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Description of key information

DT50 = 3.9 days (irradiated samples), 10.4 days (solar summer days, Phoenix, USA) and 16.1 days (solar summer days, Athens, Greece) [M-444181-01-1]

Key value for chemical safety assessment

Half-life in soil:
3.9 d

Additional information

One study (M-444181-01-1) was performed investigating the phototransformation in soil. Phototransformation of the 14C-labelled test item was studied in one soil under laboratory aerobic conditions for 9 days at 20 °C and an initial soil moisture of 55 ± 5% of the maximum water holding capacity. The experimental study duration of 9 days was equal to 23.8 environmental days at Phoenix (Arizona, USA) and covered two phototransformation half-lives (DT75) of the test item. The study followed the OECD Draft Test Guideline for phototransformation of chemcials on soil surfaces and the US EPA OCSPP Test Guideline No. 835.2410 for photodegradation on soil and was conducted in compliance with GLP. The test item was applied with an application rate of 24.0 μg/test system. The test was performed in static systems consisting of 3 g soil dry weight. The test systems were either exposed to artificial irradiation or kept in the dark (control samples). Duplicate samples of irradiated and dark control samples were analyzed 0, 1, 2, 3, 6, 8, 9 days after application. At each sampling interval, the soil was extracted four times. Soil extracts were characterized by liquid scintillation counting (LSC) and HPLC/radiodetection analysis. The identity of the test item and its transformation products was elucidated by HPLC-MS(/MS) including accurate mass determination. The amount of volatiles was determined by LSC. Overall mean material balances were 98.5% of applied radioactivity [AR] for irradiated samples and 100.2% AR for dark control samples.

The test item was degraded in irradiated and dark control samples under laboratory aerobic conditions. The experimental DT50 values of the test item in irradiated and dark control samples were 3.9 and 12.0 days, respectively, according to single first order kinetics. Based on the experimental DT50 value of 3.9 days for irradiated samples, the half-life of the test item under environmental conditions is calculated to be e.g. 10.4 solar summer days at Phoenix (Arizona, USA) or 16.1 solar summer days at Athens (Greece).

Mineralization was observed under the conditions of the test by formation of carbon dioxide up to 3.6% AR in irradiated samples and 0.4% AR in dark control samples. One transformation product ≥10% AR, transformation product A, was detected in irradiated samples with a maximum amount of 28.6% AR and one transformation product ≥ 10% AR, transformation product B, was identified in dark control samples with a maximum amount of 15.8% AR. Both metabolites were also observed in the respective other test system as minor metabolites: The transformation product B was identified with a maximum amount of 3.7% AR in irradiated samples and the transformation product A was identified with a maximum amount of 9.1% AR in dark control samples.

Formation of non-extractable radioactivity up to a maximum of 18.1% AR (DAT-9) in irradiated samples and of 6.8% AR (DAT-8) and 6.6% AR (DAT-9) in dark control samples, respectively was observed.

The results of this study show that phototransformation in soil is likely to contribute to the degradation of 2-{2-chloro-4-mesyl-3-[(tetrahydrofuran-2-ylmethoxy)methyl]benzoyl}cyclohexane-1,3-dione under outdoor conditions.