ESTIMATING EXPOSURE AND DOSE TO CHARACTERIZE HEALTH RISKS - THE ROLE OF HUMAN TISSUE MONITORING IN EXPOSURE ASSESSMENT

Exposure assessment is an integral part of health risk characterizatio n. Exposure assessments typically address three critical aspects of ex posure: the number of people exposed to the environmental toxicant, at specific concentrations, for the time period of interest; ?he resulti ng dose; and the relative contribution of important sources and pathwa ys to exposure/dose. Because historically both ''point-of-contact'' me asurements and information about dose and related pharmacokinetic proc esses have been lacking, exposure assessments have had to rely on cons truction of ''scenarios'' to estimate exposure and dose. This could ch ange, however, as advances in development of biologic markers of expos ure and dose make it possible to measure and interpret toxicant concen trations in accessible human tissues. The increasing availability of ' 'biomarkers,'' coupled with improvements in pharmacokinetic understand ing, present opportunities to estimate (''reconstruct'') exposure from measurements of dose and knowledge of intake and uptake parameters, H uman tissue monitoring, however, is not a substitute for more traditio nal methods of measuring exposure, but rather a complementary approach . A combination of exposure measurements and dose measurements provide s the most credible scientific basis for exposure assessment.