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Toxicity to microorganisms

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Description of key information

The ECETOC Task Force identified a mean EC50 from an international ring test conducted by Strotmann and Pagga from 17 laboratories assaying growth inhibition in activated sludge; the mean EC50 was 4.9 mg CN-/l.   This value was similar to a 30-minute EC50 reported from an activated sludge respiration inhibition assay, conducted in accordance with the guideline (proposed ISO growth inhibition assay as described in Annex I to Strotmann and Pagga, 1996), of 2.3 mg CN-/l (Strotmann, 1992).
The NOEC was the lowest from range of toxicity tests to bacteria and cyanobacteria, protozoa and fungi as reviewed by the ECETOC Task Force. The lowest NOEC was 0.007 mg CN-/l.

Key value for chemical safety assessment

EC50 for microorganisms:
4.9 mg/L
EC10 or NOEC for microorganisms:
0.007 mg/L

Additional information

Review of effects of various cyanides was undertaken by the ECETOC Task Force on Cyanides.

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 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.

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