Cyclohexanone oxime

Endpoint summary

Additional information

Aquatic toxicity of cyclohexanone oxime was determined in acute tests for all three trophic levels algae, aquatic invertebrates (Daphnia) and fish (several species). Most sensitive were algae: In the reliable (RL 2) key study on Desmodesmus subspicatus an EC50 (72 h, growth rate) of 18.24 mg/L was determined. This is corroborated by a GLP compliant (but secondary source, RL4) study on algae performed by Environment Agency Japan (EC50 72 h, growth rate: 9.8 mg/L).

Acute toxicity towards Daphnia magna was determined to be somewhat lower, but of the same order of magnitude. The reliable key study determined an EC50 (48 h) of 22.0 mg/L (95% CI: 20 mg/L - 24 mg/L), supported by a GLP compliant study including analytical verification of test item concentration (but secondary source, RL4) performed by Environment Agency Japan. In this study an EC50 (48 h; immobilisation) of 71.7 mg/L was determined.

For fish, from the reliable (RL 2) key study on fathead minnows (Pimephales promelas) an LC50 (96 hours) of 208 mg/L (95% CI: 189-230) resulted, and the low toxicity of the submission substance towards freshwater fish is corroborated by two supporting studies on different species: Oryzias latipes was tested by Environment Agency Japan in a GLP compliant semi-static study with analytical verification of test item concentration (but secondary source, RL4). A LC50 (96 h) > 100 mg/L was determined. A further supporting 24-hours short term study on Larvae of Sea lamprey (Petromyzon marinus), Rainbow trout (Salmo gairdnerii), and Bluegill sunfish (Lepomis macrochirus) found no effects at a concentration of 5 mg/L cyclohexanone oxime (highest tested concentration).

Concluding from these acute tests, fish toxicity of cyclohexanone oxime is about one order of magnitude lower than toxicity towards aquatic invertebrates and algae. Thus, for the latter two chronic data are available and regarded to be sufficient for a safe aquatic hazard assessment:

In the algae study on Desmodesmus subspicatus outlined above besides the 72 hours EC50 also the 96 hours EC10 (growth rate) of 1.1 mg/L (95% CI: 0.20 -5.50) was determined. For Daphnia magna, a semi-static 21-days test on chronic toxicity (reproduction test according to OECD 211, reliability category 1) including analytical monitoring of test item concentration is available. A NOEC (21 d) of 4.76 mg/L resulted from this study.

Concluding from these chronic toxicity data, in line with the acute data algae are most sensitive towards cyclohexanone oxime and the 96 hours EC10 (growth rate) of 1.1 mg/L will be used for derivation of the PNEC_aqua.

For sewage treatment plants microorganisms according to "column 2" in Annex VIII of REGULATION (EC) No 1907/2006 a study on its own is not required as the submission substance has been shown to be readily biodegradable and inherently biodegradable (fulfilling specific criteria). The reliable (reliability category 2) study on inherent biodegradability will be used as key study for risk assessment (PNEC-STP-microorganisms derivation). In the available Zahn-Wellens test on inherent biodegradability performed according to EU method C.9 (equivalent to OECD 302B) an initial test item concentration of nominal 656 mg/L was applied, corresponding to 400 mg/L DOC (nominal). Actual test item concentration was slightly higher deduced from the measured DOC of 421 mg/L (value from inoculum blank subtracted). As the adaption phase was very short with degradation starting already between day 1 and 3 and 50.2% degradation reached already after 3 days (96.5% after 28 days excluding 3-h adsorption value) inoculum toxicity can safely be excluded and the initial nominal concentration of cyclohexanone oxime of 656 mg/L will be regarded as a NOEC STP-microorganisms.This is in line with REACH guidance on Information Requirements and Chemical Safety Assessment part R.10.

This is supported by a short-term test on activated sludge respiration inhibition (reliability category 3 due to short incubation period) according to ISO 8192 (draft 1984) and similar to OECD 208, where the highest tested concentration with less than 20% respiration inhibition within 30 minutes was 1199 mg/L, the EC20 (30 min) 1500 mg/L and the EC50 (30 min) 3000 mg/L.