Human exposure to pollutants in the air, water, soil and food-whether in the form of short-term, high-level, or long-term, low-level exposure-is a major contributor to increased morbidity and mortality. However, the disease burden attributable to these exposures is not known with any degree of certainty because levels of general environmental pollution fluctuate greatly, methods for analysing the relationships are incompletely developed, and the quality of available data is generally poor. Precise measures of the association between pollution levels and health outcomes are therefore rare. Exposure to environmental pollution is also usually involuntary. People may be unaware of this and/or its possible effects; as a result they may exert little control over their risk of exposure. Biological and chemical agents in the environment are nevertheless responsible for the premature death or disablement of millions of people worldwide every year (WHO, 1992). It has recently been estimated that almost one quarter of the global burden of disease is attributable to environmental factors (WHO, 1997). This estimate, which is based on published data (Murray and Lopez, 1996), was made by attributing an environmental causal fraction to each disease category with a known environmental link. The ability to link health and environmental data, and thereby to determine the relationship between levels of exposure and health effects, is clearly vital to control exposure and protect health. Decision-makers need information on the health effects attributable to environmental pollution in order to assess the implications of their decisions, to compare the potential effects of different decisions and choices, and to develop effective prevention strategies.
Standards and guidelines against which to assess levels of environmental pollution are now widely available. For example, the World Health Organization (WHO) has developed environmental quality guidelines for various pollutants in the air (WHO, 1987), drinking-water (WHO, 1993),
*This chapter was prepared by C. Corvalán, T. Kjellström, G. Zielhuis and D. Briggs