Toxic materials in the food chain

Toxic materials are poisonous. Some quickly break down into harmless substances in the environment. Others are persistent and do not break down. Instead, they accumulate in the food chain and damage the organisms in it, especially the top predators. Mercury and DDT are two persistent toxic materials. Mercury Mercury compounds were used until quite recently to make insecticides (chemicals that kill the insects that damage crops) and special paints that stop barnacles growing on the hulls of ships. Unfortunately, when it gets into the food chain mercury damages the nervous systems and reproductive systems of mammals, including humans. The diagram shows how mercury can accumulate in the food chain. Tiny plankton in the sea absorb the mercury compounds. When the plankton are eaten by small fish, the mercury they contain stays in the fish. As the fish need to eat a lot of plankton, the concentration of mercury in them becomes higher than its concentration in the plankton. The larger fish eat many small fish, and in turn larger fish still, such as the tuna fish, eat many of them. In this way, the concentration of mercury in the tuna becomes large. As people who eat a large amount of contaminated tuna may become ill, mercury is now banned from many chemicals. DDT DDT is a banned insecticide, which accumulates in birds and causes weakness in the eggs they produce. Check your understanding by studying the animation.