Bioaccumulation Crisis: PCBs and Environmental Consequences

Polychlorinated biphenyls (PCBs) widely used for industrial and commercial purposes from 1929 to 1979, have had devastating consequences due to environmental exposure resulting from leaky equipment and illegal or improper dumping of PCB wastes. Research has shown that PCBs are carcinogenic and can adversely affect the immune, reproductive, endocrine, and nervous systems. In 1979, their production was banned in the US under the Toxic Substances Control Act of 1976.

PCBs are highly stable chemicals that do not readily break down in the environment. They are insoluble in water but soluble in fat tissue, leading to their accumulation in the body over extended periods of time. This makes them ideal for biological magnification, a process in which harmful substances become increasingly concentrated as they move up the food chain. Similar toxic substances that exhibit biological magnification include pesticides like DDT and heavy metals such as arsenic, mercury, and lead.

The Great Lakes provide a stark example of biological magnification, with PCB concentrations increasing dramatically as they move up the food chain: from phytoplankton (0.025 parts per million) to zooplankton (0.123 ppm) to smelt (1.04 ppm) to trout (4.83 ppm) to herring gull eggs (124 ppm), resulting in a magnification of almost 5,000 times.

The uncontrolled use of DDT led to a catastrophic decline in the population of bald eagles, peregrine falcons, and brown pelicans, as highlighted in Rachel Carson's book Silent Spring (1962), which ultimately led to the ban on DDT in the US in 1972. In Japan, the dumping of methylmercury by the Chisso Corporation into Minamata Bay from 1932 to 1968 resulted in severe nerve toxicity (known as Minamata disease), leading to nearly 1,800 documented human deaths, as the toxic substance accumulated in fish and shellfish consumed by local residents and their animals.

Throughout history, heavy metals, chemicals, and pesticides have infiltrated the food chain, leading to the devastating loss of wildlife due to the process of biological magnification.