Probabilistic Methods to Estimate Potential Exposures of Endangered Species to Incinerator Emissions. W. R. Alsop, G. R. Vishwanath, and P. J. Sheehan, ChemRisk Division, McLaren/Hart, Alameda, CA
Probabilistic methods, such as Monte Carlo analysis, provide an excellent means of quantifying uncertainties in estimates of chemical exposures to threatened or endangered wildlife populations. This approach has been used effectively, for example, to evaluate exposures of endangered species that may be foraging in areas potentially impacted by emission of a proposed incinerator. Bald eagle and peregrine falcon foraging activities in the area surrounding the proposed incinerator were modeled based on the data available on appropriate habitat for these species and reported observations of them in the surrounding area. These modeling efforts use available data on migration patterns to estimate portions of the year spent in potentially affected areas. The diets of both the bald eagle and peregrine falcon are modeled based on published data of prey preference as a proportion of diet and predicted distributions of chemical concentration in fish and terrestrial mammal prey species in the vicinity of the proposed incinerator. Because there are no current site-specific data, the modeling will account for uncertainties in chemical concentrations in prey species, in foraging patterns, and in exposure assumptions for the receptor species. The distributions of average daily dose (ADD) of chemicals associated with the consumption of fish, terrestrial mammals, and small birds were calculated from the exposure parameter distributions using Monte Carlo methods. The exposure distributions for chemicals were compared with relevant toxicity reference values to estimate risks to the endangered species population and the uncertainties associated with these risk estimates.