A substance is said to bioaccumulate when it is unable to be expressed by an organism, meaning that it becomes concentrated in the body. The term is usually used to refer to toxins, although other substances which are sometimes beneficial have also been known to bioaccumulate. Usually, however, the term is used to indicate a potential danger. A bioaccumulative substance is a material which has a tendency to bioaccumulate in the body.
A substance will bioaccumulate when the body is unable to process it, meaning that it is not expelled through sweat, urine, and other means. As the organism continues to be exposed to the substance, the overall concentration in the body rises. In the case of a heavy metal like mercury, this can lead to serious health problems. Other theoretically harmless substances can be dangerous when they bioaccumulate in the body.
Most typically, the fat of the body harbors bioaccumulative substances. When the fat is burned for energy, the toxins are released into the body. Some materials bioaccumulate in other parts of the body, such as the bone. Depending on the substance, health problems may occur years after the exposure, making it difficult to pinpoint the cause of the problems. This is often the case with cancers as a result of environmental exposure. Sometimes, it is impossible to determine what the cause of the cancer was, making it difficult to initiate environmental cleanup in a potentially toxic area, or to determine whether or not family members are at risk as well.
Many workplace illnesses are the result of bioaccumulation. Someone who is exposed to the same substance day after day in small concentrations may build up enough of the substance in the body to get sick. Another classic illustration of bioaccumulation is the rising level of mercury in fish around the world, or the DDT poisoning of birds. Bioaccumulation has become a huge environmental issue due to pollution and human activity which have greatly increased the amount of bioaccumulative substances in the environment.
A related concept is biomagnification. In biomagnification, the toxic substance is passed up the food chain, resulting in a more widespread environmental problem. For example, fish absorb mercury through feeding in contaminated waters. When fish bioaccumulate mercury, other animals, including humans, are exposed to the toxic substance through consumption of fish. Thus, mercury can bioaccumulate in multiple species, creating a potentially very serious problem.