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Environmental fate & pathways

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It was not considered necessary to conduct biodegradation simulation tests in water, soil or sediment on the registered substance owing to the low water solubility of the substance (3 mg/l at 25°C), further, the substance is a UVCB and it is therefore not feasible to apply standard test methods for simulation testing to the substance. During testing for ready biodegradation of the substance it was found that the substance had to be spread on a glass plate and inserted into the inoculated mineral medium before the study could commence. There is not expected to be direct or indirect exposure to soil during the identified uses of the substance.

The results of the ready biodegradation study on Thermal cracking oil from blends of rubber, fuel oils and paraffin waxes, steam-stripped show that the substance cannot be considered as readily biodegradable and is therefore expected to persist in the environment. The substance demonstrated 6% biodegradation (average of two replicates) over 28 -days. The lack of biodegradation observed with the test substance is predicted to be due to the low water solubility of the substance (3mg/l at 25°C). The low biodegradation is not due to the inherent toxicity of the substance as it was found not to be inhibitory to the sewage sludge microorganisms, based on a toxicity control degradation of 33% by day 12. In addition, QSAR calculations on the components of the substance demonstrate that they are unlikely to be toxic to STP organisms. Some components, which make up a significant proportion of the substance, are expected to be biodegradable e.g. limonene, aromatic hydrocarbons. As such it is considered that it is the low water solubility of the UVCB substance, along with the inherent difficulties of applying standard test methods to a UVCB substance, which causes the observed low degree of biodegradation. This conclusion is supported by information available in ECHA's Endpoint Specific Guidance, Chapter R.7B, which states that “a large proportion of UVCB petroleum substances will remain in the undissolved phase and will therefore not be fully available to the degrading organisms, as such the recorded biodegradation will be an underestimate of the true potential of the substance to biodegrade in the environment”)