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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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An OECD 308 Sediment Simulation study is currently underway in accordance with ECHA decision no. CCH-D-2114328256-51-01/F. Due to the physico-chemical properties of the test substance, significant difficulties were identified during analytical method development and

preliminary testing which have unavoidably delayed the study.

It was not possible to obtain radiolabelled material for use in this study. The development of suitable analytical methods to identify the test substance was complex, and necessarily preceded the preliminary work for test design, sampling regime, and extraction procedures for the definitive OECD 308 study. Preliminary testing identified the potential for volatile losses from the test system, and therefore adaptation of the test guideline and customisation of the test system was required. Further modifications to the OECD TG 308 include the selection of a spiking solvent and method to ensure distribution of the test material mainly to the sediment phase initially.

The definitive study commenced on 20thNovember 2018 and the dossier will be further updated as soon as the final result is available. Some interim data is available and presented as an attachment to the IUCLID EPS; this data is unaudited and based on a partial study, therefore interpretation of the data is approached with caution. The study is being conducted in two sediments which meet the requirements of the OECD TG 308. The first sediment system “Alte Leine” is a fine texture (52.9% clay, 15.2 % silt) sediment with an organic carbon content of 3.32%. The pH of the sediment was recorded as 6.97, and the pH of the overlying water 7.39 at the start of the acclimation phase. The second sediment system “Altwarmbüchen” is a coarse texture (1.3% clay, 2.5% silt) sediment with an organic carbon content of 0.994%. The pH of the sediment was recorded as 5.82, and the pH of the overlying water 6.79 at the start of the acclimation phase. 

In the Alte Leine sediment system, the total recovery of test item was approximately 70% (mean recovery of total test item from the water phase, sediment phase, and headspace trap, based on percentage of applied test item). The test substance dissipates rapidly from the test system (total recovery of test item approximately 17% after 3 hours and <10% after 3 days). Similar dissipation is observed in the sterile controls. In the Altwarmbüchen sediment system, the total recovery of test item was approximately 100% of the applied test item. Dissipation from the test system was slower with a total recovery of the test item approximately 34% after 3 hours, with 16% remaining after 6 days, and <10% after 22 days). The recovery of the total applied test item therefore appears to be lower, and dissipation from the system faster, in a sediment system with a higher pH. The dissipation of the test substance may be attributed to formation of the degradation products. This is consistent with the hydrolysis study, which indicates that the degradation rate increases with pH. Formation of non-extractable residues (NERs) is not anticipated, due to the physico-chemical properties of the parent substance.

 

The simulation test on ultimate degradation in surface water is waived because the substance is highly insoluble in water (and testing is not technically feasible) and furthermore exposure of the aquatic (or sediment) compartments is unlikely or negligible