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Environmental fate & pathways

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The read across approach with THPS is permitted because the hydrolysis of the cation is assumed to be independent from the anion. THPS undergoes hydrolysis at 25°C with half-life times of 133 days (pH 5), 72.2 d (pH 7) and 6.83 d (pH 9). One metabolite (THPO) is observed; its concentrations in terms of the starting concentration of the test item were 17.8% (after 29 days at pH 5), 28% (after 29 days at pH 7) and 95.9% (after 28 days at pH 9).

Laboratory experiments with photolysis by UV of aqueous solutions of the read across substance THPS (20 mg/L) showed an almost complete conversion to THPO within 2 hours both in freshwater and in synthetic seawater with maximum conversion at environmentally relevant pH.

The read across approach with THPS is permitted for the biodegradation because the anions of both substances are inorganic, and therefore only the biodegradation of the organic phosphonium cation is the key issue. For the read across substance THPS an aerobic biodegradation of >20 % after 28 days in an OECD 302B test is reported. Biodegradation simulation tests with the read across substance THPS shows half-life times of 6 days in water and 7 days in sediment.

The calculated partition coefficient log Kow value for THPC is very low (-9.8). The experimental BCF study on larvae of Artemia salina shows a maximum BCF = 93.75. The adsorption of the read across substance THPS to organic carbon in soils and sediments with 0.17 - 1.1% organic carbon was determined to be in the range Koc = 72 - 266 indicating medium to high mobility in soils and sediments.