PARENT SESSION
Oral Session #67: Ecotoxicology and Applied Ecology.
Presiding: W. Snyder
Wednesday, August 7. 1:00 PM to 4:45 PM. Cochise Meeting Room, TCC.
Treatment of uncertainty in ecological soil screening levels for wildlife.
REGAN, HELEN*,1, SAMPLE, BRAD2, FERSON, SCOTT3, 1 National Center for Ecological Analysis and Synthesis, Santa Barbara, CA2 CH2M HILL, Sacramento, CA3 Applied Biomathematics, Setauket, NY
ABSTRACT- The first step in remediation and restoration of contaminated sites is the identification of chemicals of potential concern. The U.S. EPA is sponsoring development of Ecological Soil Screening Levels (Eco-SSLs) for terrestrial wildlife at Superfund sites. Eco-SSLs represent concentrations of contaminants in soils that are believed to be protective of ecological receptors. A conservative exposure model, based on soil and food ingestion rates, and bioaccumulation factors, has been developed for estimation of wildlife Eco-SSLs. It uses a hazard quotient which is constrained between 0 and 1. Eco-SSLs are calculated for two species for lead and DDT using deterministic and probabilistic methods, in particular, a method for bounding probability distributions when data is limited. In this talk we examine the extent to which these Eco-SSLs are conservative and protective, how parameterization of the model influences the resulting Eco-SSLs, and how the treatment of uncertainty impacts results. Conclusions obtained include: the use of central-tendency point estimates may result in hazard quotients much larger than one; if no hazard quotients larger than one are allowed, any probabilistic approach is identical to a worse-case approach; the larger the uncertainty about inputs, the smaller the Eco-SSL must be. This is the inherent cost of uncertainty. We show how probability bounds analysis can be used to improve the reliability and protection of Eco-SSLs.
KEY WORDS: probabilistic risk assessment, soil contamination, ecological soil screening levels, probability bounds