PCBs (Polychlorinated Biphenyls) are notoriously hazardous chemicals produced commercially since 1929. They have now infiltrated our food chain. PCBs are a member of the POPs (persistent organic pollutants) family. They are commonly known as synthetic chlorinated hydrocarbon compounds and chances are they may just be on your dinner plate.
An important property of PCBs is their general inertness. Resistant to acids and bases, and able to maintain thermal stability, they are useful in electrical insulation. When combusted, PCBs release harmful byproducts. PCB ingestion can lead to cancer, hormonal problems, and reproductive complications. Due to the value of this compound to industry, production continued even though negative health effects started to arise. PCB production and subsequent environmental contamination went unchecked from 1929-1979 wherein the EPA stepped in and halted any further production in the United States. Because of these and other harmful impacts to health and the environment, PCBs are now either severely restricted or banned completely in over 120 countries.
PCBs do not dissolve in water and are stable in both hot and cold temperatures. They enter the environment mainly through waterways. This entry can be from direct pollution such as a company dumping waste into a river or indirect through air pollution. From the air, they can settle onto grasslands, farms, and backyards. Eventually the PCBs then find their way into waterways and to the oceans where the compounds are transported around the planet by ocean currents and in the tissues of migrating fish. The Inuit Eskimos have been known to carry some of the highest PCB concentrations in their bodies due to their high fish diet. Although not water soluble, PCBs do dissolve in oil and fats making marine mammals a high-risk group. Since they cannot detoxify the chemical from their bodies, mammals store it in their fat and blubber.
A virtual PCB reservoir may exist in ocean, lake, and river bottoms while slowly being released back into the water column. Once in the water, PCBs concentrate in phytoplankton algal cells, which use sunlight for energy and growth. These cells either die or are consumed by zooplankton. Either way, dead plankton cells sink to the bottom and build up in the sediment or are eaten by small fish and/or invertebrates. Highly chlorinated PCBs, called congeners, adhere strongly to soil and can persist for decades. Soil turbulence brought upon by passing boats and burrowing organisms can release the PCBs back into the water starting the whole process over again. The cells that are eaten by small fish and invertebrates transfer their stocks of PCB to their predators. As it bioaccumulates, PCB levels continue to rise until salmon, bald eagles, and other members at the top of the food chain become affected.
Consumption of animal fat and harvested fish from contaminated sites are the main source of human PCB contamination. Researchers have also found that shellfish accumulate PCBs as they filter feed plankton. Cows grazing on contaminated grasses and feed can transfer them into their fat, meat, and milk. A study of the vegetation-deer food chain in Quebec showed that deer PCB levels rose a substantial amount from 1999-2002. These dates coincide with the opening of magnesium smelter plant in 1999, which produces PCBs as a byproduct in production.
PCBs absorb readily from the gastrointestinal tract and then can deposit in liver and fat tissue. They have an ability to cross the placenta and are excreted in breast milk. Needless to say, a developing fetus ingesting contaminated milk may experience problems. Studies have shown PCBs effect sperm motility, fetal growth, and neurological development in offspring (lower IQ scores, slower reflexes, attention deficit disorder, reduced memory capacity). Cases of liver cancer and malignant melanoma were noted, but researchers say the relationship to PCBs is not clear.
Contamination of the Great Lakes is especially problematic due to the fact that it contains 20% of the world's fresh water. Less than 1% of that water flows outward making them a nearly closed system. Population declines in lake trout and salmon as well as birds that prey upon them have sparked grass-root efforts from environmental groups to cleanup the contamination. Estimated costs to solve this problem are immense. The EPA approximates that one relatively small area of contamination could cost millions of dollars and take years to complete. Despite that fact, the EPA and environmental groups still maintain that the benefits of remediation of the Great Lakes are at least as great as the costs.
General Electric used PCBs to make electrical equipment. Located on the shores of the Hudson River, GE waste flowed directly into it. The EPA, in 2000, after 16 years of studies, announced a 5-year plan to clean up 2.65 cubic million yards pf PCB-contaminated sediment in the river. GE had issues with the proposed plan. Rather than the actual dollar figure that GE would have to pay to dredge the river, officials at the company chose to focus on alternative cleanup measures. They felt that an installed groundwater pump and treat system should reduce the flow of PCBs into the river. After that, the rivers natural recovery system should take care of the rest. GE also stated that PCB levels have come down 90% since 1977 and burial of the older PCB contaminated sediments by newer, cleaner sediments would take the chemical out of the food chain. Environmental groups disagreed citing that officials had found high PCB levels in floodplain shores and that the toxin had entered the land food chain in populations of turtles, otter and mink. EPA scientists refuted the claims made by GE and stood firm by their decision announcing in that GE would have to move forward and fund the dredging cleanup. Many other EPA superfund sites have GE listed as the responsible party for PCB contamination.
Degradation in soil depends on location of chlorination in the molecule, concentration of PCBs in the soil, type of bacterial population present, available nutrients, and temperature. The most common aerobic (with oxygen) degradation process is when a bacterial colony break PCBs down to a chloride acid (benzoic acid), carbon dioxide, and inorganic chlorides. These components are now more environmentally benign and able to be broken down further and reintroduced to the ecosystem. Natural enzymes in certain bacterial populations allow them to start the degradation process.
Bioremediation is a process of purposefully unleashing living organisms on chemicals with the hopes of reducing its levels in the environment. It takes a multitude of chemical steps in order to breakdown PCBs. If bacteria can't complete each step, then the process becomes useless. Researchers are working on isolating a step that some species of bacteria can't resolve. Since bacteria can produce new generations in minutes, researchers can efficiently determine if the process will be promising or if more work needs to be done. Turning hazardous chemicals into benign environmental molecules could eliminate the cost of transporting PCB laden soil to an incinerator. It seems that this may be the most cost efficient and environmentally friendly way to reduce a dangerous toxin from our environment, food, and bodies.
PCBs in our environment are not a new phenomenon, but rather and old injury the environment must deal with. It is pressure on private industry and governmental organizations to deal with the problem effectively that seems to work best. Companies that produced these toxins years ago are reluctant to pay for their cleanup now. One thing is clear, PCBs will not go away by themselves and maybe, as science moves forward, one day PCBs won't be on your dinner plate.
If you need to cite this page, you can copy this text:
Tim Fitzpatrick. PCBs (Polychlorinated Biphenyls) are in the Foods You Love. EnvironmentalChemistry.com. Jan. 31, 2006. Accessed on-line: 11/27/2014