Final answer:
Biomagnification refers to the increasing concentration of toxic substances in organisms at higher trophic levels of an ecosystem. DDT and PCBs are notable substances that undergo biomagnification, with the effects seen in apex consumers like birds suffering from eggshell thinning and other health issues.
Step-by-step explanation:
The process by which toxic substances become concentrated in the tissues of organisms at higher trophic levels is known as biomagnification. This phenomenon occurs when a nonbiodegradable substance passes from lower trophic levels (such as phytoplankton) to higher trophic levels (like fish, birds, and mammals) within an ecosystem, with each successive level experiencing a greater concentration of the substance.
An example of biomagnification is seen with the pesticide DDT in aquatic ecosystems. As each organism feeds on others in the lower trophic level, DDT concentrations increase, leading to significant environmental and health impacts. Consequently, higher organisms such as birds can accumulate enough DDT in their systems to cause a thinning of eggshells, which leads to egg breakage during nesting, ultimately affecting the bird populations negatively. Similarly, studies have shown that substances like PCBs (polychlorinated biphenyls) biomagnify in aquatic food chains, reaching their peak concentrations in the tissues of apex consumers like birds that feed on fish. As a result of such impacts, the use of certain substances that contribute to biomagnification, like DDT, has been banned in many countries to protect ecosystems and human health.