Residues, dissipation, and dietary risk assessment of oxadixyl and cymoxanil in cucumber

Oxadixyl and cymoxanil are widely used for controlling downy mildew in cucumber; however, there are few systematic studies on monitoring residue levels of these two pesticides in cucumber under greenhouse and open field conditions. In this study, a simplified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method was applied to analyze target compounds in cucumber. The average recoveries of oxadixyl and cymoxanil in cucumber ranged from 96% to 102%, with relative standard deviations (RSDs) of 1.8%–4.0%. The limits of quantification (LOQs) for two pesticides were both 0.01 mg/kg. The dissipation of oxadixyl was in accordance with a first-order kinetics equation, with half-lives ranging from 1.8 to 3.1 days. At the pre-harvest interval (PHI) of 3 or 5 days, the residue levels of oxadixyl in cucumber under open field conditions were higher than those under greenhouse conditions. Compared to oxadixyl, the cymoxanil degraded quickly, and its residues were below LOQ on the 3rd or 5th day after the last application. The terminal residues of oxadixyl and cymoxanil in the cucumber were both lower than the maximum residue limits (MRLs) in China. The risk quotient (RQ) used for dietary risk assessment was 1.8%–3.5% and 0.26%–0.51% for oxadixyl and cymoxanil, respectively. The results showed that the risks of these two pesticides used on cucumber at the experimental dosages are comparably acceptable for Chinese consumers of different gender and age groups. This study provides a reference data to use oxadixyl and cymoxanil scientifically and rationally.