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Environmental fate & pathways

Biodegradation in soil

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Description of key information

Since acetone cyanhydrin hydrolyses to yield acetone and HCN, as outlined in the study for hydrolysis, this study is used to read across. Ready biodegradability of acetone is well established. This is a summary for HCN. 14C-labelled cyanide was mineralised within 30 - 60 days up to 60% by adapted soil microorganisms.

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Additional information

In a respirometric experiment radio labelled K14CN in soils sampled at two different depths in an industrial area where acetone cyanohydrin had been accidentally spilled, was mineralized up to 60% of the cyanide added to 14CO2within 30 - 60 days. Amongst the other chemical forms containing 14C, organic matter represented a small fraction (6.2-7.8%), while unidentified chemical forms counted for a relatively large fraction (25-30%).
HCN was produced only in the first few days. In this period there was an inhibition of metabolic activity and only when the soil did not produce HCN any more there was a remarkable increase in activity. The possible formation of CH3NH2 or CH4and NH3was not studied, but couldn’t be excluded, despite a predominance of oxidative pathways. The CN- is isoelectronic with N2 and can also serve as an alternative substrate for the enzyme nitrogenase soil.
The thoroughly performed experimental study is classified as acceptable and satisfies the information needs for biodegradation in soil.
These findings are in compliance with ECETOC (JACC report No. 53, Volume I, 2007): (Following quotation 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):
“The fate of cyanide in soil is the result of a complex interaction of different factors. These factors may be physical, chemical and physico-chemical (e.g. pH, volatilisation, water content, content of sulphur compounds, presence of complexing agents/equilibrium between free and complex cyanide, absorption) and biological or biochemical (e.g. presence of organisms with the capacity to metabolise cyanide, toxicity). Whether volatilisation, adsorption, complexation or biodegradation play the major role in a particular soil environment depends on the presence or absence of those factors which influence the behaviour of cyanide.”
“Cyanides can be metabolised by a wide variety of organisms, including bacteria, fungi, arthropods and plants following a number of different pathways.”