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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

The anaerobic aquatic metabolism of 14C-labelled test substance (diflufenzopyr) was studied in sediment and pond water. During the study the primary metabolite (difluoroaniline metabolite) reached a maximum concentration of 22% TAR (total applied radioactivity) by day 61 and decreased to 1% TAR by 187 DAT. The DT50 of the metabolite difluoroaniline was 27.4 days. The intermediate metabolite BH 654-5 ranged from 0.6% to 8% TAR and at 187 DAT accounted for less than 1% TAR. The present study showed that the test substance is rapidly degraded under anaerobic conditions. The DT50 of the test substance was reported to be about 7.5 days. The half-lives in water and sediment were determined to be 5.75 d at 25 °C and 7.87 d at 25 °C, respectively.

Key value for chemical safety assessment

Half-life in freshwater:
5.75 d
at the temperature of:
25 °C
Half-life in freshwater sediment:
7.87 d
at the temperature of:
25 °C

Additional information

The anaerobic aquatic metabolism of 14C-labelled test substance (diflufenzopyr) was studied in sediment and pond water in accordance with EPA Pesticide Assessment Guidelines, Subdivision N, 162-3, "Anaerobic Aquatic Metabolism" and Canadian Trade Memorandum T-l-255, DACO 8.2.3.5.5 and 8.2.3.5.6.

Under anaerobic conditions, the test substance was rapidly degraded and dispersed from the water after treatment. The radioctivity in the water layer declined with time. In the 0.4 ppm system, the radioactivity in the water phase declined steadily from an initial value of 101 % TAR (0 DAT, days after treatment) to 2% TAR after 9 months of incubation (270 days after treatment). In the sediment, the radioactivity increased after 15 days of incubation to about 26% TAR. Mineralization and other volatiles accounted for less than 0.5% TAR.

Bound residues increased from 4% TAR at 0 DAT to 83% TAR at 270 DAT. Characterization of the bound residues revealed that about 53% of these residues could be attributed to the fulvic acid and humic acid fractions.

A significant degradation of the test substance occurred under anaerobic conditions and this was accompanied by formation of BH 654-5 and BH 654-2. Metabolite difluoroaniline was formed rapidly under anaerobic conditions and reached a maximum concentration of 22% TAR by 61 days. BH 654-2 decreased to 1.1% TAR after 6 months (187 DAT).

The test substance was detected in the sediment and reached a maximum concentration after 3 months. Several unknown metabolites were detected in the sediment and none of them accounted for more than 5% TAR.

Disappearance times for test substance and the major metabolite BH 654-2 were calculated separately for each phase (water, sediment and total water and sediment). The DT50 of the parent in the total system was about 7.5 days. The DT50 of the major metabolite, BH 654-2 (difluoroaniline), in the total system was 27.4 days. The half-lives in water and sediment were determined to be 5.75 d at 25 °C and 7.87 d at 25 °C, respectively.