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Diss Factsheets

Ecotoxicological information

Toxicity to microorganisms

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Link to relevant study record(s)

Description of key information

The study was performed in relatively short time of 15 min in buffered solution at pH 6.81. As outlined in the study for hydrolysis Frank et al. 2002 (Chapter 5.1.2) the half live is only a few minutes (t1/2 = 5.4 min at pH 6.86, t1/2 = 31 min at pH = 6.4). Therefore the EC50 should be attributed to the combined effect of acetone cyanhydrin and its degradation products acetone and free cyanide.

Key value for chemical safety assessment

EC50 for microorganisms:
21 mg/L

Additional information

In a study empoying the bioluminiscence properties of the marine bacteria Vibrio fisheri to predict the toxic effect of mixtures, the toxic effect of alpha- hydroxy-isobutyronitrile (acetone cyanhydrine) against Vibrio fisheri was examined. The EC50 based on light inhibition EC50 (light inhibition, 15 min) = 21 mg test mat./L (nominal).

Allthough the hydrolysis of acetone cyanhydrin was not monitored, free cyanide as the toxic principle should be taken into account. The study was performed in relatively short time of 15 min in buffered solution at pH 6.81. As outlined in the study for hydrolysis Frank et al. 2002 (Chapter 5.1.2) the half live is only a few minutes (t1/2 = 5.4 min at pH 6.86, t1/2 = 31 min at pH = 6.4). Therefore the EC50 should be attributed to the combined effect of acetone cyanhydrin and its degradation products acetone and free cyanide.

These finding are in aggrement 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.

Following quotations concerning toxicity of free cyanide against microorganisms 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):

“Micro-organisms show a wide range of sensitivity towards cyanide with toxicity thresholds
between 0.001 mg/l and more than 1,000 mg/l in resistant strains. In addition to this wide range, adaptive responses have been demonstrated which may increase the toxicity threshold of cyanide in a particular organism by several orders of magnitude. The metabolic and respiratory systems may be adapted in the course of a few days or weeks. A study with soil micro-organisms indicates a similar behaviour towards cyanide.
Activated sludge of wastewater treatment plants not acclimated to cyanide is sensitive to the toxicity of cyanide. Cyanide concentrations in non-adapted facilities should not exceed 0.1 mg CN-/l in order to avoid deterioration of the effluent quality. In purpose-designed systems, acclimated microbial consortia may be able to resist cyanide concentrations of 50 mg/l and more….“