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Environmental fate & pathways

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Hydrogen cyanide and soluble cyanide salts are not bioaccumulative in aquatic or terrestrial environments. The octanol-water partitioning coefficient (Kow) for hydrogen cyanide is not indicative of the potential for bioaccumulation, i.e., the log Kow of -0.25 for hydrogen cyanide is substantially less than the threshold log Kow of 3 or more that is indicative of the potential for bioaccumulation (ECHA, May 2008, Guidance on information requirements and chemical safety assessment, Chapter R.7, Endpoint-specific guidance, Section R. Callahan et al. (United States Environmental Protection Agency, 1979) state "there is little potential for bioaccumulation of hydrogen cyanides." A predicted BCF = 3.162 L/kg wet weight (log BCF = 0.500) was obtained from BCFBAF version 3.00, a QSAR model within U.S. EPA's EPISuite program; the BCF predictions of this model may be applied, for screening purposes, to organisms in aquatic and terrestrial environments. This predicted BCF is substantially below the threshold BCF values of >2000 L/kg and >5000 L/kg for classification as PBT and vPvB, respectively (ECHA, May 2008. Guidance on information requirements and chemical safety assessment, Chapter R.11, PBT Assessment, Table R.11 -1).

Potassium cyanide and sodium cyanide can be considered as a chemical category, along with hydrogen cyanide (HCN) and acetone cyanohydrin (ACH, also known as 2-hydroxy-2-methylpropanenitrile), based on structural similarity, similar physico-chemical properties and common breakdown/metabolic products in physical and biological systems. Particular attention is paid to the dissociation constant of HCN. In the vast majority of environmental and physiologic conditions, the cyanide salts will dissolve in water to form hydrogen cyanide. The physico-chemical hazards and toxicity result from the activity of this common proximal toxicant, HCN.An ECETOC Task Force, in the 2007 ECETOC Joint Assessment of Commodity Chemicals ( 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)” supports the development of this chemical category. Hydrogen cyanide (Index No.006-006-00-X) and salts of hydrogen cyanides (Index No.006-007-00-5) are both listed in Annex VI,Table 3.1 of Regulation (EC) No. 1272/2008, entry 006-007-00-5, and are restricted in comparable ways taking into account physical characteristics. Thus, the assignment of potassium cyanide and sodium cyanide to a chemical category does not result in a less protective regulatory status.