Some metallic pollutants and pesticides are non biodegradable. These poisonous substances are not easily broken down in the body; instead they accumulate in the tissues. As they are consumed by higher trophic levels through the food chain their concentration keeps on increasing. This phenomenon is referred to as biomagnification. The permissible safe limit of DDT in human body is 0.2 ppm whereas it is found on an average human body contains 11 ppm of DDT.