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Microbial Degradation of Herbicide Pentoxaxone in Soils
Kouji SATSUMA, Osamu HAYASHI, Kiyoshi SATO, Motoo HASHIMURA and Yasuhiro KATO
J. Pestic. Sci.
25, 201-206 (2000)
The degradation of pentoxazone, 3-(4-chloro-5-cyclopentyloxy-2-fluorophenyl)-5-isopropylidene-1,3-oxazolidine-2,4-dione, was investigated in two types of paddy field soils under flooded conditions using the compounds labeled 14C at the phenyl ring. Pentoxazone was moderately metabolized to various degradation products and finally mineralized to CO2. The amount of evolved 14CO2 ranged from 8% to 23% of dosed radioactivity. When soils were sterilized, the degradation rates of pentoxazone were apparently slower than those without sterilization and no 14CO2 evolution was observed. This indicates that most of the degradation and successive mineralization have been performed by soil microorganisms. Major degradation pathways in flooded soils were proposed to include: hydrogenation of the isopropylidene moiety to 3-(4-chloro-5-cyclopentyloxy-2-fluorophenyl-5-isopropyl-1,3-oxazolidine-2,4-dione (A-0089), hydrolysis of the oxazolidine ring to N-(4-chloro-5-cyclopentyloxy-2-fluoro-phenyl)-3-methyl-2-oxobutanamide (A-0505) and its successive reduction to N-(4-chloro-5-cyclopentyloxy-2-fluo-rophenyl)-2-hydroxy-3-methylbutanamide (A-1374) and oxidative decyclopentylation to 3-(4-chloro-2-fluoro-5-hydroxyphenyl)-5-isopropylidene-1,3-oxazolidine-2,4-dione (A-1347). Additional investiga-tions demonstrated faster degradation of pentoxazone and more extensive evolution of 14CO2 under up-land condition. The major metabolites were A-1347 and further methylation product, 3-(4-chloro-2-fluoro-5-methoxyphenyl)-5-isopropylidene-1,3-oxazolidine-2,4-dione (A-1292). These results suggest that aerobes play an important role in the mineralization of pentoxazone in paddy field soils.
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