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Environmental fate & pathways

Phototransformation in soil

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Description of key information

A photolysis study with 14C-labelled test substance (diflufenzopyr) (phenyl and pyridine labels) was conducted on soil at 22 ± 1° C for 15 days for phenyl label and for about 18 days for pyridine label. The test substance degraded with a moderate rate under photolytic conditions with a half-life of about 10 days. The test substance in dark control samples degraded slowly compared to photolyzed samples and had a half-life about 20 days. The test substance degraded to a large number of products. M1 and M6 were the only degradation products found in excess of 10% TAR. The test substance itself was the largest radioactive residue at every sampling interval with the exception of the last sampling interval in the case of pyridine label in which M6 was the largest product.

Key value for chemical safety assessment

Half-life in soil:
10 d

Additional information

A photolysis study with14C-labelled test substance (diflufenzopyr) (phenyl and pyridine labels) was conducted on soil at 22 ± 1° C in accordance with US EPA Guidelines, Subdivision N, 161-3 Photodegradation on Soil Council Directive 91/414/EEC (Referring to SETAC - Europe). The study duration was about 15 days for phenyl label and about 18 days for pyridine label. The treatment rates were 1.18 ppm and 1.4 ppm for the phenyl label study #1 and study #2 respectively. The treatment rate for the pyridine label study was 1.11 ppm. The treated soil samples were continuously irradiated with simulated sunlight (filtered Xenon arc lamp) in a Atlas Suntest apparatus.

Less than 3% TAR was found as volatile radioactivity and all of it was14CO2. The material balance ranged from 90.1 - 103% TAR for the irradiated and 103-107.5% TAR for the dark control samples of phenyl label study. The material balance for pyridine label study ranged between 99.95 - 106.2% TAR and 95.9-106.6% TAR for the irradiated and dark control samples respectively.

The test substance degraded with a moderate rate under photolytic conditions with a half-life of about 10 days. In dark control samples the test substance degraded slowly compared to photolyzed samples and had a half-life about 20 days.

The test substance degraded to a large number of products. M1 and M6 were the only degradation products found in excess of 10% TAR.

The test substance itself was the largest radioactive residue at every sampling interval with the exception of the last sampling interval in the case of pyridine label in which M6 was the largest product.