2-hydroxy-2-methylpropionitrile

Short-term toxicity to aquatic invertebrates

Description of key information

As indicated in the hydrolysis study acetone cyanhydrin hydrolyses rapidly within minutes to form 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 Daphnia magna.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

0.13 mg/L

Additional information

For acute toxicity of acetone cyanhydrin against aquatic invertebrates only one study is available. The 48 hr-acute toxicity of 2-hydroxy-2-methylpropanenitril to Daphnia magna under static conditions was determined for EC₅₀ = 130 μg acetone cyanhydrin/L

(corresponding to EC50 39.8 μg CN^-/l.)  The 48 hr NOEC based on mortality was 76 mg acetone cyanhydrin/L (corresponding to 23.3 μg CN^-/l). 
Since 2-hydroxy-2-methylpropanenitril hydrolyses within a few minutes at the pH of 7.9 - 8.3 to acetone and HCN the toxic effect is attributed to the cyanide ion as the active principle. Based on the results of this study, the hydrolysis products of the test material would be classified as very toxic against Daphnia magna. The study classified as acceptable and satisfies the information needs for acute toxicity against Daphnia magna.

These finding are in with AEGL committee (US-NAC, Acetone Cyanohydrin, Interim Acute Exposure Guideline Levels (AEGLs), Interim final draft, 2005) and ECETOC (JACC report No. 53, Volume I, 2007), where the toxic effects of acetone cyanhydrin are attributed to the toxic action of the free cyanide. The principle of cyanide toxicity is similar in all organisms including micro-organisms. The cyanide ion reacts with the central metal ion of metallo-enzymes to form cyanide complexes thus rendering those enzymes non-functional.

According to ECETOC (JACC report No. 53, Volume I, 2007) there are effect records for EC50 or LC50 available for 39 taxa for free cyanide.
In a first approach the geometric mean of all tests for each species over 24 and up to 96 hours was performed. With one exception all taxa with mean values below 200 μg/l are crustaceans. Therefore crustaceans are regarded as the most sensitive taxa among the aquatic invertebrates for the endpoint acute toxicity. Almost all maximum LC50/EC50 values are lower than 200 μg CN^-/l, except for the variable EC50 values of Daphnia pulex (1 - 420 μg/l). Insects and crustaceans dominate the range between 200 and 1,000 μg/l. A  daphnid (D. magna) shows a large variability (40 - 1,900 μg/l).
Insensitive taxa with LC50/EC50 values above 1,000 μg/l are most of the molluscs, all tested oligochaeta, annelida, turbellaria and rotifera, but also isopoda (crustacea) of the genus Asellus.
Therefore, the records for the 21 crustacean species representing the most significant group were analysed in more detail. The SSD (Species sensitivity distribution) for crustaceans alone (freshwater and salt water crustaceans) resulted in an hazardous concentration for 5% of species (HC5) of 15 μg ^CN-/l with a 90% confidence interval of 5 to 31 μg CN^-/l.