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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

The degradation of the radiolabeled test substance was investigated in a study (BASF Crop Protection, 394794, 2013) according to OECD 308 (2002) in aerobic water/sediment systems under dark conditions.  The test substance quickly redistributed from the water to the sediment phase (water phase dissipation DT50 2-3 days). In

the sediment, parent DT50 values were determined to be 121-371 days. For the whole system, the test substances degraded with a DT50 values of 76 to 86 days. The geometric mean DT50 values were 80.8, 2.4 and 211.9 days for the whole system, water and sediment phase. The mean half-lives were re-calculated to 12 °C according to equation R.16-9 in the respective REACH guidance. The resulting DT50 values were 153.3, 4.6 and 401.8 days with the corresponding degradation rates of 0.0045, 0.1492 and 0.0017 d-1 for the whole system, water and sediment phase, respectively.No

metabolites were observed in the water phase at the 10% TAR level or greater. In sediment of the aerobic aquatic study, one metabolite exceeded 10% TAR. Metabolite M440I024 reached a maximum of 10.8% TAR.

The test substance redistributed quickly from the water phase to sedimentunder anaerobic aquatic conditions as well (water phase DT50 9-13 days) (BASF Crop Protection, 394786, 2015).

Degradation of the parent occurred in total system with DT50 values of 35-45 days. Metabolite M440I001 was observed above 10% TAR in the water phase with a maximum of 14.8%. In anaerobic aquatic sediment, M440I001 reached a replicate average maximum of 30.2% TAR and M440I002 reached 12.6% TAR.

Key value for chemical safety assessment

Half-life in freshwater:
3 d
at the temperature of:
20 °C
Half-life in freshwater sediment:
121 d
at the temperature of:
20 °C

Additional information

The degradation of the radiolabeled test substance was investigated in a key study (BASF Crop Protection, 394794, 2013) according to OECD 308 (2002) unter aerobic water/sediment systems under dark conditions. Two different natural water/sediment systems were used in this study. One system was taken from a pond like side-arm of a river (Berghäuser Altrhein), the second system was taken from a small stream (Ranschgraben) surrounded by forest. The systems were treated with nicotinic acid labeled and pyranone labeled. Approximately 12 mg of the radiolabeled test substance was applied to each of the test vessels containing approximately 300 mL water and approximately 100 g dry weight equivalent sediment. This corresponds to a field application rate of about 300 g test substance per hectare. 

 

The test vessels were attached to a flow-through system for continuous aeration and incubated at a temperature of 20 ± 1 °C in the dark. Aliquots were removed for sampling at 0, 0.25, 1, 3, 7, 14, 27, 56, 78 and 100 days after treatment (DAT). An additional set of vessels was sterilized (121 °C, 30 minutes) and worked up after 101 days. Water and sediment were worked up separately. Total radioactivity in water and soil extracts was determined by liquid scintillation counting (LSC). Distribution of radioactive components was determined by HPLC with radiochemical detection. The amount of non-extractable residues was determined by combustion and LSC. Volatiles were trapped in appropriate trapping solutions and were analyzed by LSC.

 

The total radioactivity in the water decreased from 90.0%-97.6% TAR to 6.5%–9.6% TAR after 100 days. The radioactivity in the sediment increased in both systems reaching 84%-91% TAR at the end of the incubation. About 60 to 70% of the radioactivity in sediment was still extractable with acetonitrile and acetonitrile/water.

 

After 100 days, the test substance was detected in the water phase at levels of 2.6% TAR in the system Berghäuser Altrhein and 2.2% TAR in the system Ranschgraben. Several degradation products were detected, however they did not exceed 2.5% TAR. The metabolites M440I002, M440I005, M440I003, M440I006 and M440I024 were identified by comparison of retention times to those of reference items and mass spectrometry-identified metabolites in sediments.

 

The analyses of sediment extracts show that the test substance reached its highest amount after 14 or 27 days with 62.7%-68.5% TAR. After 100 days, it declined to 40.2% to 41.6% TAR and 48.2% TAR in the systems Berghäuser Altrhein and Ranschgraben, respectively. Metabolites M440I002, M440I005, M440I003 approached or slightly exceeded 5% TAR in either one of the systems. Metabolite M440I024 reached 1011% TAR for the last sampling times in system Ranschgraben. The metabolites were identified by mass spectrometry and comparison of retention times to reference items.

 

The non-extractable residues slowly increased from 24.9%25.3% TAR in system Berghäuser Altrhein and 20.3% in system Ranschgraben throughout the study.

 

The non-extractable residues of selected sediment samples were further characterized by humic substance fractionation. Approximately half of the bound radioactivity could be extracted with NaOH extraction. After fractionation of the NaOH extract into fulvic acids and humic acids, about three quarters were found in the fulvic acids and one quarter in the humic acids. The distribution of radioactivity over the different humic fractions was very similar in both systems (Berghäuser Altrhein and Ranschgraben).

 

The mineralization rate was rather low in both systems. The amount of 14CO2 never exceeded 5.3% TAR in any of the samples within 100 days.

 

The sterilized test vessels showed slightly higher test substance water concentrations (6.5%–7.4% TAR) at the end of incubation than the viable vessels (2.2%-2.6% TAR). Nearly all radioactivity recovered in the water phases or sediment extracts consisted of unchanged parent. The non-extractable residues in the sterilized test vessels were significantly lower (9.9%11.1% TAR) than those of the biological active incubations (20.3%–25.3% TAR) indicating that degradation of the test substance in sediment by incorporation into the humic substance matrix is enhanced in the presence of an active microbial population.

 

The following DT50 values for the test substance in water/sediment systems were determined. In the Berghäuser Altrhein system, the DT50 was determined to be 76, 2, and 121 days in the whole system, water, and sediment compartments respectively. In the Ranschgraben system, the DT50 was determined to be 86, 3, and 371 days in the whole system, water, and sediment compartments respectively. The degradation kinetics of metabolites M440I02, M440I03 and M440I05 were also determined.

 

Overall, the results of this study showed that the test substance dissipates readily from the water phase and then degrades at a moderate rate in the sediment when incubated in aerobic water/sediment systems under dark conditions.

 

 

In addition the anaerobic aquatic metabolism of the radiolabeled test substance was investigated in a supporting study (BASF SE, 394786, 2015) over a period of 100 days at 20°C in the dark.  The test substance was readily degraded in water/sediment systems under anaerobic conditions. The degradation DT50 value for the test substance in the total water/sediment system was 35 days for Golden Lake and 45 days for Goose River. The material balance in the both systems and labels ranged from 92.9-102.2 % TAR. There were two major metabolites above 10% TAR that were identified as M440I001 (T1) and M440I002 (T2) in both systems and labels. A minor metabolite was identified as M440I003 (T3) and reached levels above 5% TAR, but less than 10% in both systems.