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The principal mode of cyanide toxicity is the disruption of aerobic cellular respiration, and therefore the qualitative toxicity of cyanide among eukaryotic organisms is similar. Therefore, the aquatic toxicity of cyanides to fish, invertebrates, algae and aquatic plants has been effectively described by a species sensitivity distribution (SSD) for each of two endpoints,i.e., acute and chronic toxicity (Hommen, U., 2011. "Position paper on a refined SSD approach to derive EQS values for cyanides", Fraunhofer IME; attached). The hazardous concentration threshold for 5% of the species derived from the refined acute toxicity SSD (acute HC5) was 15.9 µg CN-/L (n=43). The hazardous concentration threshold for 5% of the species derived from the refined chronic toxicity SSD (chronic HC5) was 2.0 µg CN-/L (n=13).  The toxicity of cyanides to micro-organisms was evaluated separately; the mean EC50from activated sludge respiration inhibition tests conducted by 17 laboratories as part of an international ring test was 4.9 mg CN-/L.