New pollutants

Reports that indicate a rising concentration in the atmosphere of volatile organic compounds (VOCs) like benzene, toluene, butadiene and others, are as revealing as they are alarming. They signal a marked change in the profile of air pollution, which is potentially more dangerous for human beings and vegetation than the usual pollutants, both gaseous and particulate matter. VOCs can affect the respiratory system, besides damaging the liver, kidney and nervous system. Some VOCs are known to cause cancer as well. Studies in Delhi showed benzene concentration to be as high as 34 to 47 mg per cubic metre of air at different places towards the end of last month. This is several times higher than the tolerable levels. What is worse, these volatile organics tend to produce ozone through chemical reactions with oxides of nitrogen in the presence of sunlight. As a result, the concentration of ozone, a respiratory toxicant, is also rising menacingly. While it is true that ozone is necessary in the upper atmosphere as it shields the earth from the sun's harmful ultraviolet radiation, its presence in high doses near the earth's surface is dangerous for the health of both human beings and vegetation. Plant scientists who attended the International Rice Congress, held in Delhi recently, confirmed the adverse effects of higher surface level ozone, including on wheat and soybean. Ozone is also a major component of smog which, besides being injurious to health, has been observed in recent years to cause civic problems, including the disruption of air, rail and road traffic.

An equally disquieting aspect of VOC-induced change in the pollution scenario is that people are as unsafe indoors as outdoors. The concentration of some organo-carbon compounds tends to be up to five and ten times higher indoors than outdoors. This is because VOCs are spewed from a variety of sources, including automobiles, paints and lacquers, building material and furnishings, adhesives and even office equipment such as copiers and printers. Dry-cleaning activity is one of the major sources of the new air pollutants. Perchloroethylene, used quite widely for this purpose, has been found in laboratory studies on animals to be carcinogenic. And, of course, people tend to inhale different levels of this chemical in homes where dry-cleaned clothes are stored, as also while wearing them. The other significant sources of pollutants include the material used in road construction and liquid petrol and crude oil. That is why the concentration of VOCs is usually higher on roads and near petrol stations. Though India has gone ahead and introduced unleaded petrol, the aromatic content of petrol, including its benzene level, is still quite high.

The country still does not have air quality standards pertaining to VOCs. In fact, there are no universally accepted international standards for them. Nor is there any concrete global drive to keep VOC emissions in check. An international protocol was inked way back in 1991 on long-range, trans-boundary air pollution caused by VOCs but this has remained confined largely to the European countries.