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Environmental fate & pathways

Phototransformation in water

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Description of key information

Photolysis of 14C-labelled test substance (diflufenzopyr) (pyridine and phenyl labels) was conducted in aqueous buffer of pH 5, 7 and 9 at 22 ± 1° C under sterile conditions. The average degradation half-lives were about 16 days (pH 5), 27 days (pH 7) and 22 days (pH 9). The test substance also degraded in the dark control buffers of pH 5, 7 and 9. The average degradation half-lives were about 24 days (pH 5), 39 days (pH 7) and 41 days (pH 9). The test substance degraded to a large number of products (>14). The test substance, M1, M2, M6, M7, M23, M24, P2, P5 and P11 were major degradation /residude products. Rest of the degradation products were minor and none exceeded ~6% TAR (total applied radiation).

Key value for chemical safety assessment

Half-life in water:
27 d

Additional information

Photolysis of 14C-labelled test substance (diflufenzopyr) (pyridine and phenyl labels) was conducted in aqueous buffer of pH 5, 7 and 9 at 22 ± 1° C under sterile conditions in accrodance with US EPA Guideline, Subdivision N, 161- 2 Photolysis in Water, Commission Directive 94/37/EC amending Council Directive 91/414/EEC.

The concentrations of the pyridine labeled test substance treated buffers were 5.68 ppm (pH 5), 5.36 ppm (pH 7) and 5.33 ppm (pH 9). The concentrations of the phenyl labeled test substance treated buffers were 4.90 ppm (pH 5), 4.85 ppm (pH 7) and 4.83 ppm (pH 9). The treated buffer solutions were continuously exposed to artificial sunlight (filtered Xenon lamp). Pyridine and phenyl label treated buffer solutions were analyzed by LSC and HPLC after up to 642 hours of irradiation. The test substance degraded photolytically in pH 5, 7 and 9 buffer solutions. The average degradation half-lives were about 16 days (pH 5), 27 days (pH 7) and 22 days (pH 9). The test substance also degraded in the dark control buffers of pH 5, 7 and 9. The average degradation half-lives were about 24 days (pH 5), 39 days (pH 7) and 41 days (pH 9).

The average material balance for the entire study was very good and ranged between 94.13 - 102.52% TAR (pyridine & phenyl and irradiated & dark). The test substance degraded to a large number of products (>14). All the major radioactive residues observed were positively identified using HPLC and/or Mass Spectrometry. In the case of pyridine label more than 14 degradation products were formed. The test substance, M1, M6, M23, M24, P2 and P5 were the major radioactive residues. The rest of the degradation products were minor (<6.4% TAR). In the case of phenyl label more than 9 degradation products were formed. The test substance, M2, M7, M23, P1, P9 and P11 were the major radioactive residues. The rest of the degradation products were minor (<6% TAR). In the case of dark control (phenyl and pyridine labels) more than 9 degradation products were formed. The test substance, M1, M2, M6 and P9 were the major radioactive residues.

The quantum yield values for the test substance were 7.98 x 10E-5, 4.48 x 10E-5 and 14.8 x 10E-5 in pH 5, 7 and 9 buffers respectively.