Abiotic processes influencing fipronil and desthiofipronil dissipation in California, USA, rice fields.
Fipronil insecticide dissipated in California rice fields, producing half-lives of 10.5 to 125 h in water and 44.5 to 533 h in soil, depending on the formulation applied and the resulting differences in water solubility. The major degradation products were desthiofipronil in water and fipronil-sulfide in soil, while the sulfone and amide were less abundant. Fipronil was photolyzed rapidly to desthiofipronil in deionized water in the laboratory (t1/2 = 7.97-9.42 h) and even faster in the presence of H2O2 (t1/2 = 0.874-4.51 h). Fipronil was also hydrolyzed to amide in base (t1/2 = 542 h at pH 9) and volatilized slowly from water (H = 6.60 x 10(-6) m3.atm/mol), properties not explaining its rapid field water dissipation. Desthiofipronil was more stable than fipronil to direct photolysis (t1/2 = 120-149 h), was indirectly photolyzed in the presence of H2O2 (t1/2 = 0.853-3.76 h), and was nonvolatile from water. The desthiofipronil observed in field water was formed photochemically from fipronil, accumulated due to slower photolysis and lack of volatility from water, but eventually dissipated.
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Department of Environmental Toxicology, University of California, One Shields Avenue, Davis, California 95616, USA.
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D002140:California; D018556:Crops, Agricultural; D006868:Hydrolysis; D007306:Insecticides / Q000737:chemistry*; D012275:Oryza; D010782:Photolysis; D011720:Pyrazoles / Q000737:chemistry*
D007306:Insecticides; D011720:Pyrazoles; C437086:desthiofipronil; C082360:fipronil