Assessing Multimedia Exposure to Municipal Waste Incinerators Through Modeling and Monitoring. Sharon McCarthy, Gradient Corporation, 44 Brattle St., Cambridge, MA 02138
Risk Assessments are often based on the use of predictive models for exposure---point concentrations, but there have been few attempts to examine the predictions in a real-world context. Between October, 1987 and February, 1989, air, water, soil, and produce were sampled for As, Cr, Be, Cd, Pb, Ni, Hg, PCBS, B(a)P, and dioxins/furans as part of an USEPA study to determine the impacts from the Rutland, Vermont, Municipal Waste Combustor (MWC). The EPA results could not demonstrate an impact from the MWC, primarily due to analytes being present at concentrations below the limits of detection (especially in air samples) and analytes being present at concentrations within background variability (especially for soil data). In our analysis, we reviewed EPA's Rutland MWC study and recommended approaches and methods, for future studies, that would generate more constructive information regarding the assessment of MWC impacts on environmental media. Our analysis covered several different aspects of the Rutland MWC study, including: (1) evaluating additional tracers of MWC emissions, (2) performing air quality modeling and deposition modeling, and (3) determining the feasibility of conducting biomonitoring in humans for exposure to MWC emissions. Two additional compounds, zinc, and tin, were identified as possible tracers of MWC emissions. The air quality modeling results, predicted that the annual average concentrations, even at the point of maximum impact, were at or below the analytical detection limit for all compounds except dioxins and furans. Using the maximum deposition rate, we calculated it would take 100 years to double ' background soil concentrations for most toxic metals. We concluded that it is not feasible to perform biomonitoring to assess exposure in humans. For dioxins and furans, human exposure is dominated by sources other than the MWC. Calculations show that air concentrations of arsenic would have to be six orders of magnitude higher than those predicted by the dispersion modeling in order to be above the detection limit for arsenic in urine. A three tier approach to determining the impacts of a MWC in future studies is developed.