This process is sometimes known as bioaccumulation. Some studies show a distinction between “biomagnification” and “bioaccumulation.” Magnification occurs as the substance transfers across levels of the food chain, while accumulation can and does occur within a specific level.
Basically, biomagnification is the accumulation or build-up of trace amounts of a substance, which are transferred through the food chain (from the smaller organisms to the larger ones). The result is that the traces build to larger amounts in the higher food-chain levels.
One of the examples of biomagnification that has resulted in significant changes in regulations is the presence of pesticides in living things. When these chemicals are applied to vegetation and are consumed by smaller animals, the chemicals are transferred to these animals in slightly larger concentrations. As these small organisms are consumed and the food moves up the chain, chemicals are biomagnified or accumulated. This can result in toxic levels of substances that were once traces in small organisms.
Keys to the completion of this process include: substance must not dissolve well in water; the chain of consumption must not be broken; the substance must break down slowly in natural environment.
One of the most important gems of knowledge about this process involves the fatty tissue in living things. Items that cannot be broken down and eliminated will accumulate in fatty tissue. The amount may actually increase as it moves up the food chain, gaining in amount from the tissue of various organisms.
Several studies show mercury to be one of the substances that exists in tiny amounts in water. But as fish and plants are consumed and the natural order of the food chain occurs, this mercury not only continues to exist, the amount builds up to toxic levels. (Some states have freshwater lake advisories that caution citizens to eat only small amounts of fish, for this very reason.)
In the ocean, larger fish and predatory birds that eat fish have shown high concentrations of mercury. The substance began in small concentrations in smaller fish and in ocean vegetation. The amount of mercury in a small fish may be a microscopic fraction of that found in a large predator.
Among the chemical substances that have shown a disturbing trend toward biomagnification are the previously mentioned DDT and mercury, polychlorinated biphenyls (PCBs) and arsenic. For the past 15 years, research has added various metals and other chemical substances to the “watch” list for accumulation and biomagnification.
Academic research and nature studies have shown that large, predatory birds such as eagles, hawks and falcons have made a significant comeback in population numbers since DDT was eliminated from the food chain. Since it is no longer applied to vegetation as a pesticide it does not accumulate or magnify in the food chain.
According to scientific literature the two substances that magnify in nature are lipophilic and accumulate in fatty tissue. Both do not dissolve or degrade easily. Scientists call these substance POPs (persistent organic pollutants). The truth about biomagnification and bioaccumulation is well established, though new evidence is being uncovered all the time.