pesticides application and
habitat modifications
[40]
. Use of pesticide may also causes direct loss of insect
pollinators and indirect loss to crops because of the lack of adequate
populations of pollinators
[5]
.
Table 4: Common chronic diseases of pesticides
Diseases References
Cancer (Childhood and adult brain cancer; Lee et al.
[17]
; Shim et al.
[18]
; Heck et al.
[19]
;
Renal cell cancer; lymp hocytic leukemia Xu et al.
[20]
; Band et al.
[21]
; Cocco et al.
[22]
(CLL); Prostate Cancer)
Neuro dege ner ative diseases including Elbaz et al.
[23]
; Hayden et al.
[24]
; Tanner et
Parkinson disease, Alzheimer dise ase al.
[25]
Cardio-vascular disease including artery Abdullah et al.
[26]
; Andersen et al.
[27]
disease
Diabetes (Type 2 Diabete s) Son et al.
[28]
Reproductive disorders Petrelli and Mantovani
[29]
; Greenlee et al.
[30]
Birth defects Winchester et al.
[31]
; Mesnage et al.
[32]
Hormonal imbalances including infertility Xavier et al.
[33]
and breast pain
Respiratory disease s (Asthma, Chronic Chakraborty et al.
[34]
; Hoppin et al.
[35]
obstructive pulmonary disease (COPD))
154 Environ. Sci. & Engg. Vol. 6: Toxicology
3.2.2. Loss of biodiversity
Biodiversity is often considered as a measure of the healthy biological
systems. The more the number of organisms living in balances is an
environment, the healthier that environment is. A diverse environment
sustains many types of lifeforms all of which are interdependent. These
may range from microbes to insects such as ants, beetles and wasps to
birds to large animals such as the elephant and predators such as foxes,
wolves, wild dogs, lions, tigers and bears. Such a system has the ability to
maintain its balance so that no one species becomes dominant. Sometime,
pest may also be beneficial to biological system by consuming and controlling
other pests. Therefore, eliminating even single species by use of pesticide
can cause significant changes and may result in many others changes also
becoming extinct in that environment. In some case, a pesticide may
eliminate a species essential to the functioning of the entire community, or
it may promote the dominance of undesired species or it may simply decrease
the number and variety of species present in the community. This may
disrupt the dynamics of the food webs in the community by breaking the
existing dietary linkages between species.
3.2.3. Impacts on soil micro-flora
A major portion of the non-target pesticides from agriculture application
and other sources may accumulates in soil. Further, the indiscriminate
and repeated use of pesticides aggravates this soil accumulation. Soil
properties and soil microflora gets affected due to pesticides which may
undergoes a variety of degradation, transport, and adsorption/desorption
processes
[41]
. The degraded pesticides interact with the soil and with its
indigenous microorganisms, thus altering its microbial diversity, biochemical
reactions and enzymatic activity
[41,42]
. Any alteration in the microbial diversity
and soil biomass eventually leads to the disturbance in soil ecosystem and
loss of soil fertility. Pesticide application may also inhibit or kill certain
group of microorganisms and outnumber other groups by releasing them
from the competition
[41]
. They may also adversely affect the soils vital
biochemical reactions including nitrogen fixation, nitrification, and
ammonification by activating/deactivating specific soil microorganisms and/
or enzymes
[41,42 ]
. Pesticides have also been reported to influence
mineralization of soil organic matter, which is a key soil property that
determines the soil quality and productivity
3.2.4. Impacts on water and air ecosystem
Pesticide residues in water are a major concern as they pose a serious
threat to biological communities including humans. There are different
ways by which pesticides can get into water such as accidental spillage,
155Pesticides Classification and Its Impact on Human and E nvironment
industrial effluent, surface run off and transport from pesticide treated soils,
washing of spray equipment after spray operation, drift into ponds, lakes,
streams and river water, aerial spray to control water inhibiting pests
[14]
.
Pesticides generally move from fields to various water reservoirs by runoff
or in drainage induced by rain or irrigation
[43]
. Similarly, the presence of
pesticides in air can be caused by number of factors including spray drift,
volatilization from the treated surfaces, and aerial application of pesticides.
Extent of drift depends on: droplet size and wind speed. The rate of
volatilization is dependent on time after pesticide treatment, the surface
on which the pesticide settles the ambient temperature, humidity and wind
speed and the vapor pressure of the ingredients. The volatility or semi-
volatility nature of the pesticide compounds similarly constitutes an
important risk of atmospheric pollution of large cities
[44]
.
4. SUMMARY
Several groups of pesticides have been classified based on numerous criteria.
Most popular basis of pesticides classification are the nature of target pests
kill, chemical composition and characteristics of pesticides, mode of entry
and mode of action or the way a pesticide destroys or controls the target
pest. Pesticides with similar structures have similar characteristics and
usually have a similar mode of action. Most pesticide active ingredients are
either inorganic or organic pesticides. Pesticides have also been classified
according to how or when they work. It is seen that the in appropriate
application of pesticide may adversely affect all levels of biological
organization and every component of the environment. The effects can be
global or local, temporary or permanent, or short-lived (acute) or long-term
(chronic). The most serious effects involve destruction of non-target pest
organism (earthworm, pollinator and predators), loss in biological diversity,
microbial diversity, and soil biomass or community structure. These
ecological losses due to pesticides application are economically or socially
important. Hence, pesticides user especially farmer are suggested to reduce
the impacts of pesticides by minimizing their application or by replacing it
with bio-pesticides.
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