Determination of a Tissue and Sediment Threshold for Tributyltin (TBT) to Protect Prey Species of Juvenile Salmonids Listed Under the Endangered Species Act

摘要

The purpose of this report is to determine the concentrations of tributyltin (TBT) in sediment that would be protective against adverse effects in prey species of salmonids listed under the Endangered Species Act (ESA). Two approaches for determining adverse sediment concentrations due to TBT contamination are presented here. The first is the equilibrium partitioning (EqP) approach, which relies on a sediment-water partition coefficient and toxicological data for water exposures. The EqP approach utilizes the large water-quality database that has been generated over the last two decades for TBT and provides strong evidence for adverse effects at low-exposure concentrations (Weston 1996). The second approach involves determination of a TBT tissue residue that is considered harmful for most species, which is then used to predict the sediment concentration that would likely produce this adverse tissue concentration. Both approaches are presented here because they generally support each other. Based on the information presented in this document, and the inherent difficulty in measuring porewater concentrations, the tissue residue approach is the recommended method for determining adverse sediment concentrations. Using this analysis, the protective sediment concentration for TBT proposed here is 6,000 ng/g organic carbon.