title: Aerobic versus Anaerobic Microbial Degradation of Etofenprox in a California rice field soil.
abstract: The microbial degradation of etofenprox, an ether pyrethroid, was characterized under anaerobic (flooded) and aerobic (nonflooded) California rice field soil conditions by determination of its half-life (t1/2) and dissipation rate constant (k) and identification and quantification of degradation products at both 22 and 40 °C using LC-MS/MS. The overall anaerobic t1/2 at 22 °C ranged from 49.1 to 100 days (k=-0.0141 to -0.0069 days(-1)) compared to 27.0 days (k=-0.0257 days(-1)) at 40 °C, whereas under aerobic conditions the overall t1/2 was 27.5 days (k=-0.0252 days(-1)) at 22 °C compared to 10.1-26.5 days (k=-0.0686 to -0.0262 days(-1)) at 40 °C. The biphasic dissipation profiles were also fit to a first-order model to determine the t1/2 and k for both the fast and slow kinetic regions of the dissipation curves. Hydroxylation at the 4'-position of the phenoxy phenyl ring was the major metabolic process under anaerobic conditions for both 22 °C (maximum% yield of applied etofenprox mass=1.3±0.7%) and 40 °C (max % yield=1.2±0.8%). Oxidation of the ether moiety to the ester was the major metabolite under aerobic conditions at 22 °C (max% yield=0.5±0.1%), but at 40 °C increased amounts of the hydroxylated form were produced (max% yield=0.7±0.2%, compared to 0.3±0.1% for the ester). The hydrolytic product of the ester, 3-phenoxybenzoic acid (3-PBA), was not detected in any samples. Sterilized control soils showed little etofenprox degradation over the 56-day incubation period. Thus, the microbial population in a flooded soil was able to transform and contribute to the overall dissipation of etofenprox. The simulated summer temperature extreme (40 °C) increased the overall degradation.
authors.affiliation: Department of Environmental Toxicology, College of Agriculture and Environmental Sciences, University of California, One Shields Avenue, Davis, California 95616-8588, United States. mevasquez@ucdavis.edu
authors.forename: Martice E
authors.initials: ME
authors.lastname: Vasquez
authors.forename: Dirk M
authors.initials: DM
authors.lastname: Holstege
authors.forename: Ronald S
authors.initials: RS
authors.lastname: Tjeerdema
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D001419:Bacteria / Q000737:chemistry / Q000378:metabolism*; D001673:Biodegradation, Environmental; D002140:California; D007306:Insecticides / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D011722:Pyrethrins / Q000737:chemistry / Q000378:metabolism*; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000737:chemistry / Q000378:metabolism*
chemical_list: D007306:Insecticides; D011722:Pyrethrins; D012989:Soil Pollutants; C076840:ethofenprox