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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

The test substance rapidly disappears from surface waters with half-lives of maximum 11.1 days whereas the maximum half-life in sediments was determined to be 21 days (under anaerobic conditions). In the presence of sediments the 14C-labeled test substance migrated to the non-extractable fraction of the sediment. The parent compound disappeared in the process of an OECD 309 study completely while several metabolites were detected. The mineralization of the test substance was determined to be low under the conditions of both studies with maximum values of 5.7% in an OECD 308 study and 25.5% in an OECD 309 study (both values based on the production of 14CO2).

Key value for chemical safety assessment

Half-life in freshwater:
11.1 d
at the temperature of:
20 °C
Half-life in freshwater sediment:
21 d
at the temperature of:
20 °C

Additional information

The biodegradability and the transformation potential of the 14C-labeled test substance was investigated in a GLP guideline study according to OECD 309 (Aerobic Mineralization in Surface Water-Simulation Biodegradation Test). The test was conducted using surface waters collected from two locations: Love Point Lake (Kent Island, Maryland, USA) and Choptank River (Denton, Maryland, USA). After a test duration of 92 days a half-life of 7.3 days was recorded for samples from the river system whereas the DT50 for samples from the lake system was 11.1 days. The degree of production of 14CO2 was 25.5% in the river system samples and 18.1% in the lake system samples after 92 days of exposure. Radio chromatography analysis of ethyl acetate extracts resulted in a similar disappearance pattern of the parent test substance from both tested surface waters. The disappearance of the parent test material was associated with the appearance of several metabolites throughout the study.

Furthermore, the distribution and transformation of the 14C-labeled test substance was studied in a GLP OECD 308 test using aerobic and anaerobic sediments obtained from the same locations as in the OECD 309 study. In both systems a radioactivity shift from the water layer to the non-extractable fraction of the sediments was demonstrated. After a test duration of 100 days 69.3 and 90.2% of the applied radioactivity was detected in the non-extractable fraction of the aerobic samples taken from both systems. In the water layer only 6.1 and 11.7% were detected. The half-lives of the test substance under aerobic conditions ranged from 3.1 to 5.8 days and from 5 to 28.9 days under anaerobic conditions, respectively. The total amount of applied radioactivity transformed into 14CO2 in aerobic test systems after 100 days of incubation was 2.8% in the aerobic Love Point Lake test systems and 5.7% in the aerobic Choptank River system. Sterile aerobic samples of the lake and river systems revealed a similar distribution. In the anaerobic samples the production of CO2 and volatile organic gases was < 1% for both lake and river systems.

Both tests demonstrate that the test substance rapidly disappears from surface waters with half-lives of maximum 11.1 days whereas the maximum half-life in sediments was determined to be 21 days (under anaerobic conditions). In the presence of sediments the radioactivity migrates to the non-extractable fraction of the sediment. The parent compound disappeared in the process of the OECD 309 study completely while several metabolites were detected.The mineralization of the test substance was determined to be low under the conditions of both studies.