Though take a pro­longed study to reveal it.

Though no accurate quantitative information exists, a number of relatively well-defined syndromes, caused by particular substances, are known and, in general, the fact that health may be diminished by living in an area of substantial industrial pollution has been established. To put this in perspective, it should at once be pointed out that, in statistical terms, the effects on mortality is minor compared with the damage done by the motor car and the cigarette. The reason that no formal estimate of effects of pollution on health can be given lies in the complexity of population, the varying exposure and response of the individuals at risk, and the difficulty of proving cause and effect. A relatively straightforward illustration of this is the need to conduct elaborate surveys to determine the side-effects of therapeutic drugs, where one is testing the reaction of humans to strict doses of defined chemicals, under relatively standard conditions. If an effect takes some time to develop or only occurs in a minority of eases, it may take a pro­longed study to reveal it. When one looks at a more complex case, demonstration becomes even more difficult.

For example, it has long been believed that cigarette smoking is bad for lungs. It has, however, taken elaborate statistical investigation to prove that there is a strong link between smoking and lung cancer. Even now there is considerable uncertainty about which of the possible carcinogens, in a cigarette is most harmful. Similarly, when one takes environmental variables, often they, poorly quantified, it becomes even more difficult to prove an effect. However, even if we cannot always calculate total damage, a number of ‘pollution syndromes’ is known and precautions may be taken accordingly. Those who are at risk to pollutants fall into three main categories: those who are ex­posed to the highest concentrations, those who have impaired heal and the very young. The highest concentrations of pollutants are commonly found at their source, and so work­ers in the industries concerned are most likely to suffer ill effects. It is, indeed, by examining occupational associations of disease that suspicion may first be aroused One of the first such cases was noticed by Sir Percival Pott in 1775, when he noticed that chimney sweeps were especially prone to develop cancer of the scrotum.

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In those days, chimney sweeps suffered long exposure to soot, frequently hot soot, under conditions which allowed little hygiene. Since then, many other occupational cancers have been discovered among work­ers, for example, tar, and shale-oil and asbestos industries and in factories where workers suffer prolonged contact with certain kinds of lubricating oils. Lest it be presumed that such risks are totally remote from any general problem of effluent control, it may be pointed out that only recently has skin cancer been found among gardeners, apparently caused by the habit of spreading soot by hand. Industrial illnesses are carefully investigated then, not only to protect workers, but also to prevent their products or wastes from threatening other mem­bers of the population. A second group, at risk, consists of those who are, in some way, less fit. During the heavy London fogs that are now happily infrequent, it was found that mortality and sickness rates increased dramatically. Those affected were mostly the old or the ill.

Similarly, it was noted that those suffering from the heart disease ‘angina’ were liable to deteriorate if ex­posed to the smog-laden atmosphere of a Los Angeles freeway. In the same environment, when assured a supply of uncontaminated air, they remained in relatively good health. The control of general industrial smoke and car exhaust pollution, then, can be justified, in particular, on grounds of protection of the ill, and in general, for the rest of the population on whom there may be lesser effects.

The young, too, are especially at risk from pollution. Many noxious substances greatly affect rapidly growing and developing tissues, particularly of the yet unborn child. Al­though the absolute threshold levels, for the poisoning by heavy metal, have not been deter­mined, it is clear that the required doses are less for children than for adults, and the effects are much more likely to be permanent. Also, if an environmental hazard takes some time to manifest its effects, the young are clearly those most at risk. When there is a long latent period, the elderly are hardly in danger, but tine young are, since they alone will live long enough to develop the syndrome.


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