Reaction kinetics and mechanisms of degradation of organosilicon fungicide flusilazole

MERCADO, D. FABIO; LARISA L.B. BRACCO; MONICA CRISTINA GONZALEZ; PAULA CAREGNATO

Villa Carlos Paz, Cordoba

Congreso; XIII Encuentro Latino-Americano de Fotoquímica y Fotobiología (XIII ELAFOT); 2017

Universidad Nacional de Cordoba

Flusilazole is a triazole family fungicide. Because of its broad-spectrum of application, exhibits curative and preventive properties and is recommended for use in agriculture, horticulture and viticulture.Hazard classification for flusilazole is class III, ´slightly hazardous´ [1]. However, it is important to take into account, that indiscriminate use of pesticides, could lead accumulation in plants, foods, water reservoirs and food chain. Besides, some of them are resistant to the action of sunlight, temperature, water or microorganisms; resulting in high levels residues in plant tissue and environmental samples.Sulphate and hydroxyl radicals are strong oxidants used in advanced oxidation processes (AOPs), like UV/ S2O82?, Fenton and the photo-assisted Fenton reaction (?photo-Fenton?). Those processes have attracted interest for the degradation of organic compounds in wastewater, including pesticides [2] [3].Despite flusilazole is a widely used fungicide, documented data on their degradation mechanism and intermediate metabolites is lacking. In the present work we investigated the kinetics and mechanism of the degradation of flusilazole initialed by HO? and SO4??. These radicals were generated by laser flash photolysis (λexc.=266nm) of H2O2 and Na2S2O8, respectively. Also, continuous-irradiation experiments were performed by ?photo-Fenton? reaction of the fungicide with solar simulator and the nature of the primary degradation products formed were investigated by GC-MS analysis.A possible degradation mechanism of the fungicide was proposed. To help identify the nature of the observed transients, time-dependent density functional theory (TD-DFT) calculations were employed. By laser flash photolysis of S2O82? with flusilazole, two absorbing intermediates were identified: the first transient absorbs at wavelengths of 300nm, and the second one has two maxima at 360 nm and 640 nm.Using TD-DFT, intermediates were identified as a carbon centered radical (a structure) and siloxyl radicals Si?O? (b structure).In the continuous photolysis experiments, performed by photo-Fenton reaction of the fungicide, the main degradation product was silicic acid, diethyl bis(trimethylsilyl) ester. Silicon in the structure of flusilazole is fundamental for the generation of the intermediates proposed, which have in their structure Si-O-Si and Si-C bonds.