Sodium cyanide

Toxicity to terrestrial plants

Description of key information

The DuPont 1994 germination and growth studies were not able to produce reliable results under standard protocols.  The ECETOC Task Force identified a cyanide concentration in water that was tolerated by a wide range of terrestrial macrophytes based on root uptake.  When roots are exposed to cyanide in soil pore water, macrophytes appear to be very resistant to cyanide in comparison to aquatic algae. Concentrations in excess of 1 mg/l seem to be tolerated in most cases. Dormant seeds and tubers show higher resistance if exposed by air or water. 
Based on a NOEC for terrestrial plants of 1 mg/l (roots in water) and the fact that a number of soil micro-organisms are highly resistant to cyanides (EC50 for Bacillus subtilis 2,600 mg CN‾/l), the NOEC of 1 mg/l may serve as the point of departure for the derivation of a PNECsoil. 

Additional information

NOEC for terrestrial plants: 1 mg CN^-/l (roots in water).

When roots are exposed to cyanide in soil pore water, macrophytes appear to be very resistant to cyanide in comparison to aquatic algae. Concentrations in excess of 1 mg/l seem to be tolerated in most cases. Dormant seeds and tubers show higher resistance if exposed by air or water.

Based on a NOEC for terrestrial plants of 1 mg/l (roots in water) and the fact that a number of soil micro-organisms are highly resistant to cyanides (EC50 for Bacillus subtilis 2,600 mg CN‾/l), the NOEC of 1 mg/l may serve as the point of departure for the derivation of a PNECsoil.

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.