Physicochemical Transformation and Photochemical Reactions in High-Disperse Substance State: Chemical Decomposition in Aerosols and Thin Films Made from Pesticide Fipronil (Adonis)

Abstract

A chemical substance being in a high-disperse state (fine aerosol particles and very thin films) in the environment reveals specific chemical and physicochemical features which differ from the processes in a relatively coarse disperse object and, even more, in ordinary liquid and solid “test-tube” assays. The kinetics and the mechanism of the direct and sensitized photochemical destruction of pesticide compound fipronil C12H4Cl2F6N4OS have been experimented as applied to the aerosol particles ≈0.12–1.3 μm in diameter and thin films ≈0.02–0.6 μm thick on the glass plates. A non-photochemical (“dark”) reaction of fipronil molecules with the OH radicals which spontaneously proceeds in the ambient air was also observed. Quantitative estimations based on experimental results show that the fipronil pollutant, observed in the atmosphere in the form of levitated aerosols, can convert chemically in the above reaction with the OH radicals for a very short time (from several minutes for a particle 2 μm in diameter to 12–24 h for a particle of 20–30 μm). The fipronil residues presented on foliage either in the form of 1–20 μm films or as a group of deposited 2–30 μm aerosols react under sunlight by two photochemical pathways (photooxidation and photodecay). The lifetime of these residues in the ambient conditions is expected to be 11–25 days. Besides, adding a small amount of the Shirvanol 2 sensitizer to the fipronil formulation, one can increase the overall decomposition rate to 8–12 days.