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What are PCBs? Are PCBs still entering the environment? How long will PCBs remain a problem? How do PCBs enter the human body? Are humans affected by PCBs? How is the public protected? What are PCBs? Polychlorinated biphenyls (PCBs) are colorless and odorless chemicals that were widely used in electrical equipment such as transformers and capacitors before their production was banned in 1976. During their manufacture, there are over 200 individual PCB compounds that can be produced when chlorine is added to a biphenyl ring structure. The same properties that made PCBs so useful in industrial applications such as their stability and non-flammability, enable PCBs to persist in the environment for long periods of time. Are PCBs still entering the environment? Yes. Of the 1.2 billion pounds of PCBs produced in the U.S. before 1976, about half has entered the environment through discharges to the air, land, and water. In addition, products that contain PCBs are still often being disposed of improperly. Most PCBs that have entered the environment end up in rivers, lakes, and ultimately the ocean. PCBs enter the food chain and become progressively concentrated from small organisms to larger fish and mammals. Many large, fatty fish like lake trout, carp, and chinook salmon have been found to contain very high concentrations of PCBs. As a result, some fish may contain high enough levels that they are considered unsafe for human consumption, or with concentration levels where consumption should be restricted. How long will PCBs remain a problem? Most PCBs tend to build up primarily in fatty tissue in fish and to a less extent in edible muscle tissue. Larger, fattier fish tend to accumulate PCBs to a greater extent than younger, leaner fish. With an environmental half-life as high as five years, PCBs may remain a problem for quite some time. Because PCBs become attached to particles in the water, they eventually settle out and are buried in bottom sediments. As bottom-dwelling organisms feed, they ingest these PCB-contaminated sediments and pass them up into the food chain. The smallest aquatic organisms are eaten by successively larger, predator fish which are then consumed by fish-eating mammals. PCBs have been detected in both fresh and saltwater fish in varying amounts depending on size, feeding grounds, position in the food chain, exposure and fat content. How do PCBs enter the human body? PCBs can be absorbed through the skin, lungs or GI tract. For most of us, food is by far the most significant source of exposure. Foods most likely to contain PCBs include milk, eggs, chicken, turkey, beef, and fish. PCBs are stored in the body's fatty tissue where they can accumulate. Since 1977 when manufacturing of PCBs was banned, levels in most foods have declined. Are humans affected by PCBs? Yes, medical studies indicate health risks are highest in the fetus or nursing infant, especially if the mother is or has been exposed to PCBs. Women of childbearing age, especially those pregnant or nursing, are advised to minimize risk of exposure by avoiding eating fish from waters known to contain PCB contaminants. Most knowledge about the adverse human health effects of acute (high level, short duration) exposure to PCBs has come from occupational studies. Workers exposed in the late 1960s to high levels of PCBs after industrial accidents experienced eye irritation, headache, fatigue, skin eruptions, nausea, vomiting, digestive disturbances and liver dysfunction. With respect to the effects of chronic or low-level exposure to PCBs over time, less is known about potential adverse health effects. However, medical authorities suspect prolonged exposure to small doses of PCBs can contribute to a variety of human health problems, including developmental problems in children, liver damage and various forms of cancer. How is the public protected from consuming contaminated fish? Two federal agencies have responsibility in protecting humans from exposure to harmful levels of PCBs. The U.S. Food and Drug Administration (FDA) is responsible for setting the standards for tolerable levels of PCBs in fish sold via interstate commerce. In 1984, the FDA lowered the allowable level of PCBs from 5.0 ppm (5 parts PCB per million parts edible fish) for fish and shellfish to 2.0 ppm. The FDA periodically tests fish typically sold in markets to determine the levels of PCBs and other contaminants and when necessary, confiscates contaminated products. Another agency that regulates PCBs is the U.S. Environmental Protection Agency (EPA). The EPA sets standards based exclusively on protection of public health, whereas the FDA has to consider many factors including economics. Currently, the EPA's Office of Water health screening level for all PCBs in fish tissue is 0.01 ppm. At this level in fish tissue, we would expect one additional cancer due to PCBs in a population of 100,000, assuming an adult (70 kg) eats 1 meal/month (6.5 g/day) over a lifetime. |
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