Remediation of Fungicide Residues on Fresh Produce by Use of Gaseous Ozone

Ozone fumigation was explored as a means for degrading organic fungicide residues on fresh produce. Fungicides sorbed onto model abiotic glass surfaces or onto grape berries were fumigated separately in a flow-through chamber. Gaseous ozone at a constant concentration of 150 +/- 10 ppmv (mu L.L-1) selectively oxidized fungicides sorbed to model surfaces. Over 140 min, boscalid and iprodione levels did not change significantly based on a single-factor analysis of variance (ANOVA) at the 95% level of confidence (p = 0.05); however, pseudo-first-order losses resulted in observable rate constants of ozonolysis, k(ozonolysis), (min(-1)), of 0.0233 +/- 0.0029 (t (1/2) approximate to 29.7 min), 0.0168 +/- 0.0028 (t (1/2) approximate to 41.3 min), and 0.0127 +/- 0.0010 (t (1/2) approximate to 54.6 min) for fenhexamid, cyprodinil, and pyrimethanil, respectively. The relative degradation of fungicides on berries at gaseous ozone concentrations of 900 +/- 12 ppmv (mu L.L-1) over 2 h was similar to that on glass; decreases in residue concentration were observed for only fenhexamid (similar to 64%), cyprodinil (similar to 38%), and pyrimethanil (similar to 35%) with corresponding k(ozonolysis) (min(-1)) of 0.0085 +/- 0.0021 (t (1/2) approximate to 81.5 min), 0.0039 +/- 0.0008 (t (1/2) approximate to 177.7 min), and 0.0036 +/- 0.0007 (t (1/2) approximate to 192.5 min). Heterogeneous rate constants of gaseous ozone reacting with a sorbed fungicide, ko(3), (M-1.min(-1)), were calculated for both surfaces and indicate losses proceed similar to 15-fold slower on grapes. The kinetics and mechanism of fungicide removal, supported by gas chromatography- and liquid chromatography-mass spectrometry product analyses, is discussed in the context of facilitating compliance with maximum residue level (MRL) tolerances for fresh produce.