Ozone degradation of structurally distinct pesticides: A non-linear kinetic modeling approach

The study was initiated to characterize the degradation of four pesticides, which target different pest categories, by aqueous ozone and to define their degradation kinetics. Pesticide's degradation was quantified using liquid chromatographic-mass spectrometric technique and residual level served as models' dependent variable. Applied ozone dose, measured as concentration-time (Ct, min·mg/L) values, served as the independent variable. Ozone degraded the pesticides at different efficiencies, which were elucidated by data modeling. The first-order reaction kinetic model was inadequate for all tested compounds (R2, 0.1355-0.7413). Degradation kinetics of the fungicide, prochloraz, and the neonicotinoid insecticide, acetamiprid, were best described by the exponential decay model, where the rate constant, k, was 16.1 and 25.1, respectively. Notably, the offset parameter for acetamiprid kinetic model was 0.497, indicating a substantial fraction of the pesticide remaining undegraded even after prolonged exposure to ozone. Degradation of the organophosphorus insecticide, chlorpyrifos-methyl, was best fitted using an exponential-linear combination model, characterized by a dominant exponential decay with a small linear contribution. Degradation of the acaricide, fenbutatin oxide, followed Weibull decay model, indicating an initial lag before the onset of rapid degradation. Ozone Ct values for 50 % pesticides degradation (Ct50), derived from best-fit non-linear kinetic models, were 0.045, 0.601, and 2.79 min·mg/L for prochloraz, chlorpyrifos-methyl, and fenbutatin oxide, respectively. These findings suggest that (i) ozone may be effective against pesticide residue in water and food, (ii) ozone efficacy depends on the structure of the pesticide, and (iii) compound-specific kinetic models for ozone-based pesticide residue removal need to be developed.