Accumulation of no-biodegradable toxic substances in the body of the organisms at various trophic levels of the food chain and interrupting it is called as biomagnification.
For example, DDT is the most commonly known pesticide. DDT is helpful in killing pests like mosquitoes, fleas, house flies and bugs. On a long run, DDT has proven to be harmful to both man and environment.
*DDT sprayed in farms get settled in the soil. It percolated into the deep layers of the soil with water used in irrigating the field. Slowly, it reaches ground water.
*When the agriculture waste is dumped into water bodies, DDT enters water resources.
* It is absorbed by aquatic organisms like small planktons.
*When these planktons are consumd by fish, DDT gets aaccumulated in the body of fishes that feed on them.
*Fishes in turn pass on DDT to the birds that prey on it. In birds, DDT prevents formation of egg shell, leading to breaking of eggs even before they can hatch. Ultimately, the organisms which occupy the highest trophic level suffer the most.