Comparative risk assessment: an international comparison of methodologies and results

Comparative risk assessment (CRA) is a systematic procedure for evaluating the environmental problems affecting a geographic area. This paper looks beyond the U.S. border and examines the experience with CRAs conducted in various developing countries and economies in transition, including Bangkok, Thailand, Cairo, Egypt and Quito, Ecuador, as well as other locations in Eastern Europe, Asia and Central and South America. A recent pilot CRA conducted in Taiwan is also considered. Comparisons are made of both the methodologies and the results across the relatively diverse international literature. The most robust finding is that conventional air pollutants (e.g., particulate matter and lead) consistently rank as high health risks across all of the CRAs examined. Given the varied nature of the settings studied in the CRAs, including level of economic development, urban-rural differences, and climate, this finding is particularly significant. Problems involving drinking water are also ranked as a high or medium health risk in almost all the countries studied. This is consistent with the results of analyses conducted by the World Bank suggesting contamination, limited coverage and erratic service by water supply systems. Beyond the major air pollutants and drinking water, the CRA results diverge significantly across countries. A number of problems involving toxic chemicals, e. g., hazardous air pollutants, rank as high health risks in the US but do not appear as consistent areas of concerns in the other countries studied. This likely reflects the so-called "risk transition" - the shift from sanitation and infection disease problems to those involving industry, vehicles and toxic substances - that often occurs with economic development. It may also reflect the greater information about sources of toxic pollutants in the U.S. For other problems, there are important differences across the developing countries and economies in transition. For example, hazardous and (industrial) non-hazardous waste issues ranked as medium or low health risks in all the countries studied, except for Taiwan where unmanaged toxic waste sites were considered to pose high risks. While the generally low ranking is consistent with the notion that few people are directly exposed to hazardous and (industrial) non-hazardous waste, it is not entirely surprising that views might be different in Taiwan, where space is so limited and population density is so high. We suggest that the wide range of findings likely reflect genuine differences among the countries studied. However, we cannot entirely rule out the possibility that some of the observed similarities (and differences) arise from the (relatively) common methodologies employed.