AN APPROACH TO QUANTIFYING SPATIAL COMPONENTS OF EXPOSURE FOR ECOLOGICAL RISK ASSESSMENT

Estimating ecological risks associated with contaminants in the enviro nment requires accurate characterization of the exposure of organisms to potentially toxic materials. Because organisms integrate contaminan t exposure over space and time, estimating exposure concentrations ref lective of actual exposures is a complex task. Quantification of spati al components of environmental exposure can utilize computerized Geogr aphic Information Systems (GIS) as a central tool. The GIS was used to evaluate ecological risks to terrestrial receptors at a National Prio rities List (NPL) site where dieldrin was one of the contaminants. The GIS was applied directly to estimating spatially weighted exposure co ncentrations within organisms' foraging, or exposure ranges. Moreover, GIS was also used for comparing exposure concentrations to ''benchmar k'' concentrations and subsequent presentation of the results in a thr ee-dimensional ''risk surface'' format. The three-dimensional risk sur faces were then superimposed on site-specific maps to serve as effecti ve visual representations of site-specific quantified ecological risks and, as such, provide an effective risk-management decision-making to ol. As an integral part of this approach, GIS serves as an interactive tool for assessing the effectiveness of proposed remedial alternative s by facilitating evaluation of effects of various remediation scenari os. This capability can be used to optimize remedial costs, benefits, and impacts.