Uncertainty analysis of regional mercury exposure

A modeling system has been developed to simulate regional environmental exp osure to mercury due to atmospheric deposition of mercury to watersheds. Th e atmospheric fate and transport of mercury is simulated using a comprehens ive three-dimensional Eulerian model, the Trace Element Atmospheric Model ( TEAM). The aquatic chemistry and bioaccumulation of mercury in fish are sim ulated using a model of mercury cycling in a lake/watershed system, the Reg ional Mercury Cycling Model (R-MCM). Fish consumption was derived from a re view of available surveys. Previous work focused on an assessment of the en vironmental and inter-individual variability in key input data (Seigneur et al., 1997a). We address here the uncertainties associated with critical mo del input variables (e.g., atmospheric deposition velocities, precipitation rate, limnological characteristics). A probabilistic assessment is conduct ed to propagate the uncertainties in the input data through the modeling sy stem and develop a probability distribution of the human mercury dose that reflects these uncertainties. The standard deviation of the distribution of the calculated human dose is about 50% of the mean value. For the example considered here (i.e., Park Lake in Michigan, U.S.A.), 80% of the uncertain ty in the human dose was due to uncertainties in the speciation of mercury air emissions, pH and temperature of the lake, burial velocity of the sedim ents, and rate of fish consumption.