Sodium cyanide

Short-term toxicity to aquatic invertebrates

Description of key information

Experimental data were reviewed by U. Hommen at the Fraunhofer Institute for Molecular Biology and Applied Ecology (IME).  The report is a weight of evidence approach to an extensive body of literature on acute toxicity of aquatic organisms to cyanides, including 43 species (28 freshwater and 15 marine species) from eight major taxonomic groups.  The report uses a methodology for species sensitivity distribution consistent with EU guidance, from which an acute HC5 was derived. In addition, a recent acute toxicity assay on the effects of sodium cyanide on stickleback was reported by Van Genderen (2005). 

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

15.8 µg/L

Marine water invertebrates

Marine water invertebrates

Effect concentration:

15.8 µg/L

Additional information

The species sensitivity distribution (SSD) for acute aquatic toxicity developed by Hommen (2011) is similar to the SSD derived by the ECETOC Joint Assessment of Commodity Chemicals (2007).  The SSD by Hommen includes more recent guideline studies on acute aquatic toxicity selected after a re-assessment of the data base.  The acute HC₅ reported by Hommen for all aquatic species (15.8 ug/L) is similar to the acute toxicity HC₅ of 15 ug/L for crustacean invertebrates as estimated by ECETOC (2007). The Hommen acute SSD included the 48-h LC₅₀ value of 12.4 ug/L reported in chironomid (midge) larvae by Simon (2011). The acute HC₅ from Hommen was lower than the range of 48-h LC₅₀ values from four tests reported for cyanide in the marine copepod Acartia (191.16 - 234.65 ug/L) by Van Genderen (2006), the 96-h LC₅₀ values in yellow rock crab (44.2 - 70.9 ug/L) reported in three studies by Caldwell (2005), and the 96-h EC₅₀ of 610 ug/L in the juvenile stage of the unionid mussel Villosa iris reported by Pandolfo et al. (2012).

The acute HC₅ value of 15.8 ug/L value served as the point of departure for the derivation of the PNECaquatic for intermittent releases for both freshwater and saltwater species.

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. Support for this category approach is provided in examination of acute and chronic toxicity by oral, dermal, ocular and intraperitoneal administration of various forms of cyanide and in aquatic and terrestrial compartments of the environment, which provide consistent and comparable values when expressed as mmol/kg bw.  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.