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Pesticides and their impact on Environment
B.S. Joia
Senior Entomologist (retired)
Punjab Agricultural University, Ludhiana – 141 004, India
bsjoia@gmail.com
Pesticides are biologically active substances designed to kill pests. Every year crops worth severa1 million rupees are destroyed by pests. Insect-borne diseases affect million of people and animals annually. Substantial amounts of pesticides are used in agriculture to prevent these losses.. Non-agricultural uses of pesticides include their application in parks, gardens, lawns, golf courses etc. Pesticides are also used in construction industry and house holds. Use of pesticides against insect pests of public health importance is also common.
In India, production of food grains registered a four fold increase from around 50 million tonnes in 1950-51 to more than 210 million tonnes in 2006-07. Apart from introduction of high yielding varieties/ hybrids, assured irrigation, liberal finances; agro-chemicals have contributed significantly for substantial increase of agricultural production. Among agro-chemicals, pesticides have played a major role through avoiding losses caused by pests in different crops. However, have we analysed at what environmental cost we have achieved it?
Presently, there are 217 pesticides registered for use in India under The Insecticide Act, 1968, with annual consumption of about 570 g a.i./ha. With geographical area of only about 2%, Punjab accounts for more than 16% of the total amount of pesticides used in the country.
There is no doubt that pesticides in agriculture overshadowed all other control technologies as a means of plant protection. However, pesticides have their drawback as well. If pesticides were not poisonous or harmful, then the question of their adverse effects would have been unimportant. But, in order to accomplish their purpose, these chemicals have to be toxic. Pesticides are biologically active substances, designed to kill pests by their toxic effects.
Some of main problems due to excessive and indiscriminate use of pesticides are:- presence of pesticide residues in food and feed commodities, contamination of air, water and soil, insecticide resistance in insect pests, insect resurgence, out break of secondary pests, killing of non-target organisms including natural enemies and pollinators, useful insects, birds, animals etc. Pesticides, after application may persist as residues on agricultural produce, air, soil, water etc. for varying period of time with potential to harm man and his environment. In addition there are occupational hazards and accidental/ intentional poisoning associated with pesticides as well. Careless handing of pesticides results in poisoning leading to illness or even death. Chronic effects of pesticides include, carcinogeneticity, reproductive effects, mutagenecity, teratogenicity, neurotoxic and neurobehavioral effects, delayed neurotoxicity, allergy and other immuno-regulatory disorders, lung and kidney damage etc.
Pesticides can adversely affect the various components of the environment.
Air: Pesticides can pollute air and affect its quality. Pesticide drift occurs when fine droplets of pesticide suspended in air are carried away by wind to other areas. Pesticides that are applied to crops can volatilize and may be blown by winds into nearby areas. Dust formulations of pesticides cause more pollution than other formulations. Aerial application results in more pollution than ground application.
Water: Pesticides pollute water bodies. Pesticides have also been detected in rain and ground water. There are several routes through which pesticides reach water. It may drift out of the intended area where it is sprayed, it may percolate or leach through soil, it may be carried to water as run off or it may be spilled accidentally or through neglect. Pesticides may also be carried to water by eroding soil. Factors that affect a pesticide’s ability to contaminate water includes its water solubility, the distance from an application site to a water body, weather conditions etc.
Soil: Substantial amounts of pesticides sprayed on crops find their way to soil. It is reported that hardy 1-2% of pesticides reach target pest and major portion get lodged in soil. Herbicides are directly applied to soil. Soil is considered as ultimate sink for pesticides. The impact of soil contamination may endure for decades and adversely affect the quality and productivity of soil. It affects soil micro-organisms,earthworm and other beneficial organisms and may result in development of resistance in soil inhabiting insect pests. The pesticides from soil may be picked up by subsequent crops as residues. Persistence of pesticides in soil depends upon several factors like soil organic matter, pH, micro-organism, moisture, temperature etc.
Non-target organisms: Pesticides can kill non-target organism like bees, pollinators, natural enemies of insect pest, birds and animals. The non-target insects which are present in the crop field during pesticide application can get direct exposure, while those visiting later may pick up residues from crop or suspended particles. Animals may be poisoned by pesticide residues on food after spraying. Poisoning from pesticides can travel up the food chain; for examples, birds can be harmed when they eat insects that have been exposed to pesticides. Some pesticides can bioaccumulate and harm species high in food chain. Similarly, birds eating poisoned insect will ingest pesticides. Some pesticides are applied in granular form, and bird and other wild life, may eat the granules, mistaking them for grains of food.
Residues: Whenever pesticides are used in any situation they are going to leave some residues. The nature and level of residues depends upon several factors. Pesticide residues in food and feed above the legally permitted levels i.e. Maximum Residue Limits (MRL) are certainly undesirable. Pesticide residues in agricultural commodities have a significant influence in the area of international trade as well. Commodities with pesticide residues above MRL may be rejected by the importing countries.
Although considerable amount of research work is being conducted on the development of non-chemical methods of pest control, yet the general consensus is that these methods have not reached a stage that they can entirely substitute chemicals pesticides. Nevertheless, the potential risks of pesticides can not be ignored. In the use of pesticides, we must therefore, be keenly aware of, concerned and knowledgeable about their effects on man's total environment. |
