Reaction mass of ethylbenzene and m-xylene

Endpoint summary

Additional information

Acute aquatic ecotoxicity data are not available for The Reaction Mass of Ethylbenzene and m-Xylene. However, complete acute datasets are available for constituent substances o-, m-, and p-xylene isomers and ethylbenzene. Data from a chronic fish study are available for mixed xylenes. Data from chronic invertebrate and algal studies are available for m and p xylene and ethylbenzene. As these test materials are constituents of the Reaction Mass of Ethylbenzene and m-Xylene it is appropriate to read across the data.

Ethylbenzene and the xylene isomers are structurally similar substances, consisting of a benzene ring with one and two methyl functional groups attached respectively; the different xylene isomers having the two methyl functional groups attached at different locations. The presence and position of the second methyl functional group on the benzene ring is not expected to change the ecotoxicity properties of the substance significantly. The similarities in the physico-chemical properties of the components of the stream indicate that the ecotoxicity of the components is likely to be similar. All of the components are relatively soluble in water, with limited potential partition coefficients. The water solubility (Yalkowsky and He 2003) and log partition coefficient (Hansch et al. 1995) of ethylbenzene, m-, o- and p-xylene are 190.7 mg/L and 3.15, 146 mg/L and 3.2, 170.5 mg/L and 3.12, and 156 mg/L and 3.15 respectively.

The data on the xylene isomers has been taken from proprietary studies or published journal articles, for which the original sources have been reviewed. A literature search was undertaken and data were evaluated for relevance and reliability using the Klimisch scoring system (Klimisch 1997). Sufficient reliable data were identified for completion of the ecotoxicity sections of the REACH registration dossiers for the individual xylene isomers and the data has been used for the hazard assessment of the streams.

A data search on ethylbenzene identified published studies and regulatory review documents. As ethylbenzene is used as a marker substance for the streams in this category, it was considered suitable to use the review documents as reliable secondary sources for inclusion as additional evidence, without evaluating the original studies.

The European Risk Assessment Report (ECB 2007) was prepared by the German Competent Authority and interested companies following the methods set out in Commission Regulation (EC) 1488/94 and the associated Technical Guidance Document. The document has been peer-reviewed by the Scientific Committee on Health and Environmental Risks (SCHER) and therefore the report is considered to be a reliable source of information. Only studies which addressed the volatility of ethylbenzene (using flow through or closed systems with analytical measurement) were considered for inclusion in the review of the aquatic ecotoxicity data.

The Draft Screening Assessment Report (Environment Canada 2014) was prepared by the Existing Substances programs at Health Canada and Environment Canada and has undergone external written scientific peer review/consultation. Data were taken from recent literature searches (up to December 2009 for ecological sections) and review and assessment documents. When available and relevant, information presented in hazard assessments from other jurisdictions was considered. The key studies were critically evaluated, with the screening assessment presenting the most critical studies and lines of evidence pertinent to the conclusion.

According to the TLM QSAR modelling, the most sensitive species for both short term (LL50) and long term (NOELR) endpoints was Oncorhynchus mykiss, with a range of LL50 values between 4.667 - 5.921 mg/L, and a range of NOELR values between 0.894 - 1.134 mg/L. In both cases m-xylene was the test material with the lowest values.

References(not included as dossier records)

Klimisch, H.J., Andreae, M. and Tillmann, U. (1997) A systematic approach for evaluating the quality of experimental toxicological and ecotoxicological data. Regulatory toxicology and pharmacology, 25(1), pp.1-5.