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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

On the basis of experimental data for four category members, and supporting QSAR predictions, MDI category substances are not considered readily biodegradable. The limited degradation may be a result of the low predicted water solubility of category members reducing the concentration and bioavailable fraction for degradation by micro-organisms. The category members only occur in a grease base and, in realistic use scenarios, the formulated greases are specifically designed to minimise leaching of the thickener. As such, exposure to the isolated thickener is not expected to occur and biodegradation processes in water, sediment or soil are not considered to be relevant environmental fate processes.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed
Type of water:
freshwater

Additional information

Biodegradation studies have been conducted on four substance that would fall within the category definition for the MDI category, EC 406-530-2, EC 445-760-8, EC 406-370-3 and EC 406-690-3. Studies with EC 406 -530 -2 and EC 406-690-3 were conducted according to the EC Method C5 guideline and demonstrated 8.4 % and 7.8 % biodegradation, respectively, after 28 days. The study with EC 445-760-8 was performed following the OECD 301B and EC method C4-C guidelines, and the test item demonstrated 32 % biodegradation after 28 days. The study conducted with EC 406-370-3 does not have a reported guideline, but has been previously accepted for regulatory purposes and demonstrated 48 % biodegradation during the test. Therefore, the experimental data on the substances indicate they are not readily biodegradable.

QSAR modelling using Biowin v4.10 in EPISuite v4.11 was performed for each category member where data are not available, to support read across of the experimental data. The QSAR modelling indicated that none of the category members are expected to be readily biodegradable, therefore the experimental data is deemed suitable for read across to the other category members.

A conclusion of not readily biodegradable is considered appropriate for all category members.