Biomagnified pollutants are pollutants which become more concentrated as they move up the food chain, becoming much more intensified at higher levels of the food chain than they are towards the bottom. Several studies have suggested that a number of chemicals have a tendency to biomagnify, including some chemicals which were previously believed to be safe. In addition to being a threat to the welfare of the environment, biomagnification also poses a risk to people, particularly people who consume animal products.
Biomagnification is closely related to the concept of bioaccumulation, which refers to the buildup of a pollutant in a particular organism. Toxins bioaccumulate for a variety of reasons. They tend to be less water soluble, making it harder for the organism to flush them out, and they may attach to fat cells, building up in the tissues of the organism. Bioaccumulation can be deadly for a single animal, but it can also contribute to biomagnification.
In a classic example of biomagnification, microorganisms in the ocean are exposed to pollutants, and the fish which eat them also ingest these pollutants. Larger fish eat the smaller fish, and the larger fish are eaten by seals. At every step of the way, the concentration of the pollutant becomes ever higher, representing the pollution passed on from dozens or hundreds of animals. When a polar bear eats the seal, the biomagnified pollutants will build up to unprecedented levels in the body of the polar bear, causing the polar to get sick, pass on genetic abnormalities to its children, or die.
One of the big problems with biomagnified pollutants is that it can be difficult to identify them until they have reached the higher levels of the food chain. In the polar bear example above, it may take decades for the pollutants to manifest in the polar bear population, by which time it is too late to take steps to reduce their prevalence in the atmosphere and ocean. Scientists can determine that biomagnified pollutants are making the polar bear sick, but they cannot take substantial action to prevent more polar bears from getting sick, beyond restricting the distribution of the pollutant in the hopes that it will eventually work its way out of the food chain.
The issue of biomagnified pollutants is of special concern to regulatory agencies, because these agencies must think about the impact of pollutants not only on individual organisms, but on the food chain as a whole. If a chemical is approved for the market and it later turns up as a biomagnified pollutant in scientific research, this can reflect poorly on the regulatory organizations which are supposed to protect the environment.