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Environmental fate & pathways

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Creosote oil, acenaphthene fraction (wash oil, WO) (CAS No. 90640-84-9) is a UVCB consisting of a complex combination of polycyclic aromatic hydrocarbons of smaller molecular size. WO constituents comprise 2- and 3- ring aromatic hydrocarbon compounds. Main components are methylnaphthalenes (25% - > 50%, 1- and 2- in a ratio of about 1:2), acenaphthene (13% - 40%) and naphthalene (11% - 20%) (see Chapter 1). These main components amount to about 50% of total wash oil.

Due to the complex composition of UVCB, it is in many cases technically not practical to measure their environmental fate properties applying standard tests. To compensate for this characteristic, available data of distinct structure related substances are used as substitute/supporting substances.

As wash oil is composed of smaller size PAH, data for this class of compounds will be applied to characterise the environmental fate properties of wash oil in case information requirements are not fulfilled by wash oil specific data. Data originating from the main PAH constituents of WO (see above) are assessed to characterise properties of WO satisfactorily.

Components of wash oil are not hydrolysable, since they contain no hydrolysable groups.

Studies of the National Institute of Technology and Evaluation (NITE), Japan, on ready and inherent biodegradability using acenaphthene and naphthalene as test substances indicate that wash oil may not be biodegradable. However, in a different ready-test (OECD 301C), also published in Japan., naphthalene proved to be readily biodegradable, while 1- and 2 -methylnaphthalenes showed easy biodegradability in a MITI(II)-test, equivalent to TG OECD 302C (Yoshida et al. 1983). This is in line with biodegradation studies in soil where half-lives of key wash oil constituents were determined in the range from <2 to 35 days with only the half-life of anthracene (only 0.3% in wash oil) being somewhat higher. These aquatic and terrestrial studies are rated more reliable than the biodegradation studies of NITE. Overall, wash oil is assessed to be biodegradable in the environment.

PAH constituents of wash oil have low to moderate bioaccumulation potential with individual BCF values in fish ranging between 30 and < 2000.

Adsorption to soil is supposed to vary according to individual soil adsorption coefficients, the estimates of which range from about 1300 (naphthalene) via about 6000 (acenaphthene) to approx. 23000 (phenanthrene).