The heterogeneous ozonation of pesticides adsorbed on mineral particles: Validation of the experimental setup with trifluralin

In this study, an experimental device adapted for the investigation of organic compounds with both low and high reactivity towards gaseous ozone is presented. The heterogeneous reactions were performed in a round-bottom flask connected to a rotary evaporator specially adapted to this purpose. The extract of the remaining compound on silica particles was filtered and analysed using High Pressure Liquid Chromatography with a UV detector. The kinetic was determined by following the consumption of the organic (dark, T = 26 °C, RH < 1%). The herbicide trifluralin was chosen as a test compound since its heterogeneous ozonation has already been studied in a previous work (Pflieger et al., 2009b). The obtained kinetic data was fitted by both the modified Langmuir–Hinshelwood ( k max ′  = 4.6 (±7.4) × 10−4 s−1 and KO3 = 2.4 (±4.2) × 10−16 cm3) and Eley–Rideal (kO3/ER = 1.05 (±0.06) × 10−19 cm3 molecule−1 s−1) patterns, even though this latter seems to be the most consistent model. These results confirmed that the heterogeneous reactivity of trifluralin with O3 is very slow in the atmosphere and lead to the formation of adsorbed degradation products. Moreover, our kinetic constants are in reasonable agreement (factor 3) to the one obtained in the previous study using flow tubes. Finally, our simple alternative device offers the possibility of increasing the number of heterogeneous process investigations, which constitutes an absolute necessity for issues of the environmental fate of pesticides.