Tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate

Endpoint summary

Description of key information

Degradation and dissipation of the substance has been demonstrated to be bi-phasic within a water-sediment system. Dissipation was driven by multiple processes - partition into the water and the sediment phase, initial degradation to di-esters of the parent compound followed by further degradation and formation of carbon dioxide. The registered substance does not fulfil the persistence criterion according to REACH, Annex XIII for fresh water sediment (degradation half-life for fresh water sediment > 120 days) and would not therefore require classification as persistent (P) or very persistent (vP).

Additional information

In reported tests of both ready biodegradability and inherent biodegradability in water, the substance was considered to have relatively low biodegradability. This issue has been investigated further with additional biodegradation studies in which (prolonged) Closed Bottle tests were performed according to slightly modified OECD Test Guidelines. The tests were modified to permit measurements after 28 days as prolongation (enhanced biodegradability testing) may be used as an indicator of the non-persistence of a substance. None of the results obtained demonstrate ready biodegradability. Best results were obtained when the test substance was administered with Agnique (a non biodegradable alkylphenol alkoxylate) or in an emulsion of silicone oil and Agnique. The somewhat higher degree of biodegradation observed in tests with a lower initial test substance concentration of 1.0 mg/L indicates limited bioavailability. It is possible that the rate of biodegradation may be limited by the rate of hydrolysis of the test substance and/or the rate with which the substance dissolves. Modelling of possible biodegradation pathways indicate that aerobic degradation is likely, the first steps in this being hydrolysis to trimellitic acid and 2 -ethylhexanol, both of which have been shown to be readily biodegradable.

 

This has been investigated further in which the rate and route of degradation of the registered substance under aerobic conditions was examined in two aquatic-sediment systems, in the absence of light, at 12±2°C. Methods used were in accordance with OECD Guidelines for the Testing of Chemicals. Test No 308: Aerobic and anaerobic transformation in aquatic sediment systems OECD (2002) and C.24 (Commission Regulation (EC) No. 440/2008). Water sediment from two systems was treated with the radio-labelled substance at a single concentration in the water phase. At intervals, samples were taken and analysed. One metabolite was formed in both water-sediment systems over the course of the 100 days of the study at levels greater than 10 % of the applied radioactivity. This metabolite was identified in both systems as the di-esters of the parent substance, a tri-ester. Minor metabolites were identified as the mono-esters and trimellitic acid together with one other, unidentified, minor metabolite. The DT50 of the parent substance from the two systems was <1 day from the water phase, 39 -54 days from the sediment phase and 16 -25 days from the total system. There was evidence that mineralisation occurs, significant levels of radio-labelled carbon dioxide being measured. The mineralisation rate, based on carbon dioxide production, was 0.126 - 0.166 for both systems.

 

Degradation and dissipation of the substance has been demonstrated to be bi-phasic within a water-sediment system. Dissipation was driven by multiple processes - partition into the water and the sediment phase, initial degradation to di-esters of the parent compound followed by further degradation and formation of carbon dioxide. The registered substance does not fulfil the persistence criterion according to REACH, Annex XIII for fresh water sediment (degradation half-life for fresh water sediment > 120 days) and would not therefore require classification as persistent (P) or very persistent (vP).