Polychlorinated biphenyls (PCBs)


Polychlorinated biphenyls (PCBs) are a group of manufactured organic chemicals that contain 209 individual chlorinated chemicals (known as congeners). Concentrated PCBs are either oily liquids or solids and are colorless to light yellow in color. They have no known smell or taste. There are no known natural sources of PCBs. Some commercial PCB mixtures are known in the United States by their industrial trade name, Aroclor.

PCBs don't burn easily and are good insulating material. They have been used widely as coolants and lubricants in transformers, capacitors, and other electrical equipment. The manufacture of PCBs stopped in the United States in 1977 because of evidence that they build up in the environment and cause harmful health effects. Products containing PCBs are old fluorescent lighting fixtures, electrical appliances containing PCB capacitors, old microscope oil, and hydraulic fluids.

During the time that PCBs were manufactured, there were often no effective controls on disposal. Because they do not break down easily, PCBs are now found widely distributed in our environment. Generally their concentrations in the environment are quite low. However, the chemical properties of PCBs cause them to be concentrated up the food chain.

Human Health Effects
PCBs are a probable human carcinogen.
The International Agency for Research on Cancer and the Environmental Protection Agency classify PCBs as a probable human carcinogen. The National Toxicology Program has concluded that PCBs are reasonably likely to cause cancer in humans. The National Institute for Occupational Safety and Health has determined that PCBs are a potential occupational carcinogen.

Studies of PCBs in humans have found increased rates of melanomas, liver cancer, gall bladder cancer, biliary tract cancer, gastrointestinal tract cancer, and brain cancer, and may be linked to breast cancer. PCBs are known to cause a variety of types of cancer in rats, mice, and other study animals.

Why are PCBs called a `probable´ carcinogen?
EPA´s regulations on cancer-causing chemicals use the term `probable´ when a chemical is known to cause cancer in animals and where there is evidence that suggests that it causes cancer in humans but which is not conclusive. Because you can´t feed chemicals to humans to see how they respond, it is much more difficult to demonstrate carcinogenicity in humans than in animals. Instead, studies are undertaken of groups who have been exposed to a chemical, and if they suffer from more cancers than would be expected at normal levels, this may indicate that the chemical was a carcinogen. However, there are many difficulties doing these studies: small numbers of people known to be exposed to a chemical; the fact that people suffer from many cancers without any chemical exposure; the fact that in some cases these people were exposed to a number of other chemicals; and the need to demonstrate high cancer rates that cannot be random in order to draw conclusions. Thus the term `probable´ reflects the limited nature of the studies, and it is rare that a carcinogen is so effective that it can be called a `known´ human carcinogen. The fact that PCBs are called a `probable´ carcinogen should not be taken as a sign that they are benign.

Acute toxic effects
People exposed directly to high levels of PCBs, either via the skin, by consumption, or in the air, have experienced irritation of the nose and lungs, skin irritations such as severe acne (chloracne) and rashes, and eye problems.

PCBs cause developmental effects
Women exposed to PCBs before or during pregnancy can give birth to children with significant neurological and motor control problems, including lowered IQ and poor short-term memory. A group of children in Michigan whose mothers had been exposed to PCBs were found to have decreased birth weight and head size, lowered performance on standardized memory, psychomotor and behavioral tests, and lowered IQ. These effects lasted through at least 7 years. A group of women occupationally exposed to PCBs in upstate New York had shorter pregnancies and gave birth to children with lower birth weight. Another study, of the chidren of women who ate contaminated Lake Ontario fish, found significant performance impairments on a standardized behavioral assessment test. Exposure of one form of PCB to rats resulted in retarded growth, delayed puberty, decreased sperm counts, and genital malformations. In other studies, exposure of PCBs to rats in utero led to behavioral and psychomotor effects that lasted into adulthood.

PCBs disrupt hormone function
PCBs with only a few chlorine atoms can mimic the body´s natural hormones, especially estrogen. Women who consumed PCB-contaminated fish from Lake Ontario were found to have shortened menstrual cycles. PCBs are also thought to play a role in reduced sperm counts, altered sex organs, premature puberty, and changed sex ratios of children. More highly-chlorinated PCBs (with more chlorine atoms) act like dioxins in altering the metabolism of sex steroids in the body, changing the normal levels of estrogens and testosterone. PCBs tend to change in the body and in the environment from more highly-chlorinated to lower-chlorinated forms, increasing their estrogenic effects.

Immune system and thyroid effects
In a study of adolescents Mohawk males in New York State, PCBs were shown to upset the balance of thyroid hormones, which may affect growth as well as intellectual and behavioral development. Like dioxin, PCBs bind to receptors that control immune system function, disturbing the amounts of some immune system elements like lymphocytes and T cells.
In a study of Dutch children, PCB levels were tied to an increased prevalence of ear infections and chickenpox and with lowered immune system function, and thus greater susceptibility to disease.

Eating fish is the major route of exposure to PCBs
The most common route of exposure to PCBs is from eating contaminated fish. The EPA estimates an increased cancer risk as high as 1 in 2500 for people eating certain species of fish from the Hudson River&em; thousand times higher than the EPA´s goal for protection.
Air near a contaminated site may also be polluted by PCBs. By one estimate, residents of the Hudson Valley may inhale as many PCBs as they would get by eating one contaminated fish per year. Although small amounts of PCBs can enter the body from swimming in highly contaminated water, this is unlikely to be significant except in the most extreme cases.
Municipalities that use the Hudson River as a drinking water source carefully monitor the water for PCBs, and there are no detectable levels in the water supplies.

PCBs accumulate in the body and in the ecosystem
Once PCBs enter a person´s (or animal´s) body, they tend to be absorbed into fat tissue and remain there.
Unlike water-soluble chemicals, they are not excreted, so the body accumulates PCBs over years. This means that PCBs also accumulate via the food chain: a small fish may absorb PCBs in water or by eating plankton, and these PCBs are stored in its body fat. When a larger fish eats the small fish, it also eats and absorbs all the PCBs that have built up in the small fish. In this way, larger fish and animals can build up a highly concentrated store of PCBs. Some types of PCBs may degrade into nontoxic form while they are stored in the body, but this process can take many years.
In the same way, PCBs accumulate in women and pass on to their infants through breast milk. This accumulation means that nursing infants may ingest PCB levels much higher than the levels in fish and other foods consumed by their mothers.
PCBs have been found all over the world, including significant amounts in the Arctic and Antarctic, far from any sources. In fact, several studies have found very high levels of PCBs in the blood and breast milk of Inuit women. It is thought that PCBs spread through the air, after evaporating from contaminated water and sediments, as well as through the water.

References
https://www.dhs.wisconsin.gov/environmental/pcb-fish.htm
http://www.clearwater.org/news/pcbhealth.html

Recent Publications
Exposure to 27 polychlorinated biphenyls in the indoor environment of a workplace: a controlled bio-monitoring study
Health risk assessment of migrant workers' exposure to polychlorinated biphenyls in air and dust in an e-waste recycling area in China: Indication for a new wealth gap in environmental rights
Polychlorinated biphenyl (PCBs) in rice grains and straw; risk surveillance, congener specific analysis, distribution and source apportionment from selected districts of Punjab Province, Pakistan
Toxicokinetics of chiral polychlorinated biphenyls across different species—a review
Evaluation of trace metal and polychlorinated biphenyl levels in tea brands of different origin commercialized in Italy
Characterization of the biosorption and biodegradation properties of Ensifer adhaerens: A potential agent to remove polychlorinated biphenyls from contaminated water