Oxalonitrile

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

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. The report uses a methodology for species sensitivity distribution consistent with EU guidance.

Justification for type of information:

Ethanedinitrile, hydrogen cyanide (HCN), potassium cyanide and sodium cyanide can be considered as a chemical category, along with and acetone cyanohydrin (ACH, also known as 2-hydroxy-2-methylpropanenitrile), based on structural similarity, common breakdown/metabolic products in physical and biological systems, and similar physico-chemical properties. Particular attention is paid to the dissociation constant of HCN. Ethanedinitrile breaks down in aqueous solution into cyanide ion (CN-) and cyanate ion (OCN-) (Cotton and Wilkinson 1980). Ethanedinitrile due to its low log Kow (0.07) and relatively high solubility in water (2.34 g/L) needs to get dissolved in aqueous solutions in lungs to enter the body. The rate of hydrolysis of ethanedinitrile is very fast (Ajwa 2015). Also, 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 therefore result from the activity of 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 the chemical category inclusive hydrogen cyanide, sodium and potassium cyanides. 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 ethanedinitrile to a chemical category does not result in a less protective regulatory status.

Principles of method if other than guideline:

A search of the available literature on cyanides revealed an extensive database of valid aquatic toxicity studies. In cases where there is a sufficiently robust database, a probabilistic approach using the whole database is preferred to derive a species sensitivity distribution (SSD). The HC5 is regarded as a ‘safe’ concentration for 95% of the species (Posthuma et al., 2002). It is used in the current EU chemical risk assessment paradigm that is based on a generic model representing the freshwater and terrestrial environment of Europe (ECB, 2003).

GLP compliance:

not specified

Test organisms (species):

other: 13 aquatic species (eight freshwater and five marine species) from five taxonomic groups

Details on test organisms:

The species sensitivity distribution for chronic aquatic toxicity includes 13 species (eight freshwater and five marine species) from five taxonomic groups, including chordates (four fish species from three families, including Pimephales promelas [Cypronidae], Onchorhynchus mykiss [Salmonidae], Salvelinus fontinalis [Salmonidae], and Cyprinodon variegatus [Cyprinodontidae]); crustacea (four species, including Moinodaphnia macleayi, Gammarus pseudolimnaeus, Asellus communis, and Americamysis bahia); molluscs (two species, including Mytilus galloprovincialis and Chlamys asperrima); algae (two species, including Nitzschia closterium and Chlorococcales sp.); and higher plants (one species, Lemna gibba). In addition, one long-term study in insects (Chironomus riparius) reviewed but was excluded from the distribution because the highest test concentration showed no effect.

Dose descriptor:

other: chronic HC5

Effect conc.:

2 µg/L

Conc. based on:

labile/free

Remarks:

free cyanide

Basis for effect:

other: various effect endpoints

Remarks on result:

other: 90% confidence interval: 0.9 to 3.3 µg/l

Details on results:

Data from a range of multiple long-term aquatic toxicity studies for a range of freshwater and marine fish, invertebrate, algal and vascular plant species were pooled into a species sensitivity distribution (SSD). The SSD for the combination of freshwater and marine fish, invertebrate, algal and vascular plant species resulted in a HC5 of 2.0 µg/l (90% confidence interval from 0.9 to 3.3 µg/l). The HC5 value is based on free cyanide.

Conclusions:

The chronic toxicity of cyanides to aquatic organisms was determined from a species sensitivity distribution on 13 species (including eight freshwater and five marine species) from five major taxonomic groups. The chronic HC5 for both freshwater and marine species was determined to be 2.0 ug/L.

Description of key information

The chronic toxicity of cyanides to aquatic organisms was determined from a species sensitivity distribution on 13 species (including eight freshwater and five marine species) from five major taxonomic groups. The chronic HC5 for both freshwater and marine species was determined to be 2.0 ug/L.