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Sediment toxicity

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The behavior of sodium cyanide and potassium cyanide are expected to be similar to hydrogen cyanide, which is not strongly partitioned into the sediments or suspended adsorbents, primarily due to its high solubility in water (Callahan et al, 1979).  Cyanides are relatively mobile in the soil environment (Alesii and Fuller, 1976), indicating that adsorption to sediment is unlikely to be significant in most aquatic environments (ECETOC JACC No. 53 Report, Vol. I., Section 4.3.2, p. 82).  Therefore, sediment toxicity was evaluated on the basis of a chronic sediment-water chironomid toxicity test using spiked water.  No significant effects were observed in the study, and therefore the NOEC was determined to be ≥ 1.65 ug/L (based on geomean measured concentration of the highest test concentration).  At one significant figure, the NOEC of ≥ 1.65 ug/L is equivalent to the chronic HC5 of 2 ug/L from the species sensitivity distribution for aquatic organisms (freshwater and marine).  Therefore, the PNEC values for freshwater and marine sediments were each derived based on long-term toxicity data for aquatic organisms (chronic HC5 = 2 ug/L), using the equilibrium partitioning method (EPM). 

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Additional information

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 cyanide (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.