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Ecotoxicological information

Short-term toxicity to aquatic invertebrates

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Description of key information

The ECETOC Task Force identified and reviewed an extensive database of valid aquatic toxicity studies of fish, invertebrates and algae.  The geometric mean LC50/EC50 values for the most sensitive species of each of six groups (freshwater and saltwater representatives of fish, invertebrates and algae) were evaluated to determine a single acute LC50/EC50 for freshwater and saltwater aquatic organisms. The acute LC50/EC50 served as the point of departure for the derivation of an acute PNECaquatic value. 

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
50 µg/L
EC50/LC50 for marine water invertebrates:
50 µg/L

Additional information

The ECETOC Task Force conducted a review of short-term cyanide toxicity studies on 39 taxa of invertebrates. The lowest reliable LC50 forDaphniawas 39.8 ug CN-/l. This value was in the range of the 48-hour LC50 value at 20 degrees C forDaphnia pulexreported by reported by Cairns of 110 ug CN-/l, and is very close to the acute LC50/EC50 for all aquatic organisms of 50 ug/l derived by ECETOC.

An HC5 for free cyanide of 15 ug CN-/l was derived from an SSD representing 21 freshwater and marine crustacea; the SSD included two LC50/EC50 values of 1 ug CN-/l and 3 ug CN-/l reported inDaphnia pulexat a water temperature of 25 degrees C . The mean LC50 from two short-term studies of the marine crabCancer irroratuswas 5 ug CN-/l. The LC50/EC50 value for all other species was above 30 ug CN-/l; the results reported forCancer irroratusdo not appear to be indicative of cyanide sensitivity to marine invertebrates in general. Thus, the acute LC50/EC50 for all aquatic organisms is protective of most of the saltwater invertebrate 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 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.