Photolytic versus microbial degradation of clomazone in a flooded California rice field soil

• Published in: Pest management science Vol. 68; no. 8; pp. 1141 - 1147
• Main Authors: Tomco, Patrick L, Tjeerdema, Ronald S
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.08.2012; Wiley; Wiley Subscription Services, Inc
• Subjects: Agronomy. Soil science and plant productions; Bacteria - metabolism; Biological and medical sciences; California; clomazone; Floods; Fundamental and applied biological sciences. Psychology; Herbicides; Herbicides - chemistry; Herbicides - metabolism; Isoxazoles - chemistry; Isoxazoles - metabolism; Kinetics; LC/MS; Light; Mass spectrometry; Metabolites; microbial degradation; Microbiology; Molecular Structure; Oryza - chemistry; Oryza - growth & development; Oryza - metabolism; Oryza - microbiology; Oxazolidinones - chemistry; Oxazolidinones - metabolism; Parasitic plants. Weeds; photodegradation; Photolysis; Phytopathology. Animal pests. Plant and forest protection; Rice; Soil Microbiology; Soils; Time series; Water; Weeds; California; United States; North America; America; Biodegradation; Microbial activity; Monocotyledones; Isoxazole derivatives; photodegradation; Pesticides; Liquid chromatography; Rainfed lowland rice cultivation; Cereal crop; Herbicide; Paddy soil; LC/MS; Oryza sativa; Photolysis; Gramineae; microbial degradation; Angiospermae; Spermatophyta; Paddy field; Mass spectrometry; Photochemical degradation; clomazone; herbicides
• ISSN: 1526-498X; 1526-4998
• DOI: 10.1002/ps.3275

BACKGROUND: Clomazone is a popular herbicide used on California rice fields and exhibits rapid anaerobic microbial degradation (t1/2 = 7.9 days). To test the potential of direct and indirect photolytic degradation as a cofactor in the overall degradation rate, sacrificial time‐series microcosms were amended with water, non‐sterilized soil + water and sterilized soil + water. Clomazone was added to each microcosm, which was then exposed to natural and artificial sunlight over 35 days. Water and acetonitrile extracts were analyzed for clomazone and metabolites via LC/MS/MS. RESULTS: The calculated pseudo‐first‐order degradation rate constants (k) were kwater = 0–0.005 ± 0.003 day−1, ksterile = 0–0.005 ± 0.003 day−1 and knon−sterile = 0.010 ± 0.002–0.044 ± 0.007 day−1, depending on light type. The formation of ring‐open clomazone, a microbial metabolite, correlated with clomazone degradation. Trace amounts of 5‐hydroxyclomazone (m/z = 256 → 125), aromatic hydroxyclomazone (m/z = 256 → 141) and an unknown product (m/z = 268 → 125) were observed. CONCLUSIONS: The photolytic degradation rate depends on both light type and the quality of the chromophores that induce indirect photolysis. Microbial degradation was found to be sensitive to temperature fluctuations. Overall, microbes are shown to be more detrimental to the environmental fate of clomazone than photolysis. Copyright © 2012 Society of Chemical Industry