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.

Fate and kinetics of carfentrazone-ethyl herbicide in California, USA, flooded rice fields.

Little is known of the environmental fate of the aryltriazolinone herbicide carfentrazone-ethyl (compound I). Rice field applications of Shark 40D commercial formulation to duplicate 5.7 m2 rings (119 g a.i./ha) and 464 m2 commercial basins (224 g a.i./ha) produced pseudo-first-order half-lives (t1/2) of 6.5 to 11.1 h in water and 37.9 to 174 h in sediment. The rapid dissipation from water was due to its hydrolysis to the chloropropionic acid (compound II), which further degraded to its propionic, cinnamic, and benzoic acids. Compound I degraded similarly in soil, but propionic and cinnamic acid levels were higher. Compound I was only weakly adsorbed, but lateral movement of compound II through soil occurred. Laboratory hydrolysis produced quantitative yields of compound II, t1/2 values of 131 h at pH 7 and 3.36 h at pH 9, and slow dissipation at pH 5 (43% at 830 h). Ultraviolet (UV) irradiation of compound I in pH 7 buffer gave dissipation rates similar to those in dark controls (t1/2 113 h vs 128 h), while compound II was comparatively stable to photolysis (t1/2 765 h) and also did not volatilize from water. Ester hydrolysis followed by off-site movement of the acid (compound II) account for the dissipation of compound I.

Elucidation of fipronil photodegradation pathways.

The phenylpyrazole insecticide fipronil (I) photolyzes to its desthio product (II) in aqueous solution. However, the necessity of an intervening oxidation to a sulfone intermediate (III) has not been resolved, and the photodegradation products of II have not been identified. Using GC-MS, HPLC-UV/vis, electrospray MS, (19)F NMR, and GC-TSD, our objective was to characterize the photodegradation pathways of I, which would clarify the role of III, identify products of II, and explain unbalanced mass accounts in previous studies. Findings showed that II is formed directly and photochemically from I, confirmed by the greater stability of III (t(1/2) 112 h), and that successive oxidations of I to III and then a sulfonate (IV) comprise a second pathway. Compound II underwent photodechlorination, substitution of chlorine by trifluoromethyl, and pyrazole ring cleavage. This work is significant to understanding the photochemistry of novel phenylpyrazole pesticides in the environment.

Optimized procedures for analyzing primary alkylamines in wines by pentafluorobenzaldehyde derivatization and GC-MS.

Biogenic primary alkylamines in wines are toxicologically significant and affect sensory properties. An optimized method for analysis in wines involving derivatization with pentafluorobenzaldehyde (PFB) to corresponding pentafluorobenzylimines, liquid-liquid extraction, and gas chromatography with mass selective detection is presented. Reaction parameters including pH, temperature, time, and derivatizing agent and amine concentration were varied in simulated wine solution (15% ethanol) to determine effect on reaction efficiency. Optimal reaction efficiency was characterized (pH 12, 24 degrees C, 30 min, and 10 mg/mL PFB), and parameters were used for the analysis of 10 biogenic alkylamines in 12 California wines. Alkylamine concentration in wines ranged from 0.048 to 91 mg/L. Amine recoveries from wines at five fortification levels (0.1-85 mg/L) were generally 81-100%.