Several pesticides and other chemicals are used to protect our crops from diseases and pests. These chemicals are either washed down into the soil or into the water bodies. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up by aquatic plants and animals. This is one of the ways in which they enter the food chain. As these chemicals are not degradable, these get accumulated progressively at each trophic level. Since human beings occupy the top level in any food chain, the maximum concentration of these chemicals gets accumulated in our bodies. This phenomenon is known as biological magnification. This is the reason why our food grains such as wheat and rice, vegetables and fruits, and even meat, contain varying amounts of pesticide residues. They cannot always be removed by washing or other means. Thus, the use of several pesticides which results in excessive accumulation of pesticides in rivers or ponds is a matter of deep concern.