Microbial degradation of herbicide pentoxazone in soils

The degradation of pentoxazone, 3-(4-chloro-5-cyclopentyloxy-2-fluorophenyl )-5-isopropylidene-1, 3-oxazolidine-2,4-dione, was investigated in two type s of paddy field soils under flooded conditions using the compounds labeled C-14 at the phenyl ring. Pentoxazone was moderately metabolized to various degradation products and finally mineralized to CO2. The amount of evolved (CO2)-C-14 ranged from 8% to 23% of dosed radioactivity. When soils were s terilized, the degradation rates of pentoxazone were apparently slower than those without sterilization and no (CO2)-C-14, evolution was observed. Thi s indicates that most of the degradation and successive mineralization have been performed by soil microorganisms. Major degradation pathways in flood ed soils were proposed to include. hydrogenation of the isopropylidene moie ty to 3-(4-chloro-5-cyclopentyloxy-2-fluorophenyl-5-isopropyl-1,3-oxazolidi ne-2,4-dione (A-0089), hydrolysis of the oxazolidine ring to N-(4-chloro-5- cyclopentyloxy-2-fluorophenyl)-3-methyl-2-oxobutanamide (A-0505) and its su ccessive reduction to N-(4-chloro-5-cyclopentyloxy-2-fluorophenyl)-2-hydrox y-3-methylbutanamide (A-1374) and oxidative decyclopentylation to 3-(4-chlo ro-2-fluoro-5-hydroxyphenyl)-5-isopropylidene-1,3-oxazolidine-2,4-dione (A- 1347). Additional investigations demonstrated taster degradation of pentoxa zone and more extensive evolution of (CO2)-C-14 under upland 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-12 92). These results suggest that aerobes play an important role in the miner alization of pentoxazone in paddy field soils.