APPLICATION OF A PREDICTIVE APPROACH TO ESTIMATE EXPOSURE TO NONSMOKING URBAN SUBPOPULATIONS TO BACKGROUND LEVELS OF BENZENE IN ONTARIO

An indirect approach was used to estimate exposure to background level s of atmospheric benzene for a selection of Ontario non-smoking urban subpopulations. Activity codes obtained from nationally representative time-budget surveys were allocated to five general microenvironments (home, work (or school), outdoors, commuting, and other indoors) and f urther combined with inhalation rates corresponding to specific levels of physical activity in order to develop average activity patterns fo r six sub-populations believed to be differently exposed to atmospheri c benzene in urban areas (children, teenagers, office workers, outdoor workers, transit workers, and seniors). These activity patterns were then combined with representative concentrations of benzene measured i n the selected microenvironments in Ontario in order to evaluate expos ure. Two metrics were used for this purpose, integrated exposure and p otential average daily dose (intake). Potential lifetime average daily doses were also estimated for three composite subgroups representing average office, outdoor, and transit workers. A probabilistic approach using a Monte-Carlo sampling procedure was used in order to estimate possible ranges of exposures experienced by the various sub-population s, Results obtained suggested that the highest daily integrated exposu re (mean: 131 mu g-hrs/m(3)) was associated with the average transit w orker while comparable levels were estimated for the other sub-populat ions investigated (mean: 77-86 mu g-hrs/m(3)). These levels correspond ed to 24-hours time-weighted average (TWA) -equivalent concentrations of 5.5 mu g/m(3) and 5.5 mu g/m(3), respectively. Statistical distribu tions of integrated exposures obtained with the probabilistic approach indicated levels as high as 343 mu g-hrs/m(3) (97.5th percentile) in the case of the average transit worker, corresponding to TWA-equivalen ts in excess of 15 mu g/m(3) When levels of physical activities and in halation rates were integrated in the calculation of exposure, the hig hest potential average daily dose was found to be associated with the average child (mean: 3.1 mu g/kg-day; 97.5th percentile: 6.0 mu g/kg-d ay) whereas comparable amounts were estimated for teenager and transit workers (mean: 2.1 CI mu g/kg-day; 97.5th: 4.1 and 6.9 mu g/kg-day, r espectively). Indoor microenvironments (home, office/school, other ind oors) were identified as the major contributors to total exposure and intake of benzene (greater than or equal to 50%) although their relati ve importance varied depending on the exposure metric utilized. Potent ial lifetime average daily doses estimated for transit workers varied from 2.1 (mean) to 5.4 (97.5th) mu g/kg-day. This was slightly higher than those estimated for the average office and outdoor workers (mean: 1.5-1.7 mu g/kg-day). These projections suggest that average non-smok ing children and teenagers are the most exposed sub-populations among those investigated to background levels of atmospheric benzene as a re sult of their daily activities. However, these projections must be int erpreted with caution in view of uncertainties associated with some of the assumptions adopted, the limited database used to document benzen e levels, and as a result of unaccounted sources of emissions which, u nder certain circumstances, can significantly modify these conclusions .