Wednesday, 11 April 2018

What is polychlorinated Biphenyls (PCBs)?

PCBs are a group of man-made organic chemicals consisting of carbon, hydrogen and chlorine atoms. The number of chlorine atoms and their location in a PCB molecule determine many of its physical and chemical properties. PCBs have no known taste or smell, and range in consistency from an oil to waxy solid. They belong to a broad family of man-made organic chemicals known as chlorinated hydrocarbons.  They are a group of 209 different chemicals that share a common structure but vary in the number of attached chlorine atoms.
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 likely to cause cancer in humans. The National Institute for Occupational Safety
and Health has determined that PCBs are a potential occupational carcinogen. PCBs are known to cause a variety of types of cancer in rats, mice, and other study animals and 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 as well.
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), rashes, and eye problems. Products that may contain PCBs. Include; transformers, capacitors, electrical equipment such as voltage regulators and switches, hydraulic system, plastics and cable insulation to mention but few. 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, decreased birth weight and head size. 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 the uterus led to behavioral and psychomotor effects that lasted into adulthood. PCBs with only a few chlorine atoms can mimic the body´s natural hormones, especially estrogen. Women who consumed PCB-contaminated fish 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.
In a study of adolescent males, PCBs were shown to upset the balance of thyroid hormones, which may affect growth as well as intellectual and behavioural development.  Like dioxin, PCBs bind to receptors that control immune system function, disturbing the amounts of immune
system elements like lymphocytes and T cells.  In another study, PCB levels were tied to an increased prevalence of ear infections, chickenpox and lowered immune system function which automatically leads to greater susceptibility to disease.
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. Air near a contaminated site may also be polluted by PCBs. 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. 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. It is thought that PCBs spread through the air, after evaporating from contaminated water and sediments, as well as through the water.
Source:, Wikipedia and

By Mercy Kukah

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