Bioaccumulation and Biomagnification: Toxins Up the Food Chain

0:00A lake holds only a tiny trace of a toxin, a poisonous substance. Can that really harm its animals?

0:08Some toxins, like the pesticide DDT and the metal mercury, are hard for bodies to break down or get rid of.

0:17Here is a food chain in the lake: plankton, small fish, large fish, and an osprey, a bird that hunts fish.

0:25Plankton, tiny living things that drift in water, take in the toxin from the water.

0:32A small fish eats plankton day after day, and the toxin stays in its body, often stored in fat.

0:40So the toxin builds up over the fish's life. This is called bioaccumulation.

0:47A large fish eats many small fish, and keeps the toxin from all of them.

0:52An osprey eats many large fish, so it collects even more toxin.

0:58So at each step up the food chain, the toxin gets more concentrated, with more in each gram of body. This is called biomagnification.

1:08DDT made the eggshells of ospreys, eagles and falcons so thin that many broke before hatching.

1:16Many countries banned DDT in the 1970s, and these birds have since recovered in many places.

1:23Mercury builds up the same way, so large predatory fish such as tuna carry more mercury than small fish.

1:31So yes, a tiny trace in the water can become a harmful amount at the top of the food chain.

1:38Toxins that bodies cannot easily remove build up in each organism and concentrate up the food chain.