Acute toxicity of copper. Acute freshwater copper toxicity data were available for 121 species, primarily benthos and fish. Hardness data were available for 73 species, and the distribution of these data is presented in Figure 2. The range of acute toxicity values was from 1.3 mg/L for Daphnia to 13,000 mg/L for an aquatic sowbug . Within the fish trophic group, the Cyprinidae and Salmonidae families contained species that were more sensitive to acute copper exposures than the other eight families of freshwater fish. The benthic species most sensitive to acute copper exposure was gastropods, followed by amphipods. Despite the variability in sensitivities of the various species and trophic groups, the acute freshwater 10th percentile values for all species together (8.3 mg/L) and by trophic group (6.9–10.8 mg/L) were somewhat similar, as shown in Table 3