How Does Biological Magnification Occur?

Biological magnification, also known as biomagnification, occurs as a buildup of chemical contaminants in a food chain, accumulating over time. Substances like DDT or other persistent chemicals build up in the fat tissues of an organism and cause disruptions in the natural processes of an ecosystem.

Trophic Levels

• Every time energy in the form of food moves up a level on the food chain, known as a trophic level, it is 1/10th the value of the previous level. This is not true for chemicals in the flesh of organisms being consumed. When a predator animal consumes a contaminated organism, it receives nearly all of the chemical contaminant stored in its prey.

Persistent Chemicals

• Biomagnification only occurs when individual organisms die before a contaminant can be broken down or excreted. Chemicals like mercury, DDT and its biological derivative DDE, PCB lubricants and other chlorinated organic molecules remain in their manufactured chemical state, which is toxic to many organisms in high enough concentrations. Many persistent contaminants bind to certain types of tissue, preventing their excretion from an organism. For instance, most chlorine-based pesticides bind readily to fat tissues and heavy metals like mercury are stored in muscle tissue. Even after a chemical is banned from production, it may remain in the environment for decades. Biomagnification may begin to occur in noticeable levels long after a contaminant has been identified as hazardous and removed from production.

High-Risk Environments

• The buildup of toxins is especially prominent in food chains with long-lived top predators and organisms with high body-fat contents. In Arctic environments, top predators like whales and polar bears have relatively long lives compared to most of their prey, and they have high body fat to combat the extreme cold.

Toxicity

• Toxicity only occurs after biomagnification has increased the per-organism dosage. In small quantities, many chemicals are nontoxic to animals higher up on the food chain. Even the notorious pesticide DDT is harmless to most mammals, birds, and medium to large fish unless it is metabolized into its derivative DDE and biomagnified. After reaching high enough concentrations, chemical contaminants interfere with natural processes. For example, the thinning shells of eagle eggs were caused by large quantities of DDE that interfered with shell calcification.

Human Health

• Since humans are at the top of a great number of food chains, risks of biologically magnified contaminants are high. Fortunately, the ability to diversify our diet and choose foods with low contamination levels allows us to avoid many negative consequences. Marine environments often see high levels of contamination, so if you like to eat fish, try to eat small, short-lived fish. Organisms low on the fish food chain will not have accumulated as many toxins as large fish like tuna and swordfish. Always wash fruits and vegetables to remove pesticides that may be on the skins, and do some research on where your food comes from. Organic produce may be more expensive, but it is also less likely to pass on any chemical contaminants to the consumer.