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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

There are no data available on water or sediment simulation tests.

Key value for chemical safety assessment

Additional information

Information concerning effects on biodegradation of the test substance insurface water (simulation testing) as well as the identification of degradation products are not available. According to column 2 of Annex IX of Regulation (EC) No. 1907/2006, a simulation test is needed if the chemical safety assessment indicates the need to investigate further the degradation of the substance and its degradation products. 

Although the substance was not readily biodegradable in an OECD TG 310 study (CO2 headspace test) and hydrolysis is not considered to be a relevant pathway of degradation, the substance is not expected to be persistent based on QSAR modelling of physicochemical and environmental fate data performed for all relevant constituents (>0.1%). 

REACh regulation, Annex XIII defines criteria for the identification of persistent substances. In section I of this Annex,cut-off values for degradation half-life in water (>40d fresh water) and soil (>120d) are defined to identify persistent substances. As a preamble to this section, it is stated, that a weight-of-evidence determination using expert judgement shall be applied, by comparing all relevant and available information as set out in Reach Annex XIII, section 3.1.1. and 3.2.1., respectively. Besides simulation testing also “other information” can be used, provided that its suitability and reliability can be reasonably demonstrated. 

For Oxooil LS9, other than biotic degradation pathways are more relevant, e.g. photodegradation in the air. Oxooil LS9 is highly volatile from water and soil. In the environment, the atmosphere is therefore the main target compartment. In the atmosphere, Oxooil LS9 undergoes rapid degradation by oxidation with OH-radicals.

For the relevance of atmospheric degradation for the entire environment (and the P-criterion), not only the rate of degradation in the atmosphere has to be considered: Also transport between compartments plays a major role. Volatilisation half-lives of all relevant constituents of Oxooil LS9 from a model river and lake were estimated to be1.1 hours for river and 101.5 hours (4.2 days) for lake. 

The half-life of the volatilization out of a lake of 4.2 days results, after 10 and 28 days, respectively, in a residual content of the substance of 19.2%, and 1% (elimination 80.8% and 99%, respectively).

A steady state, non-equilibrium fugacity model (Mackay level III model, included in EpiSuite v. 4.11) demonstrated that all relevant components will predominantly partition to water or volatilise into air to significant amounts (>90% partition to air and water; only <10% partition to sediment and soil)whenusing actual release rates Persistence times ranging from 80.9 to 273 hours (3.4 – 11.3 days)were calculated, which is significantly lower than the 960 hours of the persistence criterion in freshwater (40 days). 

Overall, these results indicate fast photodegradation of the substance. Consideration of these degradation processes supports the assessment that the substance will degrade relatively rapidly in the environment and does not persist. Therefore, further testing on biodegradation (simulation testing on ultimate degradation in surface water (Annex IX, Section as well as the identification ofdegradation products (Annex IX, Section 9.2.3.)  is not considered to be necessary, since other degradation pathways (mainly photodegradation) contribute to a more relevant degree.  

The risk for the compartment surface water and sediment based on available data is acceptable. Hence, according to column 2 of Annex IX, section 9.2, currently further degradation testing of the substance is not indicated.