Poly-chlorinated biphenyls (PCBs)

Poly-chlorinated biphenyls (PCBs)

Polychlorinated biphenyls (PCBs) are a class of highly stable, non-corrosive and relatively non-flammable chemicals, which were first manufactured on a commercial scale in 1929.  For several decades they were used extensively in a wide range of industrial applications, including cutting oils, sealants, caulking compounds, inks, carbonless copy paper, paint additives, and, in particular, as coolants and lubricants in closed electrical applications, such as transformers and capacitors.

            In the 1970s, concern over the impact of PCBs on the environment, and their persistence, led to their replacement, and eventually resulted in a North America ban in 1977, on the manufacture, importation, and most non-electrical applications of PCBs. Electrical applications of PCBs are now being phased out, and stringent for handling, storage and disposal have been specified.

 Where they are found?

 Studies have identified trace levels of PCBs everywhere in the environment, throughout the world.  This is thought to be due to improper disposal practices, accidental releases from the 1930s to the 1970s, and subsequent long-range transport by global air currents. Once in the environment, PCBs are extremely persistent (they do not break down easily in the environment, and tend to last for many years). PCBs also have tendency to bioconcentrate (bio-accumulate/bio-magnify) as they move up the food chain; they generally accumulate in fatty tissues of animals and humans, where they can remain.

Although PCBs are no longer being manufactured, significant amounts remain in certain types of electrical equipment. As well, public concern over how to dispose of PCBs properly has led to stockpiling of these substances at sites across Canada. Despite stringent safeguards over storage of PCBs and PCB-contaminated wastes, accidental releases into the environment remain a potential risk.

 Exposure

Everyone is exposed to very small amounts of PCBs, principally through food, and to a lesser extent, air and water. As a result, everyone will have a detectable level of PCBs in their body fat and blood. These levels are unlikely to cause any adverse health affects.

            Based on results from Canadian Market Basket Surveys and other information, the estimated daily intake of PCBs from all sources, for the average Canadian, is less than one microgram per day. However, consumption of certain contaminated foods, such as sports fish, wildlife or marine mammals can increase this exposure.

            Unintentional releases, such as uncontrolled fires involving PCBs, are another way that PCBs can be released to the environment to pose an additional risk of exposure. When PCBs are burned, they may be transformed into an array of dangerous chemicals, including polychlorinated dibenzofurans, and occasionally polychlorinated dibenzodioxins (see the “It’s Your Health” fact sheet series on Dioxins and Furans). Following a fire, airborne particulates containing these toxic chemicals may settle on a variety of surfaces, including soil and water, thereby resulting in as potential for human exposure.

            Due to restrictions on the use of PCBs, anticipated occupational exposures will be minimal. The only workplace exposures in the future will probably be from replacing or servicing old electrical equipment, transporting PCBs to hazardous waste storage and destruction facilities. Workers involved in these activities should wear protective clothing and follow decontamination procedures on completion of the work.

 Health Effects

         Much of our understanding of the health effects of PCBs is related to higher level exposures.  Such as occupational or accidental exposures. Adverse health effects includes a severe form of acne (chloracne), swelling of the upper eyelids, hyperpigmentation of the nails and skin, numbness of limbs, weakness, muscle spasms, chronic bronchitis, and a variety of subjective neurological complaints.  It is important to note that these effects occur at exposure that are much higher than levels normally encountered in the environment.

            Scientists generally agree that short-term, low level exposure to PCBs is unlikely to have a significant health impact.  Subpopulation that have been identified as being at increased risk of exposure and health affects include Aboriginal people, anglers and hunters and their families, and subsistence groups that consume large amounts of fish and game.  There is, however, some speculation over the possibility of adverse effects associated between such exposure and subtle physical and neurodevelopmental effects in newborns and children.  More extensive studies are required to further elucidate the nature and extent of such a link, and determine the role, if any, played by the simultaneous exposure to other contaminants.

         The International Agency for Research on Cancer has concluded that there is some evidence to link long term, highly-level, PCB exposure in occupational settings to an increased incidence of cancer, particularly liver and kidney cancer. This conclusion is based on studies of humans exposed to PCBs contaminated with polychlorinated dibenzofurans, which may play a role in cancer development.

 What is being done about PCBs

Both Health Canada and environment Canada have taken vigorous steps, through specific regulations under the Canadian Environmental Protection Act to control PCB use, importation, manufacture, storage, destruction and release.

The long-term solution to the problem is to destroy the remaining stores of PCBs, thereby preventing their entry into the environment.  The most widely used and proven technology for destroying PCBs is highly-temperature incineration.  Properly done, this method has been shown to destroy PCBs at an efficiency of greater than 99.9 per cent without producing toxic by products.  The government of Canada has chosen to eliminate liquid PCBs primarily by this method.

Health Canada has established PCB exposure limits for various foods consumed by Canadians.  Federal regulatory agencies, including Health Canada, also monitor typical Canadian diets, specific foods, air and water to ensure that the public is not exposed to PCB levels that pose a health risk.  At the same time, research is continuing to assess the health implications of sustained low-level exposure to PCBs.

 Conclusion

             While exposures to PCBs in the general population are quite low and most PCB mixtures have a very low toxicity in humans, exposure should be kept to a minimum.  Research, regulation and monitoring of human exposures to PCBs remain a high priority of the Government of Canada, in order to ensure that the health of Canadians is not at risk. Nonetheless, in Malaysia these substances are regulated as Scheduled Wastes that sees the industrial and many services sectors in active compliance efforts. Ironically, PCBs are well dispersed within the general public in a wholesome of consumer appliances and goods that escaped the sight of this law.