Agrochemicals and their effects
Agrochemical pesticides are very important in crop
protection. Intensive use of pesticides over the years has posed severe environmental
problems. They include contamination of soil and groundwater, reduced productivity,
development of pesticide resistance among the pests, etc. When pesticides are
applied to protect crop plants from pests and diseases, only about 15% of the
spray preparation hits the target. The rest is distributed in the surrounding
environment.
Various factors are known to influence leaching of
agrochemicals into groundwater. They include the amount of rainfall, soil drainage,
depth of water table, mobility of pesticides, soil texture, etc. It also
includes agronomic factors like riming, rate and method of pesticide
application, etc. Endosulfan is relatively less mobile, but found to be most
common pesticide of groundwater samples.
Pesticides in shallow groundwater are of particular concern. Several agrochemicals are also found contaminating food. They cause hazardous effects on humans, animals and crop plants. Over use of chemical fertilizers to increase yield also should be avoided.
Most of the agrochemicals are general poisons and not specific for a particular species of pest. Hence, they kill useful pollinators and microorganisms of the soil also. Such microbes include the nitrogen fixing bacteria and cyanobacteria which can be used as biofertilizers. Thus natural productivity of the soil is greatly affected. In general, the pests manage to survive and become more resistant to pesticides. Obviously to control such resistant pests greater amounts of pesticides are required which, in turn, increase their hazards. Many pesticides - especially organo-chlorines - are non-biodegradable. They persist in the environment. They pollute air, water, soil and enter food chains. Being lipophilic, they get deposited in fatty tissues of organisms creating serious problems. The deposition of pesticides in fatty tissues of the host is called bioaccumulation. They may pass to higher members of ecosystem through food chain. Thus they occur in increasing concentration in top members of food chain. This is called biomagnification or bioconcentration. Many pesticides are toxic in nature. The person who handles them in industries or in fields may suffer from skin diseases, blindness, respiratory diseases, nervous disorders, etc.
To avoid ill effects of agrochemicals, organic farming is now coming up. In organic farming, only bio-pesticides and bio-fertilizers are used.