Application of a predictive approach to estimate exposure to non‐smoking urban sub‐populations to background levels of Benzene in Ontario

Abstract

An indirect approach was used to estimate exposure to background levels of atmospheric benzene for a selection of Ontario non‐smoking urban sub‐populations. 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 further combined with inhalation rates corresponding to specific levels of physical activity in order to develop average activity patterns for six sub‐populations believed to be differently exposed to atmospheric 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 in the selected microenvironments in Ontario in order to evaluate exposure. Two metrics were used for this purpose, integrated exposure and potential average daily dose (intake). Potential lifetime average daily doses were also estimated for three composite sub‐groups 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‐populations. Results obtained suggested that the highest daily integrated exposure (mean: 131 μg‐hrs/m3) was associated with the average transit worker while comparable levels were estimated for the other sub‐populations investigated (mean: 77–86 μg‐hrs/m3). These levels corresponded to 24‐hours time‐weighted average (TWA)‐equivalent concentrations of 5.5 μg/m3 and 3.5 μg/m3, respectively. Statistical distributions of integrated exposures obtained with the probabilistic approach indicated levels as high as 343 μg‐hrs/m3 (97.5th percentile) in the case of the average transit worker, corresponding to TWA‐equivalents in excess of 15 μg/m3. When levels of physical activities and inhalation rates were integrated in the calculation of exposure, the highest potential average daily dose was found to be associated with the average child (mean: 3.1 μg/kg‐day; 97.5th percentile: 6.0 μg/kg‐day) whereas comparable amounts were estimated for teenager and transit workers (mean: 2.1 μg/kg‐day; 97.5th: 4.1 and 6.9 μg/kg‐day, respectively). Indoor microenvironments (home, office/school, other indoors) were identified as the major contributors to total exposure and intake of benzene (≥50%) although their relative importance varied depending on the exposure metric utilized. Potential lifetime average daily doses estimated for transit workers varied from 2.1 (mean) to 5.4 (97.5th) μg/kg‐day. This was slightly higher than those estimated for the average office and outdoor workers (mean: 1.5–1.7 μg/kg‐day). These projections suggest that average non‐smoking children and teenagers are the most exposed sub‐populations among those investigated to background levels of atmospheric benzene as a result of their daily activities. However, these projections must be interpreted with caution in view of uncertainties associated with some of the assumptions adopted, the limited database used to document benzene levels, and as a result of unaccounted sources of emissions which, under certain circumstances, can significantly modify these conclusions.