Implementation of the Exposure Model for Ecological Soil Screening Levels for Wildlife. J. A. Burris, Syracuse Research Corporation; B. E. Sample, CH2MHill; S. Ells, US Department of Energy, DC; and J. Bascietto, US Environmental Protection Agency
A modeling approach used for estimating contaminant concentrations in soil protective of terrestrial wildlife receptors. A wildlife Eco-SSL is the concentration of a contaminant in soil where the exposure equals the no-effect dose or toxicity reference value (TRV). Expression of the Eco-SSL for wildlife differs from that for soil biota. Whereas exposure and effects for soil biota are expressed as contaminant concentrations in soil, exposures and effects for wildlife are expressed as doses (mg contaminant/kg body weight/day). Estimates of dose are based on chemical-specific soil-biota uptake models, allometric food ingestion rate models, and soil ingestion rate models which are compared to respective TRVs. Although the modeling approach is deterministic, values for input parameters were developed using probabalistic methods. The model was paramaterized for three avian and three mammalian receptors, each representing insectivore, carnivore, and herbivore feeding guilds. The presentation focuses on the implementation of these models for several soil contaminants (e.g., Pb, DDT, dieldrin, Co, Sb, Cr). Sensitivity analyses examine the parameters of the exposure model and Eco-SSL calculation that most influence the final value. The Eco-SSL model was iteratively solved by varying values for each input parameter over their full range, while holding all other parameters constant at the value used to calculate the Eco-SSL. Parameters for the final wildlife Eco-SSL model was accomplished by selecting a combination of conservative and central tendency values from distributions for the different parameters. The TRV was the most influential value, followed by soil-plant or soil-earthworm bioaccumulation factors, and food ingestion rate. Surprisingly, soil ingestion was among the least influential values. In models in which log-linear regression models were used, variation in the slope and intercept had comparatively little influence on the final Eco-SSL value.
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