Heterogeneous oxidation of two triazole pesticides (diniconazole and tebuconazole) by OH-radicals and ozone.

Tebuconazole (Tbz) and diniconazole (Dnz) were deposited as thin film on quartz plaques. They were submitted to OH-radicals and ozone and their kinetic was measured. OH-radical oxidation was performed relative to a reference whose rate constant is well known. Terbuthylazine (Tbt) and Chlorpyriphos Ethyl (Clp) were chosen as reference for Tbz and Dnz kinetics determination, respectively. OH-radical rate constants of Tbz and Dnz were found to be: kOH+Tbz = (1.7 ±â€¯0.2) 10-13 cm3 molecule-1 s-1 and k OH+Dnz = (1.74 ±â€¯1.21) 10-12 cm3 molecule-1 s-1, respectively. Ozone heterogeneous oxidation rate constants were determined in an absolute way: kO3+Tbz = (0.5 ±â€¯0.2) 10-20 cm3 molecule-1 s-1; kO3+Dnz = (1.4 ±â€¯0.2) 10-19 cm3 molecule-1 s-1. Dnz is ten times more reactive toward OH-radicals than Tbz and 27 times more reactive than Tbz toward ozone maybe because of the presence of a double bond in Dnz. Lifetimes of Tbz and Dnz on quartz like surfaces are against OH-radicals are of 68 days and 8 days, respectively and 4 months and several years against ozone, respectively.