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Abiotic processes influencing fipronil and desthiofipronil dissipation in California, USA, rice fields

2001; Wiley; Volume: 20; Issue: 5 Linguagem: Inglês

10.1002/etc.5620200506

1552-8618

Kenley K. Ngim, Donald G. Crosby,

Pharmaceutical and Antibiotic Environmental Impacts

Abstract Fipronil insecticide dissipated in California rice fields, producing half‐lives of 10.5 to 125h 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 ( t ½ = 7.97–9.42 h) and even faster in the presence of H 2 O 2 ( t ½ = 0.874–4.51 h). Fipronil was also hydrolyzed to amide in base ( t ½ = 542 h at pH 9) and volatilized slowly from water ( H = 6.60 × 10 −6 m 3 ·atm/mol) properties not explaining its rapid field water dissipation. Desthiofipronil was more stable than fipronil to direct photolysis ( t ½ = 120–149 h), was indirectly photolyzed in the presence of H 2 O 2 ( t ½ = 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.