What is Bioaccumulation & Biomagnification? (DP IB Environmental Systems & Societies (ESS))

Bioaccumulation & Biomagnification

• Bioaccumulation is the build-up of persistent or non-biodegradable pollutants within an organism or trophic level because they cannot be broken down

  • This means that organisms at higher trophic levels (such as top predators) may accumulate higher concentrations of pollutants than those at lower trophic levels

• Biomagnification is the increase in the concentration of persistent or non-biodegradable pollutants along a food chain

  • As pollutants are passed up the food chain from one trophic level to the next, they can become more concentrated due to the decrease in total biomass of organisms at higher trophic levels

• Toxins such as DDT (dichlorodiphenyltrichloroethane) are persistent pollutants that can accumulate along food chains

  • DDT was a widely used insecticide in the mid-20th century that was found to have harmful effects on birds of prey such as eagles and falcons

  • When DDT was sprayed on crops, it would leach into waterways and eventually enter freshwater and marine ecosystems

  • DDT would then enter food chains (via plankton) and accumulate in the bodies of fish 

  • These fish would then be eaten by birds, which would accumulate higher concentrations of DDT

  • Because DDT is persistent and does not break down easily, it can continue to accumulate in the bodies of animals at higher trophic levels, leading to harmful effects such as thinning of eggshells and reduced reproductive success

Through the process of biomagnification, the concentration of DDT in the tissues of organisms increases at successively higher trophic levels in a food chain

• Mercury is another example of a pollutant that can accumulate along food chains

• Mercury is released into the environment through activities such as coal-fired power plants and gold mining

• Once in the environment, mercury can be converted into a highly toxic form called methylmercury, which can accumulate in the bodies of fish

• As larger fish eat smaller fish, the concentration of methylmercury within the tissues of these fish increases, leading to potential harm for humans who eat large predatory fish such as tuna or swordfish

• In 1956, for example, a chemical factory released toxic methylmercury into waste water entering Minamata Bay in Japan

  • Mercury accumulation in fish and shellfish caused mercury poisoning in local people (who ate the fish and shellfish) and resulted in severe symptoms (paralysis, death, or birth defects in newborns)

Biomagnification and bioaccumulation of a pesticide in an aquatic ecosystem