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Environmental fate & pathways

Phototransformation in water

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Description of key information

MON 13900 is photolabile in aqueous solution. The half-life was estimated be 29.9 d of sunlight for the unsensitized experiment, and 7.85 h of sunlight for the sensitized experiment. Further, the rate constant was estimated to be 0.00193 and 0.0082/h for unsensitized and sensitized experiment, respectively. The presence of humic acid as a sensitizing agent increases the rate of photodegradation, although the photolytes formed in unsensitized and sensitized solutions are qualitatively similar. Degradation of the furan moiety was observed in all the photolytes identified from this study, while the dichloroacetyl moiety remained intact. Degradation by photolytic processes could be a significant route for the degradation of the test substance in the environment.

Key value for chemical safety assessment

Half-life in water:
29.9 d

Additional information

The photodegradation potential of MON 13900 was investif-gated in unsensitized and sensitized aqueous solutions when irradiated with artificial sunlight according to the EPA Guideline Subdivision N 161-2 in compliance with GLP. A mixture of14C and13C-test substance was formulated in acetonitrile and added to unsensitised sterile aqueous solution (pH 7) at a concentration of 48.5 mg/L test substance. The solution was irradiated with artificial sunlight (xenon arc lamp) at 25°C for 142.5 h, equivalent to 41.9 d of sunlight (assuming 12 h sunlight/day). A second solution containing 49.0 mg/L test substance was also tested (pH 7) which had been sensitized by the addition of 25 mg/L humic acid. The sensitized solution was irradiated for 122.9 h 25°C (equivalent to 36.2 d of sunlight). Comparisons were made with identical treatment controls stored in the dark at 25°C. To facilitate metabolite identification, an additional experiment was conducted at a concentration of 80 mg/L test substance exposed to the equivalent of 18.9 d of sunlight. Samples were collected daily for up to 5 d for the unsensitised and control solutions, and up to 11 d for the sensitized solutions. Volatiles (light and dark samples) and CO2(light samples only) were trapped during the study. Samples were separated into 15 fractions using a combination of ion exchange and HPLC techniques. The fractions were analyzed for radioactivity by LSC and metabolites were characterized by HPLC/RAD. Structure elucidation was done using mass spectrometry. The mean total recovered radioactivity ranged from 98.6 to 108.9% for the unsensitised and sensitized samples including controls. The test substance was extensively photolyzed to more than a dozen neutral and acidic photoproducts under unsensitized and sensitized conditions. Total accountabilities of applied radioactivity for this study ranged from 98.6 to 108.8% of applied radioactivity. No degradation was observed in the dark control solutions. The half-life was estimated be 29.9 d of sunlight for the unsensitized experiment, and 7.85 h of sunlight for the sensitized experiment. The production of14CO2totaled 1.5 and 4.9% for the unsensitized and sensitized experiments, respectively. Two major acidic photolytic products were unequivocally identified as the MON 13900 oxazolidine acid and N-(dichloroacetyl) glycine by mass spectral comparisons with authentic standards. The N-(dichloroacetyl) glycine was the most abundant photoproduct in these experiments, constituting approximately 40% of the solution-contained radioactivity after 15 d of sunlight in the sensitized photolysis experiment. In addition, structures were elucidated for five additional photoproducts based upon mass spectral data. Several additional photolyte fractions were quantified and characterized. These constituted less than 10% of the solution-contained radioactivity during the study, except for one acidic and one neutral photoproduct, each forming up to 12% of the solution-contained radioactivity in the sensitized photolysis experiment. In conclusion, the test substance is photolabile in aqueous solution. The half-life was estimated be 29.9 d of sunlight for the unsensitized experiment and 7.85 h of sunlight for the sensitized experiment. Further, the rate constant was estimated to be 0.00193 and 0.0082/h for unsensitized and sensitized experiment, respectively. The presence of humic acid as a sensitizing agent increases the rate of photodegradation, although the photolytes formed in unsensitized and sensitized solutions are qualitatively similar. Degradation of the furan moiety was observed in all the photolytes identified from this study, while the dichloroacetyl moiety remained intact. Degradation by photolytic processes could be a significant route for the degradation of the test substance in the environment.