Development of a Modeling Approach for Ecological Soil Screening Levels for Wildlife. B. E. Sample, CH2M HILL; J. Bascietto, U.S. DOE; S. Ferson, Applied Biomathematics; R. Ryti, Neptune and Co.; and J. Yurk, US EPA
Expression of exposure and effects for wildlife differs from that for soil biota. Whereas exposure and effects for soil biota are expressed as chemical concentrations in soil, exposure and effects for wildlife are typically expressed as dosages in mg contaminant/kg body weight/day. Effects are evaluated by comparing exposure to toxicity reference values (TRVs) from laboratory studies, with exposure models are used to generate exposure estimates. A modeling approach for estimating contaminant concentrations in soil that are protecting of terrestrial wildlife receptors was developed as part of a collaborative effort involving government, industry, and academic representatives. The model incorporates chemical-specific soil-biota uptake models, allometric food ingestion rate models, and soil ingestion rate models to estimate and compare contaminant exposure to an appropriate TRV. Although the modeling approach is deterministic, values for input parameters in the model were developed using probabalistic methods such that a consistent and known degree of conservatism in soil screening levels could be assured. The model was paramaterized for three avian and three mammalian receptors, each representing insectivore, carnivore, and herbivore feeding guilds. Once a screening value is calculated for all six species for a given chemical, the lowest value is selected as the wildlife EcoSSL.
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