Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 55, Issue 21, Pages 14876-14885Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.1c04994
Keywords
food; disinfection byproducts; irrigation; photochemistry; chlorate; bromate
Categories
Funding
- United States Department of Agriculture Commodity Credit Corporation [TASC-2020-10]
- Dried Fruit Association of California through the Technical Assistance for Specialty Crops Program [TASC-2020-10]
- HanWool Scholarship
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The increasing use of chlorine- or chloramine-containing irrigation waters is raising concerns about the formation and uptake of disinfection byproducts into irrigated produce. Sunlight significantly enhances the formation of chlorate from chlorine solutions, but not from chloramine solutions. Vegetables sprayed with chlorine-containing irrigation water in sunlight had chlorate concentrations above maximum residue levels in the EU, while spraying with chloramine-containing water in the dark minimized chlorate formation and uptake.
The increasing use of chlorine- or chloramine-containing irrigation waters to minimize foodborne pathogens is raising concerns about the formation and uptake of disinfection byproducts into irrigated produce. Chlorate has received particular attention in the European Union. While previous research demonstrated the formation of chlorate from dark disproportionation reactions of free chlorine and uptake of chlorate into produce from roots, this study evaluated chlorate formation from solar irradiation of chlorine- and chloramine-containing irrigation droplets and uptake through produce surfaces. Sunlight photolysis of 50 mu M (3.6 mg/L as Cl-2) chlorine significantly enhanced the formation of chlorate, with a 7.2% molar yield relative to chlorine. Chlorate formation was much less significant in sunlit chloramine solutions. In chlorinated solutions containing 270 mu g/L bromide, sunlight also induced the conversion of bromide to 280 mu g/L bromate. Droplet evaporation and the resulting increase in chlorine concentrations approximately doubled sunlight-induced chlorate formation relative to that in the bulk solutions in which evaporation is negligible. When vegetables (broccoli, cabbage, chicory, lettuce, and spinach) were sprayed with chlorine-containing irrigation water in a sunlit field, sunlight promoted chlorate formation and uptake through vegetable surfaces to concentrations above maximum residue levels in the European Union. Spraying with chloramine-containing waters in the dark minimized chlorate formation and uptake into the vegetables.
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