Purified Chlorine Dioxide as an Alternative to Chlorine Disinfection to Minimize Chlorate Formation During Postharvest Produce Washing

Compared to chlorine, purified chlorine dioxide reducesthe concentrations of chlorate and halogenated organic byproductsin produce under simulated postharvest washing conditions. The washwater used to wash produce within postharvestwashing facilitiesfrequently contains high chlorine concentrations to prevent pathogencross-contamination. To address concerns regarding the formation anduptake of chlorate (ClO3 (-)) into produce,this study evaluated whether switching to chlorine dioxide (ClO2) could reduce chlorate concentrations within the produce.Because ClO2 exhibits lower disinfectant demand than chlorine,substantially lower concentrations can be applied. However, ClO3 (-) can form through several pathways, particularlyby reactions between ClO2 and the chlorine used to generateClO(2) via reaction with chlorite (ClO2 (-)) or chlorine that forms when ClO2 reacts with produce.This study demonstrates that purging ClO2 from the chlorineand ClO2 (-) mixture used for its generationthrough a trap containing ClO2 (-) can scavengechlorine, substantially reducing ClO3 (-) concentrations in ClO2 stock solutions. Addition of lowconcentrations of ammonia to the produce washwater further reducedClO(3) (-) formation by binding the chlorineproduced by ClO2 reactions with produce as inactive chloramineswithout scavenging ClO2. While chlorate concentrationsin lettuce, kale, and broccoli exceeded regulatory guidelines duringtreatment with chlorine, ClO3 (-) concentrationswere below regulatory guidelines for each of these vegetables whentreated with ClO2 together with these two purificationmeasures. Switching to purified ClO2 also reduced the concentrationsof lipid-bound oleic acid chlorohydrins and protein-bound chlorotyrosines,which are exemplars of halogenated byproducts formed from disinfectantreactions with biomolecules within produce.

Automated summary

Compared to chlorine, purified chlorine dioxide can reduce the concentrations of chlorate and halogenated organic byproducts in produce under postharvest washing conditions. Chlorine dioxide exhibits lower disinfectant demand than chlorine, allowing for lower concentrations to be applied. This study demonstrates that purging ClO2 from the chlorine and ClO2 (-) mixture used for its generation can substantially reduce ClO3 (-) concentrations. Switching to purified ClO2 also reduces the concentrations of lipid-bound oleic acid chlorohydrins and protein-bound chlorotyrosines in produce.