Using Toxicity Identification Evaluation (TIE) Methods to Investigate Causes of Sediment Toxicity to Amphipods

2 Executive Summary More than 25 years of monitoring studies have shown widespread sediment toxicity in the San Francisco Estuary. While toxicity is generally persistent, patterns of sediment toxicity demonstrate temporal and spatial variability, with greater toxicity observed in samples collected during the rainy winter season at sites near the mouths of tributaries. Samples collected as part of the Regional Monitoring Program's Status and Trends program consistently show significant but moderate levels of toxicity at many stations. A number of studies have shown that amphipod mortality in laboratory tests is correlated with several metal and organic chemical constituents in the Estuary's sediments. These studies have also demonstrated significant correlations between amphipod mortality and chemical mixtures. While correlative studies are useful, they do not provide direct evidence of the causes of sediment toxicity. Understanding the cause(s) of sediment toxicity is one of the primary goals of the RMP because management of contaminants entering the Estuary is most efficient when it targets the key chemicals responsible for biological impacts. One approach for determining the cause(s) of toxicity is the process known as Toxicity Identification Evaluation (TIE), which involves a series of procedures designed to decrease, increase, or transform the bioavailable fractions of sediment contaminants to assess their contributions to sample toxicity. TIEs have been used to show that divalent cations (e.g., copper) were responsible for toxicity to bivalves in sediment samples from the Estuary. To date, however, TIE methods have not been sufficiently developed to determine the causes of sediment toxicity to amphipods. With the recent development of new sediment TIE procedures, the RMP funded a TIE study designed to investigate causes of sediment toxicity in two samples collected during the rainy season from stations located near the margins of the Estuary. Based on historical data, twelve samples from previously toxic stations were selected for a screening survey, from which two stations were to be selected for TIEs. Toxicity of these sediments was tested with the amphipod Eohaustorius estuarius, the primary species used in the Status and Trends program, as well as the benchmark species used in the State of California's Sediment Quality Objectives program. Fourteen samples from twelve stations were surveyed, but only Mission Creek sediment was sufficiently toxic for use in a TIE (<50% survival). One station had poor sediment quality and could not be tested, and a thirteenth station was added in an effort to find another 3 significantly …