Hydrogen cyanide

Short-term toxicity to fish

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

0.027 mg/L

Marine water fish

Marine water fish

Effect concentration:

0.059 mg/L

Additional information

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 species sensitivity distribution (SSD). The HC5 is regarded as a ‘safe’concentration for 95% of the species (Posthuma et al, 2002). It is 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). 

 

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).

 

The dose-response curve for lethal effects on fish is usually very steep, with concentrations without mortality (LC0) or up to 10% mortality (LC10) close to the LC50, especially for the sensitive rainbow trout.  For some species, LC50 values were only available for shorter exposure times. In principle, these 24-hour LC50 values are similar to those obtained for 96 hours. The similarity of the 24- and 96-hour LC50 values indicates that the onset of lethal effects of cyanides was very fast.

 

For a conservative analysis, the selection of tests was restricted to flow-through conditions and only the lowest LC50 per species was used resulting in a refined SSD curve. The lowest LC50 values were reported for salmonids, followed by the Atlantic silverside (Menidia menidia), bluegill sunfish (Lepomis macrochirus), perch (Perca flavescens) and cyprinids.  The lowest relevant acute LC50 values are around 25 μg CN ion/l for salmonids (rainbow trout and salmon) under worst-case conditions (low temperature or low oxygen level). Under other conditions or for other species (including other salmonids), LC50 values were generally above 50 μg CN ion/l.  The refined SSD’s estimated HC5 is 26 μg/l, corresponding well to the lowest LC50 of 27 μg/l reported for rainbow trout (Oncorhynchus mykiss).