title: Soil and glass surface photodegradation of etofenprox under simulated california rice growing conditions.
abstract: Photolysis is an important degradation process to consider when evaluating a pesticide's persistence in a rice field environment. To simulate both nonflooded and flooded California rice field conditions, the photolytic degradation of etofenprox, an ether pyrethroid, was characterized on an air-dried rice soil and a flooded rice soil surface by determination of its half-life (t(1/2)), dissipation rate constant (k) and identification and quantitation of degradation products using LC/MS/MS. Photodegradation was also characterized on a glass surface alone to rule out confounding soil factors. Measured photolytic dissipation rates were used as input parameters into a multimedia environmental fate model to predict etofenprox persistence in a rice field environment. Photolytic degradation proceeded at a faster rate (0.23/day, t(1/2) = 3.0 days) on the flooded soil surface compared to the air-dried surface (0.039/day, t(1/2) = 18 days). Etofenprox degradation occurred relatively quickly on the glass surface (3.1/day, t(1/2) = 0.23 days or 5.5 h) compared to both flooded and air-dried soil layers. Oxidation of the ether moiety to the ester was the major product on all surfaces (max % yield range = 0.2 ± 0.1% to 9.3 ± 2.3%). The hydroxylation product at the 4' position of the phenoxy phenyl ring was detected on all surfaces (max % yield range = 0.2 ± 0.1% to 4.1 ± 1.0%). The air-dried soil surface did not contain detectable residues of the ester cleavage product, whereas it was quantitated on the flooded soil (max % yield = 0.6 ± 0.3%) and glass surface (max % yield = 3.6 ± 0.6%). Dissipation of the insecticide in dark controls was significantly different (p < 0.05) compared to the light-exposed surfaces indicating that degradation was by photolysis. Laboratory studies and fate model predictions suggest photolysis will be an important process in the overall degradation of etofenprox in a rice field environment.
authors.affiliation: Department of Environmental Toxicology, University of California, Davis, CA 95616-8588, USA. mevasquez@ucdavis.edu
authors.forename: Martice
authors.initials: M
authors.lastname: Vasquez
authors.forename: Thomas
authors.initials: T
authors.lastname: Cahill
authors.forename: Ronald
authors.initials: R
authors.lastname: Tjeerdema
mesh_terms: D002140:California; D005898:Glass / Q000032:analysis; D007700:Kinetics; D012275:Oryza / Q000187:drug effects / Q000254:growth & development*; D010575:Pesticides / Q000737:chemistry*; D010782:Photolysis; D011722:Pyrethrins / Q000737:chemistry*; D012987:Soil / Q000032:analysis*; D014867:Water / Q000032:analysis
chemical_list: D010575:Pesticides; D011722:Pyrethrins; D012987:Soil; D014867:Water; C076840:ethofenprox