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EC number: 200-909-4 | CAS number: 75-86-5
Toxicity to microorganisms
Administrative data
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….“
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