Food Chain/Web

Biomagnification (also called food web magnification or food web accumulation) is the progressive increase in the concentration of contaminants in organisms as the trophic level increases. This means lower trophic levels generally have smaller concentrations of contaminants than higher levels. This occurs because of the ecological inefficiency of food webs and persistent, hydrophobic contaminants bioaccumulating in organisms. These two factors mean that each trophic level has a larger concentration of contaminants dissolved in a smaller amount of biomass than the previous level. Each trophic level becomes more contaminated than those below it. For example, DDT in the Lake Ontario food web is biomagnified up the food web, so that top predators like herring gulls have tissue concentrations that are 630 times greater than primary consumers like zooplankton.

Dolphins have been studied by Japanese researchers as a model species for biomagnification because their migratory routes are known, they live in relatively unpolluted waters, and they live a long time (20-50 years). DDT has been found in dolphin blubber in greater concentrations (100 times greater than sardines) than would be expected given the small concentrations present in the water and in sardines, their favorite food. These unexpectedly large concentrations are the result of DDT biomagnification up the food web.

Biomagnification has serious consequences for all species. It is particularly dangerous for predator species especially if they are at the top of long food webs. Predators are usually at or near the top of their food web. This puts them at risk because the degree of biomagnification is high by the time it reaches their trophic level. Also, top predators usually consume large quantities of meat which has lots of fatty tissue and contaminants. Polar bears, humans, eagles, and dolphins are examples of top predators, and all of these organisms are vulnerable to the effects of biomagnification. Predators that consume large amounts of fish also have a high degree of risk because persistent hydrophobics are widely dispersed in aquatic food webs and are biomagnified in fish.