The New Straits Times, February 12, 1998
Q: You have highlighted that polychlorinated biphenyls (PCBs) would normally be released from dumpsite fires. Can you describe the effect of PCBs on health and the environment?
Polychlorinated biphenyls are synthetic chemical compounds consisting of chlorine, carbon and hydrogen. PCBs are also known by their various brand names which include Aroclor, Pyranol, Interteen and Hyvol. PCBs are relatively fire-resistant, very stable, do not conduct electricity and have low volatility at normal temperatures.
These and other properties have made them desirable components in a wide range of industrial and consumer products. These same properties make the PCBs environmentally hazardous - especially their extreme resistance to chemical and biological breakdown by natural process in the environment. Because of their stability, PCBs have a high potential for bioaccumulation, which is an important factor to consider due to their ability to accumulate in aquatic environments such as lakes and rivers.
In terms of their physical properties, PCB mixtures are usually light-coloured liquids that feel like thick, oily molasses. However, some PCB compounds form sticky, yellow liquids or a brittle gum ranging in colour from amber to black. PCBs are soluble in most organic solvents but are almost insoluble in water, so when added to it they sink to the bottom.
Most PCBs are non-volatile at room temperatures (for instance, below 40 C). However, overheating of electrical equipment containing PCBs can produce emissions of irritating vapours.
In the earlier usage of PCBs especially during the first 25 years, few concerns were raised about any negative impacts of these compounds. In the late 1960s, however, the discovery of PCBs in birds and the poisoning of 1,200 people by rice oil containing PCBs focused public attention on the problem.
By 1972, scientific evidence suggested that PCBs posed a serious potential hazard to the environment and human health.
Because their hazardous nature has only recently been understood, PCBs have been routinely disposed of over the years without any precautions being taken. As a result, large volumes of PCBs have been introduced into the environment through open burning or incomplete incineration; by vapourisation from paints, coatings and plastics; by direct entry or leakage into sewers and streams; by dumping in non-secure landfill sites and municipal disposal facilities; and by other disposal techniques (e.g. ocean dumping) which did not destroy material.
The environmental concern of PCBs arose because of their tendency to accumulate in living organisms. Thus, when these compounds are taken up by living organisms, they would be stored and concentrated along the food chain cycle. This bioaccumulation raised concern because of the wide dispersal of PCBs in the global environment and the potential adverse effects they can have on various organisms, including humans.
While there have been many laboratory experiments and other studies which have tried to determine the full health effects of PCBs on humans, none has been definitive. As a result, even expert opinion varies significantly on this subject. Scientists generally agree it is unlikely that serious injury would result from short-term low-level exposure to PCBs.
However, most are concerned about possible adverse long-term exposure to even low concentrations of these substance. PCBs can enter the body through skin contact, by the inhalation of vapours or by ingestion of food containing PCB residues.
The most commonly observed health effect from extensive exposure to PCBs is chloracne, a painful and disfiguring skin condition, similar to adolescent acne. Liver damage can also result.
People who might be exposed to PCBs include those servicing some types of electrical equipment, maintenance workers who clean up spills or leaks of PCB fluids, employees of scrap metal or salvage companies, and waste collection workers.
Chronic exposure of animals to PCBs can lead to disrupted hormone balances, reproductive failures as well as carcinomas. A more significant health impact of PCBs may be caused by their incomplete combustion during thermal treatment processes. Incomplete oxidation of PCBs may form polychlorinated dibenzofuran (PCDF) emission.
These are of concern due to their toxicological and lethal effects on laboratory animals.
Besides the animal studies and the acute health effects, another study published in the New England Journal of Medicine (Sept 1996) also showed that children exposed to low levels of PCBs in the womb would grow up with low IQs, poor reading comprehension, difficulty paying attention and memory problems.
Based on this study, 242 children were monitored for their mental and physical growth since birth after being confirmed to be exposed to PCBs.
Among the findings from this study were as follows: At the age of four, two effects became apparent among these selected children.
Firstly, 17 of the children whose mothers had the highest levels of PCBs in their breast milk refused to complete the tests; they were balky and unco-operative.
Secondly, the remainder of the children were given a series of tests to measure memory and general mental capabilities and found to be having poor memory.
