Types of Chemical Pesticides
The word pesticide comes from Latin pestis, which means the destructive agent or plague. Pesticides are generally oily or waxy substances in the form of dust, granules, pallets, emulsified concentrates, aerosols, soluble powders, wettable powders etc.
Types of Chemical Pesticides
According to their chemical nature, pesticides can be classified in below categories:
Organochlorines
Organochlorines are very slowly decomposing chlorinated organic compounds, which are lipophilic (show much affinity for the fatty tissue of animals). Examples of Organochlorines are DDT, BHC, Aldrin, Endosulphan etc.
- DDT is the most famous chemical in the world and is oldest synthetic pesticide.
- Benzene hexachloride (BHC) also known as Lindane or Gammexane was used in agriculture and Pharma until its farm use was banned under the Stockholm convention on Persistent Organic Pollutants. However, it is still used in second-line pharmaceutical treatment for lice and scabies.
- Aldrin is applied to foundations of buildings to prevent termite. D
Organophosphates
Organophosphates are organic esters of phosphoric, thiophosphoric and other phosphoric, thiophosphoric and other phosphoric acids. Common examples are Malathion, Parathion, Fenitrothion etc.
Malathion is widely used in agriculture, residential landscaping, public recreation areas, and in public health pest control programs such as mosquito eradication. In some countries, it is the most commonly used organophosphate insecticide. Malathion / Organophosphates are harmful and of concern to both scientists and regulators because they work by irreversibly blocking an enzyme that’s critical to nerve function in both insects and humans. Thus, their effect is mostly visible on nervous system.
Carbamates
Carbamates are organic compounds derived from carbamic acid (NH2COOH). They are having structural resemblance with acetylcholine. Examples of Carbamates are Aldicarb (Temik), Carbofuran (Furadan), Carbaryl (Sevin), Ethienocarb, Fenobucarb, Oxamyl And Methomyl. These insecticides kill insects by reversibly inactivating the enzyme acetylcholinesterase.
Pyrethoids
Pyrethroids are synthetic derivatives of pyrethrin. Pyrethrin is obtained from a plant botanically called chrysanthemum cineraifolium. These compounds are the fastest growing groups of chemicals today. They are highly toxic and quite expensive.
Common example is Pyrethrin, which is a natural insecticide and least harmful of all. It is one of the insecticides based on learning how wild plants, especially tropical species produce chemical compounds that repel insects or inhibit their feeding. There are two major types of these compounds pyrethrins from wild chrysanthemum type plants and rotenoids produced by the roots of rain-forest legumes. Both types of compounds are biodegradable, effective in low doses, and cause little harm to higher animals such as birds and mammals, including humans.
Triazines
Triazines are a group of herbicides derived from urea. They are used for controlling weeds in tea, tobacco and cotton. Examples are simazine, atrazine etc.
Environmental Hazards of Pesticides
Pesticides increase the crop yield manifold because the insects which destroy crops in bulk are killed. Further, insecticides have helped to counter the various insects that function as dreadful diseases such as Malaria.
However, pesticides / insecticides are poisons which kill all biota irrespective of their benefits or harms to the crops or animals or humans. Since these pests also make food chain in the ecosystem, their elimination disturbs the entire ecosystem. Further, many of the pesticides are persistent organic pollutants, which enter into the food chain and keep bioaccumulating. If they are soluble in water, they cause water pollution.
Labelling of Pesticides
The pesticide packet are labelled using square divided into two triangles with color in lower triangle and word poison in upper triangle. This categorization is as follows:
