Physiologically based assessment of human exposure to urban air pollutants and its significance for public health risk evaluation.

Exact measurements or modeling of human exposures to environmental pollutants are of crucial importance for a realistic evaluation of public health risks. Current concepts, however, often use assumptions that result in overly conservative assessments of public health risks. Too frequently the dose of the pollutant retained in the body is approximated by oversimplified predictions assuming that all that is inhaled remains in the organism, that pollutant concentrations in various microenvironments are identical to those recorded by remote monitors, that the residence indicates the site where people spend all their time, and that the urban population is continuously exposed to outdoor air for 24 hr/day and 70 years/lifetime. The review shows that in intermittent exposures only a fraction of inhaled toxicants remains in the body, that pollutant concentrations differ largely from one microenvironment to another, and that human activity patterns must be incorporated in every realistic exposure assessments. Specifically, the probability of being exposed to a short peak of ozone is predetermined in variable urban concentrations primarily by the coincidence of exercising outdoors at the time and site of elevated ozone levels. When combined with a physiologically based exposure evaluation, this probabilistic approach provides a scientifically sound estimate of actual occurrences of adverse exposures and a realistic assessment of potential health hazards.