Mercury toxicity to freshwater organisms: extrapolation using species sensitivity distribution

Mercury toxicity to aquatic organisms was evaluated in different taxonomic groups showing the following species sensitivity gradient: Daphnia magna > Daphnia longispina > Pseudokirchneriella subcapitata > Chlorella vulgaris > Lemna minor > Chironomus riparius. Toxicity values ranged from 3.49 μg/L (48 h-EC₅₀ of D. magna) to 1.58 mg/L (48 h-EC₅₀ of C. riparius). A species sensitivity distribution was used to estimate hazardous mercury concentration at 5 % level (HC5) and the predicted no effect concentration (PNEC). The HC5 was 3.18 μg Hg/L and the PNEC varied between 0.636 and 3.18 μg Hg/L, suggesting no risk of acute toxicity to algae, plants, crustaceans and insects in most freshwaters.