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Environmental fate & pathways

Biodegradation in soil

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Evidence of cyanide biodegradation in soils was summarized by the ECETOC Task Force in Cyanides of Hydrogen, Sodium and Potassium, and Acetone Cyanohydrin (CAS No. 74 -90 -8. 143 -33 -9, 151 -50 -8 and 75 -86 -5), Volume I, JACC No. 53, September 2007).  The ECETOC Task Force reported that non-toxic concentrations of cyanide can be biodegraded by a range of organisms, including bacteria, fungi, arthropods and plants.  Biodegradation may occur through a number of different metabolic pathways, both aerobically and anaerobically. Various plants are able to remove cyanides from water and soil, and some species and tissues are efficient at doing so.   Although quantitative study of cyanide removal from aqueous systems inoculated with acclimated soil flora has been performed, sufficient data were not available to determine biodegradation half-life in soil. 

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Aronstein et al. (1994) were cited by ECETOC Task Force (Section 4.3.3, pp. 84 -85 and Section 4.3.5 p. 107 of Cyanides of Hydrogen, Sodium and Potassium, and Acetone Cyanohydrin (CAS No. 74 -90 -8. 143 -33 -9, 151 -50 -8 and 75 -86 -5), Volume I, JACC No. 53, September 2007); this study measured the removal of potassium cyanide and potassium ferrocyanide complex in aqueous systems inoculated with micro-organisms in comparison to cyanide removal rates in sterile aqueous systems, to determine biodegradation and chemical conversion. Cyanide removal rates of 42% in 13.9 days were measured for the sterile aqueous system, compared to removal rates of 59% and 66% in 14.9 days, from systems inoculated with micro-organisms isolated from cyanide-contaminated soil at a manufactured gas plant, or a methylotrophic culture of Pseudomonas ("Isolate 3"), respectively; removal rates were estimated to be approximately 33% by biodegradation and 67% by volatilisation.

The ECETOC Task Force (2007, Section 4.3.3, p. 85) also cited the work of Murrman and Koutz (1972), stating that the "cyanide salts of most cations are soluble (except AgCN) but move only a short distance through soil before being biologically converted under aerobic conditions to nitrates (by microbial degradation to NH3, then conversion to NO3_) or fixed by trace metals through complex formation. Under anaerobic conditions, cyanides denitrify to gaseous nitrogen compounds which enter the atmosphere."

The ECETOC Task Force (2007, Section 4.3.5, p. 116) cited the work of Trapp, et al. (2001a, 2001b) and Larsen et al. (2004) in a discussion regarding removal of cyanide from solutions by plant tissues of willow (Salix viminalis); the Larsen et al. study was cited by the ECETOC Task Force as showing that "(w)illow leaves removed 90% of cyanide from 1 mg/l solution in 18 hours and 82% from a 10 mg/l solution in 168 hours".