Seafood species can contain trace amounts of a variety of different chemicals. Mercury and Polychlorinated Biphenyls (PCBs) are two commonly studied seafood contaminants that are believed to be particularly harmful for pregnant or nursing women and children. While the study of toxicity in humans is incredibly complex, studies indicate that early exposure can lead to serious adverse health effects.
Mercury
Mercury is a toxin that causes a wide range of harmful health effects in humans. It can impact the central nervous system, kidneys, and immune system, and, in particular, brain development. Mercury is present as organic and inorganic forms in the environment from both man made and natural sources. The degree of toxicity risk is determined by the chemical form and type of exposure.
According to the American Academy of Pediatrics, “Mercury in all of its forms is toxic to the fetus and children, and efforts should be made to reduce exposure to the extent possible to pregnant women and children as well as the general population.”
U.S. Environmental Protection Agency
While naturally occurring in the environment, mercury is also released through industrial pollution, such as from coal-fired power plants. It falls from the air in rain and other forms of precipitation, getting into surface water and working its way into streams, lakes, and the ocean. Bacteria then cause chemical changes that transform mercury into a highly toxic form, methylmercury. Fish consume methyl mercury as they feed on aquatic organisms and other fish. The toxin then accumulates in the tissues of fish and travels up the food web over time through the process of bioaccumulation. Smaller, younger fish tend to have lower concentrations of methylmercury, though their level of contamination is highly contingent upon geological, geographical and ecological conditions*.
Although dangerous, mercury can be eliminated from our bodies over time. For a person who has had long-term consistent exposure, it can take up to a year to fully eliminate methyl mercury from the body.
Researchers have tracked historic and recent mercury accumulation trends both in the environment and in animals. Several studies have found that tissue sample methylmercury concentrations from birds and fish have increased over time. These findings suggest that elevated methylmercury levels are largely consistent with an increase in global mercury emissions. As such, the risk of toxic exposure through consumption may continue to increase for humans and other animals alike. Significantly more research is needed to understand how ecological and biological characteristics influence mercury accumulation in the natural environment, in fish species, and in humans.
*http://www.momscleanairforce.org/resources/how-mercury-poisoning-works/
PCBs
PCBs are man-made organic chemicals that belong to a family of chlorinated hydrocarbons. PCBs have been demonstrated to cause a variety of health problems, including impairment of the immune, reproductive, nervous and endocrine systems. Studies suggest PCBs are probable carcinogens and can lead to cancer and associated diseases in humans.
PCBs were produced in the United States for industrial and commercial applications from 1929 until 1979, when their manufacture and use was banned. Before the ban, PCBs typically entered the environment through the manufacturing process. Today, PCBs are commonly released into the environment by the improper disposal or burning of PCB-laden material and leakage or release from electrical transformers.
PCBs are known as legacy chemicals because they do not easily break down once they enter the environment. Therefore, even though companies are no longer producing PCBs, they continue to cycle through the environment for years and accumulate in the tissue of fish. Seafood contamination is a major source of PCB exposure, yet incidences of this are rare.
* U.S. Geological Survey. 2002. “Mercury in the Environment”
