Fipronil insecticide: Novel photochemical desulfinylation with retention of neurotoxicity

Abstract

Fipronil is an outstanding new insecticide for crop protection with good selectivity between insects and mammals. The insecticidal action involves blocking the ␥-aminobutyric acid-gated chloride channel with much greater sensitivity of this target in insects than in mammals. Fipronil contains a trif luoromethylsulfinyl moiety that is unique among the agrochemicals and therefore presumably important in its outstanding performance. We find that this substituent unexpectedly undergoes a novel and facile photoextrusion reaction on plants upon exposure to sunlight, yielding the corresponding trif luoromethylpyrazole, i.e., the desulfinyl derivative. The persistence of this photoproduct and its high neuroactivity, resulting from blocking the ␥-aminobutyric acid-gated chloride channel, suggest that it may be a significant contributor to the effectiveness of fipronil. In addition, desulfinylfipronil is not a metabolite in mammals, so the safety evaluations must take into account not only the parent compound but also this completely new environmental product.

Concentration-Dependent Degradation of Three Termiticides in Soil Under Laboratory Conditions and Their Bioavailability to Eastern Subterranean Termites (Isoptera: Rhinotermitidae)

“…The UV/VIS detector was set at ( ) 270 nm, as described by Placke and Weber (1993) and Baskaran et al (1999). For Þpronil, a methanol:water gradient (78: 22Ð72:28 over 12 min) with 1.0 ml/min ßow rate was used to separate Þpronil from the sulfone metabolite (Hainzl and Casida 1996) and the detector UV/VIS was set at 280 nm. A reverse phase C18 column (250 by 4.6 mm i.d., 5-m particle size; Luna Phenomenex) was used.…”

Environmental fate and toxicology of fipronil

“…5,[13][14][15] Fipronil possesses a greater binding affinity for the GABA-regulated chloride channels of insects than mammalian GABA receptors. 16) …”

Knockdown, Residual, and Antifeedant Activity of Pyrethroids and Home Landscape Bioinsecticides Against Japanese Beetles (Coleoptera: Scarabaeidae) on Linden Foliage

“…In some individuals, the paralysis was constant with concentrations near the LC 50 without recovery signs. The mode of action of the fipronil involves blocking the -aminobutyric acid (GABA)-gated chloride channel which is also the target for cyclodiene insecticides such as endosulfan and dieldrin (Cole et al 1993;Hainzl & Casida 1996;Durham et al 2002). Lambda-cyhalothrin and other pyrethroids are known to cause rapid paralysis in invertebrates by disrupting nerve conduction; their primary site of action are the voltage-gated sodium channels (Bloomquist & Miller 1986;Baumler & Potter 2007).…”