Ozonation of imidacloprid in aqueous solutions: Reaction monitoring and identification of degradation products

This paper presents the degradation of imidacloprid by ozonation. Solutions of 39.0 μg/mL imidacloprid were prepared either by dissolution of standard or by dilution of Gaucho Blé® seed loading solution and then ozonated under different conditions. The concentration of imidacloprid and oxidation products in both solutions was monitored by HPLC-UV as a function of the treatment time for a concentration of 100 g/m3 of ozone in the inlet gas. No significant difference was observed: in both cases, imidacloprid degradation was a pseudo-first order reaction with similar reaction rates (0.129-0.147 min−1), degradation by-products with the same HPLC retention times were observed and their concentrations as a function of the treatment time followed a very similar trend. The study of ozone concentration in the inlet gas (from 25 to 100 g/m3) showed that imidacloprid degradation is also a first-order reaction with respect to ozone. The ozonation by-products were then collected and identified by ESI(+)-MS. A degradation pathway of imidacloprid was finally proposed.