Aerobic versus Anaerobic Microbial Degradation of Etofenprox in a California Rice Field Soil

• Published in: Journal of agricultural and food chemistry 2011-03, Vol.59 (6), p.2486-2492
• Main Authors: Vasquez, Martice E, Holstege, Dirk M, Tjeerdema, Ronald S
• Format: Article
• Language: English
• Subjects: aerobic conditions; Aerobiosis; agricultural soils; anaerobic conditions; Anaerobiosis; Bacteria - chemistry; Bacteria - metabolism; biodegradation; Biodegradation, Environmental; Biological and medical sciences; California; Environmental Chemistry; etofenprox; Food industries; Fundamental and applied biological sciences. Psychology; half life; hydroxylation; incubation period; Insecticides - chemistry; Insecticides - metabolism; Kinetics; oxidation; Pyrethrins - chemistry; Pyrethrins - metabolism; Soil Microbiology; Soil Pollutants - chemistry; Soil Pollutants - metabolism; summer; temperature
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf1037773

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 (t 1/2) 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 t 1/2 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 t 1/2 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 t 1/2 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.