Bioconcentration is a situation in which the levels of a toxin in an organism exceed the levels of that toxin in the surrounding environment. This term is often used specifically in reference to aquatic environments and aquatic organisms, in contrast with the related “bioaccumulation,” which can refer to toxins and organisms found in a variety of environments. Bioconcentration is an area of concern for many environmental advocates and scientific researchers as well as people responsible for formulating policy and developing new consumer products.
In a classic example of bioconcentration, a fish living in a river contaminated by pharmaceutical waste might intake high levels of human hormones from the water. If the fish cannot express the hormones, they build up in the body, leading to a situation in which the body of the fish contains more hormones than the surrounding water. Researchers may use a concept known as the bioconcentration factor (BCF) to express bioconcentration levels in a numeric way.
To find the bioconcentration factor, the levels of a toxin in an organism are divided by the levels in the surrounding water to find a ratio. The higher the ratio, the more severe the bioconcentration. A high BCF can lead to health problems such as genetic mutations passed on to descendants, cancers, death, or disease. In fish populations, for example, increasing numbers of fish born with ambiguous genitalia have been identified in waterways contaminated with pharmaceuticals.
Bioconcentration can also lead to a situation called biomagnification. In biomagnification, levels of toxins increase the higher one moves up the food chain. For example, a toxin may be present in small levels in plants which are eaten by small fish. The fish have to eat a lot of plants to survive, thus developing a higher BCF. The larger fish species which eats the small fish has an even higher level of toxins in its body, and the bear which eats these fish, in turn, develops high levels of toxins. The toxin may also be passed to birds which eat the fish, along with humans. Bioconcentration explains how flame retardants are found in the breasts of women around the world: these women did not directly consume these chemicals, they ingested them by eating organisms which experienced biomagnification.
Bioconcentration and biomagnification explain why seemingly low levels of toxins can become a problem, because if an animal has trouble expressing a toxin from its body, the toxin will build up as long as the organism is exposed. The chemical DDT is often cited as an example; when it was initially used, it appeared to only be toxic to insects. However, over a prolonged period of time, biomagnification resulting in thin-shelled bird eggs appeared, causing severe damage to many bird species. This led to widespread bans on the chemical.
