Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

The uvcb substance is not readily biodegradable and is expected to disappear quickly in natural environment by adsorption to sediments and abiotic/biotic transformation processes with almost no significant mineralization.

Additional information

Data on ready biodegradability tests dertermined with QSAR and on a surface water degradation simulation study with radiolabeled test material are available.

Both test types show that the uvcb substance and its major constituents are not readily biodegradable and have a potential for primary degradation.

However, in the simulation study the mineralization was below 1% and in the modelled data were between 24 and 31% for the main isomer groups. Formation of degradation products was observed in the surface water test but could not be identified or quantified. The modelled data indicate > 100 degradation products. This difference can be explained with the different test conditions. Ready biodegradability tests according to 301C are performed at 22°C and with high amount of sludge inoculum which improves the biodegradation capacities.

The simulation tests in surface water is on the one hand closer to environmental conditions as the test system is natural water but temperature and concentration of suspended solids is low and represent worst case conditions for biodegradation. Furthermore, the constituents of the uvcb substance have high sorption capacities, and decrease of overall radioactivity in the surface water test can be explained with sorption to test vessels.

Degradation pathways of constituents/different degradation products as well as adsorption processes are interfering during the test. Therefore, interpretation of the degradation pathways from the surface water test is very complex or even impossible if the parent substance is an uvcb substance.A lot of further peaks in the water phase which could be transformation products were observed but it was not possible to dissolve them chromatographically with highly sophisticated methods, or even to assign them to one of the isomer groups of the test item as possible parent substances. No analysis of the adsorbed part of the uvcb substance and degradation products was possible.

The same technical difficulties as in the surface water simulation test, to analyse and recover the substances including transformation products, are expected in further degradation studies. The constituents of the uvcb substance are highly adsorptive and as for the study according to OECD 309 it was technically not feasible to achieve the recovery of the test item and the radioactivity completely due to adsorption to test equipment. In studies with additionally more substrate for adsorption like sediment simulation tests according to OECD 308 and soil simulation tests according to OECD 307 even more problems for recovery are expected. Despite the technical limitations with such adsorptive substances in further simulation degradation studies, the interpretation of the results concerning degradation pathways is not possible for uvcb substances like the substance tested. The available data show both the biodegradation potential based on the modelled data and biodegradation under worst case environmental conditions based on the experimental data on degradation in surface water. Any further simulation biodegradation test would not reveal any different findings.