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Pesticides not only kill the pests but also a large variety of living things, including humans, they may be persistent or non-persistent pesticides once applied are effective for a long time. However as they do not break down easily they tend to accumulate in the soil and in the bodies of animals in the food chain.
For example: DDT, one of the first synthetic organic insecticides to be used, was thought o be the perfect insecticide. During the first ten years of its use (1942-1952), DDT is estimated to have saved about five million lives primarily because of its use to control disease-carrying mosquitoes. However after a period of use, many mosquitoes and insects became tolerant to DDT, thus making it lose its effectiveness. In temperate regions, DDT has a half-life (the amount of time required for half of the chemical to decompose) of 10 – 15 years. This means that if 100kg of DDT varies according to the soil type, temperature, kind of soil organisms present, and other factors. In tropical parts of the world, the half-life may be as short as 6 months. The use of DDT has been banned in some countries. However, India still permits the use of DDT, although only for purposes of mosquito control. Persistent pesticides become attached to small soil particles which are easily moved by wind and water to different parts thus affecting soils elsewhere. Persistent pesticides may also accumulate in the bodies of animals, and over a period of time increase in concentration if the animal is unable to flush them out of its system, thus leading to the phenomenon called “bioaccumulation”.
When an affected animal is eaten by another carnivore, these pesticides are further concentrated in the body of he carnivore. This phenomenon of acquiring increasing levels of a substance in the bodies of higher trophic level organisms is known as “biomagnifications”. This process, especially in the case of insecticides like DDT, has been proved to be disastrous. DDT is a well-known case of biomagnifications in ecosystems.
Other problems associated with insecticides are the ability of insect population to become resistant to them, thus rendering them useless in a couple of generations. Most pesticides kill beneficial as well as pest species increase rapidly following the use of pesticides as there are no natural checks to their population growth. The short-term and the long-term health effects to the person using the pesticide and the public that consumes the food grown by using the pesticides are also major concerns. Exposure to small quantities of pesticides over several years can cause mutations, produce cancers, etc.
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