Bioconcentration occurs when an organism has higher levels of a toxin than its surrounding environment, often seen in aquatic environments. It can lead to biomagnification, where toxin levels increase up the food chain. Bioconcentration factors can be used to express levels numerically, and high levels can lead to health problems. DDT is an example of a toxin that caused biomagnification and harm to bird species, leading to bans on the chemical.
Bioconcentration is a situation where 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 to the related “bioaccumulation”, which can refer to toxins and organisms found in a variety of environments. Bioconcentration is an area of interest to many environmental advocates and scientific researchers, as well as those responsible for policy formulation and new consumer product development.
In a classic example of bioconcentration, a fish living in a river contaminated with pharmaceutical waste could take in 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 where the fish’s body contains more hormones than the surrounding water. Researchers can use a concept known as a bioconcentration factor (BCF) to express bioconcentration levels numerically.
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 offspring, cancer, death or disease. In fish populations, for example, an increasing number of fish born with ambiguous genitalia have been identified in streams contaminated by pharmaceuticals.
Bioconcentration can also lead to a situation called biomagnification. In biomagnification, toxin levels increase the further up the food chain you go. For example, a toxin may be present in small levels in plants eaten by small fish. Fish have to eat a lot of plants to survive, thus developing a higher BCF. The larger fish species that eats the small fish has an even higher level of toxins in its body, and the bear that eats these fish, in turn, develops higher levels of toxins. The toxin can also be passed on to fish-eating birds, along with humans. Bioconcentration explains how flame retardants are found in the breasts of women around the world: These women did not consume these chemicals directly, they ingested them by eating organisms that had undergone biomagnification.
Bioconcentration and biomagnification explain why seemingly low levels of toxins can become a problem, because if an animal has difficulty 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 only appeared to be toxic to insects. However, over a prolonged period of time, biomagnification has appeared resulting in thin-shelled bird eggs, causing great damage to many bird species. This has led to widespread bans on the chemical.
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