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Environmental fate & pathways

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Data are available for all three xylene isomers from GLP-compliant guideline studies (Dr Noack 2015). The studies followed OECD guideline 301F (ready biodegradability: manometric respirometry test) using a mixture of sewage and soil micro-organisms. m-xylene reached 60% biodegradation after 5 days and 98% biodegradation after 28 days. o-xylene reached 60% biodegradation after 8 days and 94% biodegradation after 28 days. p-xylene reached 60% biodegradation after 7 days and 90% biodegradation after 28 days. The studies show that the xylene isomers are readily biodegradable, meeting the 10 day window criterion.

All three xylene isomers are considered readily biodegradable on the basis of the results of the GLP-compliant studies (Dr Noack 2015). On the basis of the similarity of the structure and environmental fate and behaviour of the xylene isomers, the available studies have been read across between m-, o- and p-xylene. Several additional studies are available for xylene isomers showing ready biodegradability, as well as QSAR estimates and further studies showing high levels of biodegradation. The available evidence has been used to conclude that all the xylene isomers are considered to be readily biodegradable.

Tsao et al. (1998) showed that 50% o- and p-xylene applied to soil were mineralised in 23 and 13 days, respectively, in a study following a method similar to OECD 304A. Despite differences from the guideline, the study is well described and the mass balance of applied test substance is ~90 to 94%.