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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 (CN- anion) in physical and biological systems. Particular attention is paid to the dissociation constant of HCN, 9.36 at 20 o C; in normal environmental and physiological conditions, the CN- anion will be hydrated to HCN, regardless of its origin in NaCN, KCN, ACH or HCN.

Hydrogen cyanide will distribute in the body to blood (erythrocytes), muscles and other organs. Metabolism occurs in muscles and organs mainly via rhodanese, forming thiocyanate which is excreted in the urine. Saturation of the enzyme results in build-up of HCN and acute toxicity. Chronic toxicity involves competition by thiocyanate with iodine transfer into the thyroid, with the consequence of increased secretion of thyroid stimulating hormone (TSH) and development of goitre.

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 a chemical category including hydrogen cyanide, potassium cyanide, sodium cyanide and acetone cyanohydrin. 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.