AIR AND HEALTH Health effects of air pollution

One way of classifying the health effects of pollutants is to make a distinction between two broad categories: acute (i.e. short-term) and chronic (i.e. long-term) effects. For each of these categories, the effects can range in severity from death to minor illness or discomfort. For example, dust and other polluting particles in air can have acute effects, such as immediate irritations to eyes and throat, or hospitalisation and even deaths from respiratory failure or heart attacks, caused by severe episodes of air pollution. For some pollutants there may be a threshold level of exposure, below which no health effect is evident, e.g. SO2. For others, there may be no threshold, and some effect may occur whatever the level of exposure is, e.g. benzene.

In a given population, not all individuals are affected equally by the same environmental hazard. Substantial variations in sensitivity to an exposure may occur, due to age, nutritional status, genetic predisposition and state of general health, which are important determinants of individual vulnerability. Risk assessments need to be made for particular high-risk groups such as infants and young children, the elderly, pregnant women and their foetuses, the nutritionally deprived, and individuals suffering from some diseases. It is especially important to identify these high-risk groups because they will usually be the first to experience adverse health effects as the level of the pollutant increases. For example, a recent study showed higher values of lead in blood in children living near a lead smelter than in adults in the same area. Often, only a small subset of the population may experience high levels of exposure to air pollution, and the doses received by the general population are so low that only vulnerable high-risk groups are severely affected. Any excess mortality due to a pollutant may therefore be restricted to a small section of the population, so mortality rates for entire populations can often be weak and insensitive indicators of environmental health effects.

Estimates of health damage from air pollution are difficult to calculate. In a recent analysis of summer smog episodes in the UK, for example, the number of additional hospital admissions for respiratory disorders in the summer of 1993 was estimated to be around 180. This represents some 0.1% of all such hospital admissions in the UK during that period. There may also be estimations for smaller populations where the information on exposure to air pollution is more precise and underlying assumptions are more reliable.