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A search of the available literature on cyanides revealed an extensive database of aquatic toxicity. In cases where there is a sufficiently robust database, a probabilistic approach using the whole database is preferred to derive a HC5 value, which is a species sensitivity dis tribution as used in the current EU chemical risk assessment paradigm that is based on a generic model representing the freshwater and terrestrial environment of Europe (ECB, 2003). The HC5is regarded as a ‘safe’concentration for 95% of the species (Posthuma et al, 2002). .

HCN is acutely toxic to aquatic organisms, with a 96-hour LC50 of approximately 0.025 mg/l in fish. From a guideline study of acetone cyanohydrin, the 48-hour EC50 is 0.013 mg/l in Daphnia magna.



In this analysis, the use of freshwater acute effects data is used in addition to (pooled) saltwater data for risk assessment purposes, and is supported by the empirical data on cyanides reviewed in this report (ECETOC No. 53, 2007).