Ethylene oxide

Long-term toxicity to fish

Description of key information

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Additional information

Considering the physical and chemical properties of ethylene oxide a prolonged exposure of aquatic organisms to concentrations causing adverse effects in fish is not expected. Ethylene oxide is readily biodegradable and hence a major fraction of the substance is eliminated in sewage treatment processes. Ethylene oxide reaching surface waters will remain to a major part in this compartment. This was demonstrated using a Mackay Level I distribution calculation, where more than 90 % of ethylene oxide is expected to remain in the water compartment. However ethylene oxide is expected to undergo rapid degradation by microorganisms in surface waters and, due to the very high water solubility and the low log Koc of 0.51, adsorption to suspended matter and subsequent transfer to sediment appears to be negligible. This consideration is in accordance to the results of Mackay Level I calculations in which the mass amount in sediment was calculated to be 0 % and 0.08 %, respectively. Ethylene oxide is an epoxide and therefore generally susceptible to hydrolysis. In a hydrolysis study performed by Conway and co-workers (1983) the half-life of ethylene oxide was 12.2 days in sterilized distilled water and 14.9 days in natural river water samples. Ethylene oxide hydrolyses to 1,2-ethanediol which is of very low toxicity and also readily biodegradable (see IUCLID Ch. 5.2.1). Additionally, ethylene oxide has a high vapor pressure (145600 Pa) and a Henry Law Constant of 12.2 Pa*m3/mol. Further, Conway and co-workers (1983) studied the volatilization of ethylene oxide from water and determined a half-life in thoroughly agitated water of approximately 45 minutes with wind flow and about 60 minutes without wind. The combination of degradation, hydrolysis and volatilization of ethylene oxide indicates that concentrations present in surface waters for an elevated time are expected to be well below levels that may cause long-term adverse effects in aquatic organisms. In accordance with section 3 paragraph 3.2(b) of Annex XI of the REACh regulation 1907/2006 amended by Commission regulation (EC) No 134/2009 testing may be omitted based on the exposure scenarios developed in the Chemical Safety Report (CSR). In case of EO in chapter 9 of the CSR a qualitative exposure assessment is provided that demonstrates that releases into the environment are considered to be negligible due to the strictly controlled conditions under which EO is manufactured and handled. Based on the presented fate data of ethylene oxide and for reasons of animal welfare it is deemed justified not to provide a long-term toxicity fish study.