PESTICIDES

Pesticides are natural or synthetic agents which may be any substance or mixture of substances used to prevent, destroy or control any pest, including unwanted plants or animals or vectors of human disease or animal species that cause damage or otherwise interfere in the production, processing, storage, transport or marketing of food, agricultural products, wood and wood products or animal feeds or may be administered to animals for the control of insects, arachnids or other pests in or on their bodies.

Therefore, the purpose of pesticides is to destroy certain unwanted living organisms, as well as constituting a particular group of biocides that can reach a wide lethality.

These substances have been considered as potential mutagens because they contain ingredients to cause changes in deoxyribonucleic acid (DNA).

History of Pesticides

4500 years ago Elemental sulfur dusting as pesticide 4000 years ago Use of poisonous plants to control pest 15th century Toxic chemicals such as arsenic (As), mercury (Hg), and lead (Pb) were

used to kill pests 17th century Nicotine sulfate (extracted from tobacco leaves) used as insecticide 19th century Natural pesticides, pyrethrum (extracted from chrysanthemums), and

rotenone (extracted from roots of tropical vegetables) Until 1950s, Arsenic-based pesticides were dominant 1939 Paul Müller discovered insecticidal activity of DDT (organochlorines)

was dominant 1975 Organochlorines were replaced by organophosphates and carbamates.

Since then, pyrethrin compounds have become the dominant insecticide.

CHARACTERISTICS OF PESTICIDES

• A pesticide is a chemical used to kill unwanted organisms and hazardous to animals and humans. Some pesticides can cause nerve or liver damage, birth defects and even cancer.

• Pesticides contain two components into it 1) active as well as 2) inert ingredients. • All active ingredients are specified by name and percentage by weight on the label. The

active ingredients play main role for desired effect of the pesticide. Inert ingredients are generally mixed with the active ingredients to create the final product.

• These inert ingredients of the pesticides serve purposes including increasing the effectiveness of the active ingredients, making the pesticide easier to use or apply, or allowing several active ingredients to combine into a solution.

• The inert ingredients constitute ~99% of the final product. Just because these inert ingredients don’t specifically target the pest, it doesn’t mean that they aren’t equally toxic as the active ingredients.

• A pesticide should have following properties like:

1) effective against pests 2) stability 3) affordable 4) no biomagnification 5) toxicity 6) acute and chronic effects

CLASSIFICATION OF PESTICIDES

Pesticides are classified on the basis of various criteria such as toxicity (Hazardous effects), pest organism they kill and pesticide function, chemical composition, mode of entry, mode of action, how or when they work, formulations and the sources of origin.

CLASSIFICATION OF PESTICIDES BASED ON TOXICITY

The toxicity of a pesticide is its capacity to cause injury to a living system, may be a human body, or parts of the body (such as the lungs or the respiratory system); a pond, a forest and those creatures that live there. Depending on the pesticide dose and its exposure time to the living organisms, there are two different types of toxicity (1) acute and (2) chronic toxicity Acute Toxicity- It refers to how poisonous a pesticide is to a human, animal or plant after single short term exposure. A pesticide with a high acute toxicity is deadly even when a very small amount is absorbed. Acute toxicity may be measured as acute oral toxicity, acute dermal toxicity and acute inhalation toxicity. Chronic toxicity- It refers to the delayed poisonous effect from exposure to a pesticide. Chronic toxicity of pesticides concerns the general public as well as those working directly with pesticides because of potential exposure to pesticides on/in food products, water and the air. In consideration with only acute toxicity, According to WHO, pesticides are classified by acute oral and acute dermal toxicity using the estimated respective lethal dose LD50 (the pesticide dose that is required to kill half of the tested animals when entering the body by oral or dermal route).

According to chemical structure, pesticides are classified into different families ranging from organochlorines and organophosphorus to inorganic compounds.

Table 1. Classification of pesticides according to toxicity, expressed as LD50 (mg/Kg)

WHO has further revised Globally Harmonized System (GHS) classification of pesticide as shown in below given table

MODE OF ENTRY OF PESTICIDES

There are three specific ways through which pesticides may enter to your body.

A). Dermal Route

Wet, dry, or gaseous forms of pesticides can be absorbed through the skin. Oil or paste forms allow greater absorption than water-based pesticides. The eyes, eardrums, scalp and groin areas absorb pesticides more quickly than other areas on the body. Once they are absorbed through skin, pesticides enter the blood stream and are carried throughout the body.

B). Inhalation Route

Dusts, spray mist, or fumes can be drawn into lungs as one breathes. Inhalation can occur during the mixing, fumigating or spraying etc. The larger particles tend to stay on the surface of the throat and nasal passages but smaller particles can be inhaled directly into the lungs and enter the blood stream.

C). Oral Route

Pesticides can enter the body through the mouth (ingestion). This can occur when hands are not properly washed before eating, swallowing by mistake or purposefully. Ingested materials can be absorbed anywhere along the gastrointestinal tract (mainly by the small intestine). Once absorbed, they the blood stream and circulate throughout the body.

The toxicity of a pesticide depends on the qualities of exposed individual as different individual characteristics affect the person’s responds. Some examples of these individual qualities include:

• Health conditions: Individuals with poor health condition are more sensitive. • Age: youngest and oldest individuals tend to be most sensitive. • Gender/sex: Females are more sensitive. • Body size: the effect of a dose is closely related to body weight.

Classification of pesticides on the basis of pests they kill and pesticide function (Use)

Use of pesticides • Agriculture is the largest sector in terms of pesticides use, it consumes ~85% of world

production to control the pests. • 10% of the total pesticides used in public health activities to control vector-borne

diseases such as malaria, Chagas disease and dengue, among others. • Used to control rodents, in water purification and in eradicating crops whose end

products are illegal drugs. • Used to control pests in malls, buildings, airplanes, trains and boats.

NATURAL or BIOBASED INSECTICIDES/ PESTICIDES

Plant materials yield some of the most widely used pesticides and many of them, are being supplemented by the synthetic organic insecticides. The roots, steams, leaves, or flowers may be finely ground and used as such or active parts may be extracted and used either alone or with other toxicants and auxiliary materials. Nicotine, Rotenone, Pyrethrin’s are well known examples of natural insecticides.

Nicotine- Nicotine is a volatile alkaloid obtained by treating stems and damaged leaves with an aqueous solution of alkali followed by steam distillation. Since it is volatile in nature, most of the nicotine is converted to sulphate and sold as a 40 % nicotine solution. Nicotine solution has successfully been applied against aphides, leafhoppers and thrips. It has also been employed as a fumigant.

Pyrethrin’s: Flowers of the pyrethrum plant contain toxic, non-nitrogenous organic ester, called pyrethrin’s. The powder of pyrethrin’s used against flies and non-toxics to man.

Rotenone: It is obtained as a poisonous principal from the roots of derris plants (leguminous plants) and other tropical and subtropical plants. It may be obtained by the extraction of ground derris with CHCl3 or CCl4. The solvent is removed and residue is dissolved in acetone. They are used as fish and effective stomach and contact poisons.

SYNTHETIC INSECTICIDES/ PESTICIDES

The use of synthetic pesticides began in the US in the 1930s and became widespread after World War II. By 1950, pesticide was found to increase farm yield far beyond pre-World War II.

Farmers depend heavily on synthetic pesticides to control insects in their crops. Today, it is one of the most commonly used methods in controlling insects.

In 1997, US pesticide purchase accounted for nearly one-third of the world market. Annual pesticide expenditure totaled approximately $11.9 billion. Two-thirds of pesticide purchased is used in agriculture.

The use of synthetic pesticides in agriculture comes with a cost for the environment, and the health of animals and humans.

There are many classes of synthetic pesticides based on their chemical structures. The main classes consist of organochlorines, organophosphates (esters of phosphoric acids), carbamates (derived from cabamic acid), and pyrethroids. Exposure to pesticides can cause acute (short term) or chronic (long term) effects on animals and humans beings, especially in the reproductive, endocrine, and central nervous systems.

Class Examples Area of Effect

Organochlorines DDT, Gammaxene, dieldrin, aldrin Reproductive, nervous, endocrine, and immune system

Organophosphates Malathion, Parathion, Diazinon, Glyphosate, Chlorpyrifos Central nervous system

Carbamates Carbofuran, carbaryl Central nervous system

Pyrethroids Fenpropanthrin, deltamethrin, cypermethrin Poorly understood

Today, there are more than 500 species of insects and mites that are resistant to some form of pesticides. As a result of the increasing resistance, countries have started to apply more products, combine pesticides, increase applications, or substitute with more toxic replacements.

BENEFITS AND ADVERSE EFFECTS OF PESTICIDES

As global population is growing continuously day by day, while agricultural land and other resources are limited. In such cases worlds is in regular demand for affordable quality foods. When it comes to agriculture and the need to meet our world’s growing needs. Pesticide use is often a topic of controversy. In simple line, pesticides greatly assist pest control. In the long term, however, pesticides appear to harm the health of humans and the environment at the same time. Whether you’re a decision maker in the agricultural industry or a consumer, it is important to weigh the pros and cons of pesticide use.

• A pesticide is any substance or mixture of substances whose purpose is to prevent, extinguish, or repel pests or to regulate plants. There are considerable benefits to pesticide use.

• Cooper & Hans summarize these benefits as primary and secondary. Primary benefits include improved crop and livestock quality and yields. Secondary benefits are less

immediate, and they include food security, increased export revenues, and reduced international spread of disease.

• In the short-range, pesticides reduce waste of crops, land, water, time, and other valuable resources.

DISADVANTAGES/ SIDE EFFECTS OF PESTICIDES.

• Domestic animal contaminations and deaths, loss of natural antagonists to pests. • Pollinator decline, losses to adjacent crops, fishery and bird losses. • Loss of soil fertility due to damage of some useful soil microorganisms due to pesticides. • Pesticides induce immunotoxicity in human beings and results immunosuppression,

hypersensitivity (allergies), autoimmune diseases, teratogenic effects, inflammation etc. • Peoples regularly with pesticides, such as farmers and workers of pesticide

manufacturing industries, are at high risk of cancer. Thousands of non-lethal poisonings and cancer cases each year are attributable to pesticides.

• Ground water/ water pollution. • Pesticide resistance in crops due to overuse.