TOXICOLOGICAL BENCHMARKS FOR SCREENING CONTAMINANTS OF POTENTIAL CONCERN FOR EFFECTS ON FRESH-WATER BIOTA

An important early step in the assessment of ecological risks at conta minated sites is the screening of chemicals detected on the site to id entify those that constitute a potential risk. Part of this screening process is the comparison of measured ambient concentrations to concen trations that are believed to be nonhazardous, termed ''benchmarks.'' This article discusses 13 methods by which benchmarks may be derived f or aquatic biota and presents benchmarks for 105 chemicals. It then co mpares them with respect to their sensitivity, availability, magnitude relative to background concentrations, and conceptual bases. Although some individual values can be shown to be too high to be protective a nd others are too low to be useful for screening, none of the approach es to benchmark derivation can be rejected without further definition of what constitutes adequate protection. The most appropriate screenin g strategy is to use multiple benchmark values along with background c oncentrations, knowledge of waste composition, and physicochemical pro perties to identify contaminants of potential concern.