AMBIENT AIR-POLLUTION EXPOSURE AND CANCER

Epidemiologic evidence on the relation between ambient air pollution e xposure and cancer is reviewed. The well-documented urban/rural differ ence in lung cancer incidence and the detection of known carcinogens i n the atmosphere gave rise to the hypothesis that long-term exposure t o air pollution may have an effect on lung cancer risk. However, probl ems inherent in assessing adequately the exposure of interest led to c onsiderable difficulties in evaluating this effect. Routinely measured air pollutants do not include, as a rule, established carcinogens, an d air pollution measurements usually come from fixed-site monitors, ma king it difficult to estimate individual exposures, especially long-te rm. The nature of the exposure and associated measurement problems mad e ecologic comparisons a natural way to approach the study of air poll ution effects on lung cancer risk. The descriptive/ecologic studies wh ich have been undertaken after 1950 often had problems with inadequate control of confounding, but, on the whole, provided evidence compatib le with the hypothesis that urban and industrial air pollution may hav e an effect on lung cancer risk. The results of several case-control a nd cohort studies are described in the present review with emphasis on the exposure metric used. These studies, which control for important potential confounders, suggest that urban air pollution may be a risk factor for lung cancer, with estimated relative risks in the order of up to about 1.5 in most situations.