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Environmental fate & pathways

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The ECETOC Task Force (Cyanides of Hydrogen, Sodium and Potassium, and Acetone Cyanohydrin (CAS No. 74-90-8, 143-33 -9, 151-50-8, and 75-86-5), JACC No. 53, September 2007) evaluated the environmental fate and distribution of cyanides in the environment. Section 4.5 of that report provided this summary evaluation:

Any local emission of HCN from whatever source is distributed to the global atmosphere and enters the global HCN distribution and fate pathways. Global atmospheric movement can distribute any HCN over long distances and with a high dilution effect. Therefore it must be considered that HCN emissions from point or diffuse sources are quickly diluted and transported in air without negative effect on life forms and the environment. It is very likely that all HCN enters the global HCN input/output system which has a major sink in the global ocean systems.

There is no information in the literature of any negative effects from HCN in the atmosphere on life forms or on the environment. This also reinforces the assumption that HCN emissions can only have importance in regard to local impacts, mainly in regard to worker health considerations. Potential local impact of HCN emissions to air can be expected from direct exposure of humans to volatile HCN or from smoke released from smouldering biomass or smouldering nitrogen-containing plastics or textiles, at a short distance from the source.

Depending on the environmental conditions, the fate of cyanide in natural waters can be very complex. The major degradation process is metabolism by micro-organisms. After oxidation to cyanate, abiotic hydrolysis to ammonia and carbon dioxide may contribute to cyanide degradation After complexation of cyanides with metal salts, adsorption to sediment may occur.

The fate of cyanides in soil is the result of a complex interaction of volatilisation, absorption, complexation and biodegradation, and depends on the balance of these processes in a particular soil environment.

Cyanides can be metabolised by a wide variety of organisms, including bacteria, fungi, arthropods and plants following a number of different pathways. Degradation of cyanides in sewage treatment plants depends on the availability of adapted organisms. While standard municipal treatment plants could tolerate and remove influent concentrations in the range of 3 to 8 µg CN-/l, fully adapted sludge may be able to degrade 100 to 150 mg CN/l with a high degree of efficiency. Some plant species (e.g. basket willow) can remove cyanides from soil and/or water and may be used for remediation of cyanide-contaminated soils.