A comparison of acute and chronic toxicity methods for marine sediments.

Sediment toxicity tests are valuable tools for assessing the potential effects of contaminated sediments in dredged material evaluations because they inherently address complexity (e.g., unknown contaminants, mixtures, bioavailability). Although there is a need to understand the chronic and sublethal impacts of contaminants, it is common to conduct only short-term lethality tests in evaluations of marine sediments. Chronic toxicity methods for marine sediments have been developed but the efficacy of these methods is less documented. In this evaluation of marine sediments collected from the New York/New Jersey (NY/NJ) Harbor, three 10-d acute toxicity test methods (Ampelisca abdita, Leptocheirus plumulosus, Americamysis bahia) and three chronic and sublethal test methods (28-d L. plumulosus, 20- and 28-d Neanthes arenaceodentata) were applied by three testing laboratories. Although the N. arenaceodentata and A. bahia tests did not indicate significant toxicity for the sediments tested in this study, these methods have been reported useful in evaluating other sediments. The 10-d A. abdita, 10-d L. plumulosus and 28-d L. plumulosus tests were comparable between laboratories, indicating 29-43%, 29%, and 43-71% of the tested sediments as potentially toxic. The 28-d L. plumulosus method was the only chronic toxicity test that responded to the test sediments in this study. The 28-d L. plumulosus endpoint magnitudes were related to sediment chemistry and the sublethal endpoints were reduced as much or more than acute lethality endpoints. However, intra-treatment sublethal endpoint variability was greater, compromising detection of statistical significance. In this study, the chronic L. plumulosus test method was less consistent among laboratories relative to acute test methods, identifying potential for toxicity in a similar number (or slightly more) NY/NJ Harbor sediments.

A methodology for deriving tissue residue benchmarks for aquatic biota: a case study for fish exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin and equivalents.

Tissue residue-based toxicity benchmarks (TRBs) have typically been developed using the results of individual studies selected from the literature. In the past, TRBs have been developed using a point estimate (e.g., LC50 value) reported in a study on a single species deemed to be most closely related to the receptor of interest. Despite attempts to maximize the protectiveness and relevance of TRBs, their relationship to specific receptors remains uncertain, and their general applicability for use in broader ecological risk assessment contexts is limited. This article proposes a novel framework that establishes benchmarks as distributions rather than single-point estimates. Benchmark distributions allow the user to select a tissue concentration that is associated with the protection of a specific percentage of organisms, rather than linked to a specific receptor. A methodology is proposed for searching, reviewing, and analyzing linked, tissue residue effect data to derive benchmark distributions. The approach is demonstrated for contaminants having a dioxin-like mechanism of toxic action and is based on residue effects data for 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and equivalents in early life stage fish. The calculated tissue residue benchmarks for 2,3,7,8-TCDD toxic equivalency (TEQ) derived from the resulting distribution could range from 0.057- to 0.699-ng TCDD/g lipid depending on the level of protection needed; the lower estimate is protective of 99% of fish species whereas the higher end is protective of 90% of fish species.