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Ecotoxicological information

Short-term toxicity to fish

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Description of key information

As indicated in the hydrolysis study acetone cyanhydrin hydrolyses rapidly within minutes to acetone and cyanide. The study was performed over 24 hours. Therefore the toxic principle is the cyanide ion. The hydrolysis products of acetone cyanhydrin were very toxic against fish.

Key value for chemical safety assessment

Additional information

(Following quotations taken with kind permission from ECETOC JACC report no. 53; Cyanides of Hydrogen, Sodium and Potassium, and Acetone Cyanohydrin (CAS No. 74-90-8, 143-33-9, 151-50-8 and 75-86-5)

Acute toxicity of cyanides to aquatic organisms… has been studied extensively. Acute toxicity to fish as 96-hour LC50 values ranged from 27 to 169 μg/l.
The lowest value was obtained for rainbow trout (O. mykiss) under flow-through conditions. Saltwater species were generally less sensitive than freshwater species (≈
factor 2).
Reliable 96-hour LC50 values for cyanides are available for 19 fish species ….
Most tests have been conducted with fathead minnow (Pimephales promelas), brook trout (Salvelinus fontinalis), bluegill sunfish (Lepomis macrochirus), rainbow trout (Oncorhynchus mykiss, formerly named Salmo gairdneri) and perch (Perca flavescens). Other taxa have only

been tested once or within one study at different temperatures. For species tested several times, the minimum and maximum LC50 values can vary by up to one order of magnitude, which is explained by differences in test conditions and life stages tested. For cold water fish, sensitivity is usually higher at lower temperature and eggs and fry are usually less sensitive

then juveniles.
For a conservative analysis, the selection of tests was restricted to flow-through conditions and only the lowest LC50 per species was used (Table 27), resulting in a refined SSD curve (Species sensitivity distribution 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 SSD provides a HC5
 of 26 μg/l, which predicts that for 95% of species the LC50 is higher than this value, corresponds to the lowest LC50 of 27 μg/l reported for rainbow trout (Oncorhynchus mykiss). This lowest reported LC50 was derived from a test with a water temperature at 6°C.
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. These data indicate that a factor of 5 applied to an LC50 should predict a safe concentration for survival.
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