Trifluoro(trifluoromethyl)oxirane

Short-term toxicity to fish

Description of key information

The short-term toxicity to fish was estimated using two separate approaches. An estimated LC50 (96 h) for freshwater fish (9.06 mg/L) was taken into account for acute fish toxicity for the derivation of the PNEC. 

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

9.06 mg/L

Additional information

Given the experimental difficulties of testing a gas, non-testing approaches were exploited to address the information requirements for this endpoint. The short-term toxicity to fish was estimated using two separate approaches, the US EPA’s ECOSAR model as well as the OECD Toolbox. A prediction of the 96 hr LC50 to fish was undertaken by ECOSAR. The test substance was found to trigger the Epoxides Mono SAR within ECOSAR. The expectation thus was that the test substance would exert a greater toxicity on account of its electrophilicity than that predicted by LogKow alone using the baseline narcosis equation (termed the neutral organics SAR within ECOSAR). The test substance was additionally profiled within the OECD Toolbox to verify its presumed mode of action. The OASIS Mode of Action and the Verhaar scheme assigned the test substance as “Reactive unspecific” and “Class 3 unspecific reactivity” respectively i.e. an excess toxicity relative to the baseline would be anticipated for the test substance. Using the estimated LogKow and measured water solubility, a LC50 was derived by ECOSAR. Other analogues identified using the OECD Toolbox containing an epoxide functionality and having a similar LogKow value were found to be reasonably predicted by ECOSAR relative to their experimental findings. The estimate was concluded to be reasonable for the purposes of characterising the endpoint.An endpoint specific grouping was also attempting using the OECD Toolbox. The Toolbox is a tool in development under the OECD QSAR workprogramme which aims to develop, justify, evaluate and document chemical categories in accordance with the REACH Technical Guidance for chemical categories. An initial grouping of substances sharing an epoxide group using the ECOSAR chemical classes served as a starting point for developing a category. A subcategorisation on the basis of protein binding alerts was then performed. Short term toxicity data in fish was then extracted and a trendline investigated. Since no significant differences were noted in the actual trendline derived for individual species vs all species, a decision was taken to maximise all the data available in order to derive as robust a correlation as possible. The TPRF provided as an attachment in IU5 describes the domain characteristics in more detail. The test substance fell within the domain described and a LC50 estimate was derived.With both approaches, the estimated 96-hr LC50 for fish was much greater than the measured water solubility for the substance. The estimated LC50 (96 h) for freshwater fish (9.06 mg/L) as determined by the OECD Toolbox was the more conservative value, hence this was used for the purposes of deriving the PNEC.