Bioaccumulation

Bioaccumulation or biomagnification is the process by which contamination of the environment by persistent chemicals, including endocrine disrupters and other toxicants, leads to the accumulation of these chemicals by an entire ecosystem. For example, aquatic contamination by organochlorines and other toxicants leads to the subsequent accumulation of these chemicals by small aquatic wildlife. As these contaminated animals fall prey to carnivorous fish, birds and larger animals, the concentrations of the toxicants are progressively magnified in each predator. Humans who rely on meat taken from these animals will also be subject to biomagnification of these toxicants and may suffer detrimental health effects as a result of this exposure. Contamination of other ecosystems including soil, air and plants can similarly lead to the bioaccumulation of environmental contaminants.

Not all toxicants, including those suspected of endocrine disruption, are prone to bioaccumulation. Chemicals that are stable in the environment, with relatively long half-lives pose the greatest threat for bioaccumulation within ecosystems. Not only must chemicals be stable in the environment, but chemicals must also be fairly resistant to metabolism once inside the organism. Chemicals that are lipophilic (fat soluble) can be stored in fat deposits for many years inside the organism. It is these chemicals that are persistent, stable and lipophilic that may be bioaccumulated by animals and eventually humans.

Depicted here is a representation of bioaccumulation in a Northern ecosystem. Northern populations may be uniquely susceptible to bioaccumulation of certain toxicants because of their culture, lifestyle and diet. Diets high in animal fats, particularly meat and blubber from seal, walrus, whale as well as fish and birds may contribute to the accumulation of chemicals such as organochlorines in humans. In women, organochlorines derived from the diet are accumulated in fat stores and are subsequently secreted in breast milk and fed to nursing infants. There are many studies examining the accumulation of persistent chemicals (organochlorines, lead, mercury) by Northern populations. Detectable levels of many chemicals have been found in breast milk, serum, hair and fingernails. These studies have led to the development of health advisories which, through alterations of dietary practices, hope to reduce the levels of chemical contamination in humans.