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The substance is considered to be very persistent in the environment

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Based on biodegradation screening and simulation tests, the substance is considered to be persistent in the environment. The substance to register was found to be poorly biodegradable in a Closed bottle test according to OECD guideline 301D (Huntington 1996). In addition, several biodegradation data are available for the main component Triphenyl thiophosphate (structure A). 17.8 and 19.3% mineralization (CO2 evolution) was observed in 28 days in a modified Sturm test (OECD 301B). Further investigations during experimental phase using radiolabelled test item showed that only 51.5% and 60.8% of the radioactivity consisted of the test item, whereas the remaining radioactivity consisted of its degradation products. Thus, the test item is not completely biodegraded over a 28-day period under the test conditions but up to 19% is mineralized and additionally up to 48.5% of the test item is transformed into its transformation and degradation products. Phenol can be identified from the chromatogram of the degradation products. This is supported by the results of the hydrolysis study, which showed that different transformation products of the test substances are generated in parallel once hydrolysis has started. The results indicate that the test item cannot be classified readily biodegradable but well primarily degradable under conditions of the test. An inherent biodegradability test with Structure A according to OECD 302C confirmed this result. The test material showed up to 59.5 and 66.8 % biodegradation after 28 days. These results indicate that the test item can be degraded if sufficient degrading microorganisms are available; however, this is not necessarily be the case in surface water. A study investigating the biodegradation of O,O,O-triphenyl phosphorothioate under environmental conditions according to GLP and OECD guideline 309 using radiolabelled test material showed only very low mineralization of 3.1 – 3.7%. No organic volatiles were detected (≤ 0.1 % AR). The amount of parent after 61 days was in the range of 80.2 % to 90.5 % AR. The DT50 value is determined to be > 61 days.  Reason for the low degradation are assumed to be low microorganism concentrations and adsorption of the components to DOC which might lower bioavailability of the substances to microorganisms.