Chemicals, pesticides and heavy metals move up the food chain, get into aquatic bodies and are eaten by organisms like fishes which are in turn eaten by hawks/eagles. This process where the chemical enters the food chain and increase in concentration with increasing trophic level is known as biological magnification.

Yes, this magnification level will be different at different trophic levels in the ecosystem. Taking an example of a food chain of Plant—Goat—Man.

Plant grows by consuming pesticides from soil and water. These pesticides pass from plants to goats when goats eat plant. Man is omnivore and when man eats goat meat, the pesticides get transferred from goats to human. The level of pesticides is lowest in plants and maximum in man because increase in accumulation of pesticide increases with increasing trophic level.