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Environmental fate & pathways

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On the basis of the similarity of the structure and environmental fate and behaviour of the xylene isomers, data from all the xylene isomers have been read across and used to determine their likely environmental fate.

GLP-compliant, guideline studies are available for xylene isomers showing that they are ready biodegradable and these are supported by QSAR estimates and additional studies showing high levels of biodegradation. 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. Atkinson (1985) indicates that the xylene isomers would degrade by indirect photolysis in air, with a half-life of approximately 1 day. The xylene isomers are not expected to undergo hydrolysis due to the lack of hydrolysable functional groups.

Xylenes are expected to have low potential for bioaccumulation based on a measured BCF of 29 in fish for mixed xylene isomers. The measured log Koc value of 2.73 for o-xylene indicates that xylene isomers are expected to have moderate adsorption to suspended solids and sediment in water.

The available data indicate that xylene isomers are readily biodegradable. Therefore, based on the screening criteria for persistence in the PBT assessment, the individual xylene isomers are not considered to be persistent (P) or very persistent (vP). The xylene isomers have a log Kow in the range of 3.12 to 3.2 and the measured BCF for mixed xylenes is 25.9 L/kg. Therefore, on the basis of the screening and definitive criteria, the xylene isomers are not considered bioaccumulative (B) or very bioaccumulative (vB).