Polychlorinated biphenyls (PCBs)
Polychorinated biphenyls (PCBs)
Polychlorinated biphenyls (PCBs) belong to a broad family of man-made organic chemicals known as chlorinated hydrocarbons. PCBs were domestically manufactured from 1929 until their manufacture was banned in 1979. Although PCBs are no longer made in the United States, people can still be exposed to them. They have a range of toxicity and vary in consistency from thin, light-colored liquids to yellow or black waxy solids. PCBs have been demonstrated to cause a variety of adverse health effects. They have been shown to cause cancer and non-cancer health effects in animals, including effects on the immune system, reproductive system, nervous system, endocrine system and also other health effects. Studies in humans provide supportive evidence for potential carcinogenic and non-carcinogenic effects of PCBs. In the environment PCBs do not readily break down and therefore may remain for long periods of time cycling between air, water, and soil (EPA).
Although no longer commercially produced in the United States, PCBs may be present in products and materials produced before the 1979 PCB ban. Products that may contain PCBs include:
• Transformers and capacitors
• Other electrical equipment including voltage regulators, switches, reclosers, bushings, and electromagnets
• Oil used in motors and hydraulic systems
• Old electrical devices or appliances containing PCB capacitors
• Fluorescent light ballasts
• Cable insulation
• Thermal insulation material including fiberglass, felt, foam, and cork
• Adhesives and tapes
• Oil-based paint
• Carbonless copy paper
• Floor finish (EPA).
Routes of Exposure and Metabolism
PCBs can enter human cells and tissues when contaminated air is breathed in, when contaminated food enters the digestive system, or through contact with the skin. Tests on laboratory animals show that PCBs are readily absorbed through the digestive tract when swallowed, and to a lesser extent through the skin. The main PCB elimination routes are through the faeces, urine, and breast milk (GreenFacts, ATSDR-Public Health Statement).
Once in the gastrointestinal tract, ingested PCBs diffuse across cell membranes and enter blood vessels and the lymphatic system. PCBs, especially those that contain a greater number of chlorine atoms, are readily soluble in fats and thus tend to accumulate in fat-rich tissues such as the liver, brain and skin. PCBs can undergo different transformations in the body and then either be stored in certain tissues or excreted (GreenFacts). In mothers, PCBs have also been found to pass into the placenta, umbilical cord blood, and breast milk (GreenFacts).
A common way for PCBs to enter the human body is by eating meat or fish products or other foods that contain PCBs. Exposure from drinking water is less than from food. It is also possible that PCBs can enter your body by breathing indoor air or by skin contact in buildings that have the kinds of old electrical devices that contain and can leak PCBs. For people living near waste sites or processing or storage facilities, and for people who work with or around PCBs, the most likely ways that PCBs will enter their bodies are from skin contact with contaminated soil and from breathing PCB vapors (ATSDR-Public Health Statement).
Human Health Effects
The Japanese scientist Hideshige Takada leads a study into global patterns of oceanic chemical pollution. But he uses a highly remarkable way of samping the water. Takada uses the industrial plastic granules (pellets) that litter our oceans worldwide. These granules act as a sponge that bind all sorts of chemical pollutants like PCB’s, remains of DDT etc., from the seawater to their surface. By collecting such plastic pellets from beaches all over the world, patterns of pollution may be detected. January 2010
Acute Health Effects
According to PANNA (Pesticide Action Network North America), Aroclor is listed by the EPA as beingslightly toxic (it has effects on eye-irritation and corneal inovolvement, clearing takes 7 days or less; and effects on skin-moderate irritation at 72 hours of exposing). Acute animal tests in rats have shown PCBs to have moderate acute toxicity from oral exposure (EPA-Aroclors).
Chronic Health Effects
According to PANNA, Aroclor is listed as “probable carcinogen” by IARC (International Agency for Research on Cancer) and by U.S. EPA. It is listed as an endocrine disruptor by EU list (European Union Prioritization List). PANNA also reports that Aroclor has reproductive/developmental effects: it is listed on the State of California’s Proposition 65 List (a list of chemicals “known to the State to cause reproductive and developmental toxicity” is maintained by the State of California under the Safe Drinking Water and Toxic Enforcement Act of 1986 (Proposition 65)).
- Immune Effects
A recent study in humans found that individuals infected with Epstein-Barr virus had a greater association of increased exposures to PCBs with increasing risk of non-Hodgkins lymphoma than those who had no Epstein-Barr infection. This finding is consistent with increases in infection with Epstein Barr virus in animals exposed to PCBs. Since PCBs suppress the immune system and immune system suppression has been demonstrated as a risk factor for non-Hodgkin’s lymphoma, suppression of the immune system is a possible mechanism for PCB-induced cancer. Immune effects were also noted in humans who experienced exposure to rice oil contaminated with PCBs, dibenzofurans and dioxins (EPA-Health Effects of PCBs).
- Neurological Effects
Proper development of the nervous system is critical for early learning and can have potentially significant implications for the health of individuals throughout their lifetimes. Effects of PCBs on nervous system development have been studied in monkeys and a variety of other animal species. Newborn monkeys exposed to PCBs showed persistent and significant deficits in neurological development, including visual recognition, short-term memory and learning. Some of these studies were conducted using the types of PCBs most commonly found in human breast milk.
Studies in humans have suggested effects similar to those observed in monkeys exposed to PCBs, including learning deficits and changes in activity associated with exposures to PCBs. The similarity in effects observed in humans and animals provide additional support for the potential neurobehavioral effects of PCBs (EPA-Health Effects of PCBs).
- Other Non-cancer Effects
A variety of other non-cancer effects of PCBs have been reported in animals and humans, including dermal and ocular effects in monkeys and humans, and liver toxicity in rodents. Elevations in blood pressure, serum triglyceride, and serum cholesterol have also been reported with increasing serum levels of PCBs in humans (EPA-Health Effects of PCBs).
Environmental Health Effects
Once released into the environment, the compositions of commercial PCB mixtures are altered through processes such as volatilization and other kinds of partitioning, chemical or biological transformation, and preferential bioaccumulation. These processes are dependent upon the degree of chlorination of the biphenyl molecule. Bioaccumulated PCBs are of particular relevance to human health because of their persistence in the body (ATSDR-Toxicological Profile for PCBs).
In the environment PCBs do not readily break down and therefore may remain for long periods of time. They can cycle between air, water, and soil. PCBs can be carried long distances and have been found in snow and sea water in areas far away from where they were released into the environment. As a consequence, PCBs are found all over the world. In general, the lighter the form of PCB, the further it can be transported from the source of contamination (EPA).
PCBs, particularly the higher chlorinated congeners, adsorb strongly to sediment and soil, where they tend to persist with half-lives of months to years. PCBs bioaccumulate in food chains and are stored in fatty tissues due to their stability and lipophilicity (ATSDR-Toxicological Profile for PCBs).
PCBs can accumulate in the leaves and above-ground parts of plants and food crops. They are also taken up into the bodies of small organisms and fish. As a result, people who ingest fish may be exposed to PCBs that have bioaccumulated in the fish they are ingesting (EPA).
Toxic concentrations of PCBs can be also found in piscivorous birds (e.g., gulls, terns, and cormorants) and mammals (e.g., minks, otters, seals, and sea lions) (ATSDR-Toxicological Profile for PCBs).
Ways to Reduce Exposure
The Toxic-free Legacy Coalition of Washington State offers these guidelines for reducing exposure to PCBs in food:
• Choose fish wisely
Check with state advisories before eating sport-caught fish or shellfish, which are often high in PCBs and DDT. Commercial fish that are high in PCBs include Atlantic or farmed salmon, bluefish, wild striped bass, white and Atlantic croaker, lackback or winter flounder, summer flounder, and blue crab. Commercial fish that contain higher levels of pesticides, including DDT, are bluefish, wild striped bass, American eel, and Atlantic salmon.
When preparing fish, remove the skin, trim the fat, and broil, bake, or grill the fish so that the fat drips away; this will reduce your exposure to PCBs and other toxic chemicals that have accumulated in fatty tissue.
• Make your meat lean
When it comes to meat, choose lean meat cuts, and buy organic meats if possible. Cut off visible fat before cooking meat and choose lower-fat cooking methods: broiling, grilling, roasting or pressure-cooking.
• Limit dairy fat (Pollution in People).
Children should be told that they should not play with old appliances, electrical equipment, or transformers, since they may contain PCBs. Children who live near hazardous waste sites should be discouraged from playing in the dirt near these sites and should not play in areas where there was a transformer fire. In addition, children should be discouraged from eating dirt, and careful handwashing practices should be followed (ATSDR-Public Health Statement).