The New Straits Times, October 12, 1998
In conjuction with the coming Environmental Week (Oct 21-27), it is good to acknowledge that from Oct 1, chlordane - a chemical used mainly by pest control companies for the treatment of termites - has been banned. This was announced by the Malaysian Pesticide Board recently.
This move is indeed appropriate since the US Environmental Protection Agency banned the chemical 10 years ago. substance is known for its hazardous effects, both short- and long-term.
The ban on the manufacture and importation of chlordane however has also raised some larger questions. Chlordane belongs to a group of chemicals generally known as persistent organic pollutants or POPs for short.
They include similar organochlorine compounds like DDT, PCBs, furans, heptachlor, aldrin, dieldrin and endrin. Some of these are still commonly found in Malaysia. Many of them are used in or arise from industry, agriculture and disease vector control.
They may also be created unintentionally as by-products. Because of their persistent nature, over a period of time, their concentrations can increase to levels that can eventually cause health effects.
The best known example is perhaps DDT, which has been widely used for vector control for years. It has a low acute toxicity in humans and for a while was regarded as 'safe'. However, it is now recognised that DDT has a number of long-term side effects, including acting as an "endocrine disruptor", namely in mimicking steroid hormones in the human body.
Moreover, the reports of high concentrations of DDT found in human breast milk, especially in developing countries, point to the possibility of environmental accummulation of DDT.
One prospective study, based on the New York University Women's Health tudy, showed a significant association between body stores of the DDT metabolite, DDE and breast cancer. On the other hand, endrin is even more hazardous.
As a comparison, it is reported to be between two to four times more toxic than DDT (LD 50: 16-43 mg/kg in rats), despite it being more readily metabolised. Food contaminated with endrin has caused several clusters of illness worldwide, especially with regard to poisoning in children.
But these are often overlooked because the symptoms resemble those of encephilitis, making the cause not immediately apparent.
Yet another group of hazardous chemicals is the polychlorinated biphenyls (PCBs), which has been around since 1929 but was banned more that 20 years ago in the US. PCBs are made up of more than 200 related compounds, which, because of their many ideal characteristics, are used in many industrial applications, especially as insulators.
The extent to which PCBs can affect us cannot be overemphasised since, up to the time of their discovery as environmental and health hazards, they had been produced and used extensively for more than three decades.
Like most POPs, PCBs too can accumulate in the fatty tissue and over the years, PCBs have been detected in food samples. The higher the level of the food chain, the greater the concentration of PCBs. Some have been passed on to eggs (for birds and fishes) as well as milk (for mammals), and eventually to humans.
Indeed, PCBs can be traced to humans through the consummation of contaminated food and through breast milk in the case of infants. One report submitted to the UK Department of Health stated that "breast-fed infants are receiving up to 17 times the tolerable amounts of dioxins and polychlorinated biphenyls (PCBs)."
One of the most alarming exposure effects of PCBs is the lowering of the IQ level. It was recently confirmed that children exposed to low levels of PCBs in the womb will grow up with low IQs, poor reading comprehension, attention-deficit and memory problems.
Even at the age of 11, maternal exposures to PCBs were correlated with lower overall IQ and lower verbal IQ score. About 11 per cent of the children whose mothers had high exposure to PCBs now have IQs of 6.2 points lower than average. Other researchers suggested that PCBs interfere with the thyroid hormones, which are essential for the development of the brain.
Children exposed to PCBs in the womb at levels regarded as "background levels" in the US have also been reported to experience the loss of muscle tone, poor reflexes at birth, delays in psychomotor development from the ages of six to 12 months, and diminished visual recognition memory at seven months. Other findings include "balky, uncooperative behaviour".
All these invariably are related to the presence of PCBs in the environment -- be it in storage, landfills, sediment of lakes, rivers or even oceans -- apart from the 70 per cent that are in use.
Given all these findings, it is therefore not suprising that a ban was imposed on PCBs -- outlawing the manufacture, sale and distribution -- by the US Congress as early as 1976, except in "totally enclosed" systems. Even then, although the use of PCBs in heat transfer and hydraulic systems can be regarded as "closed", there is always the risk of leakage and exposure.
Thus, while the banning of chlordane can be seen as a step in the right direction, it is by not means the only substance of concern. We must continue to weed out as many POPs as possible in the shortest time frame until they no longer pose potential risks to the population.
In fact, in a recent WHO report (1997), which was part of the review five years after the Earth Summit, considerable attention was given to POP. The report commented that the use of such substances cannot be considered sustainable. Increasing evidence of the long-range transport in the environment of these substances and the consequent threats they pose has prompted the international community to call for urgent global action to reduce and eliminate the releases and emissions of these chemicals.
Among the 12 POPs under initial consideration for international action, DDT is the only insecticide still in use for public health purposes, notably vector control. DDT has had a major impact on the eradication or virtual eradication of malaria from a number of countries, including Malaysia.
Even then, its use has declined following development of vector-resistance, reduction in its global production and adverse recent findings. In other words, POPs are fast losing their "popularity" and Malaysians should be spared of any potential hazards that could arise from accessibility to such substances.
The environment and health dangers of POPs
