Sodium chlorite treatments in irrigation water are a significant source of chlorate and perchlorate in hop cones

Authors: Gonzalez Tapia, Francisco; WALSH, DOUGLAS - Washington State University; GROENENDALE, DANIEL - Washington State University

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2025
Publication Date: 6/18/2025
Citation: Gonzalez Tapia, F., Walsh, D.B., Groenendale, D.P. 2025. Sodium chlorite treatments in irrigation water are a significant source of chlorate and perchlorate in hop cones. Journal of the American Society for Horticultural Science. 150(4):182-190. https://doi.org/10.21273/JASHS05493-25.
DOI: https://doi.org/10.21273/JASHS05493-25

Interpretive Summary: Hops are a key ingredient in beer production, and ensuring their quality and safety is critical for growers and brewers alike. Many hop producers use chlorine-based drip line cleaners to maintain irrigation systems, but these products can leave behind chemical residues that raise regulatory concerns, particularly for exports to the European Union. Chlorate and perchlorate have been associated with disrupting iodine uptake in the thyroid gland in vulnerable populations. This study examined the effects of different cleaning treatments, including sodium chlorite and non-chlorine alternatives, on chlorate and perchlorate residues in hop cones and soil over two growing seasons. Our findings revealed that continuous use of sodium chlorite significantly increased chlorate residues in hop cones, exceeding European Union safety limits by a large margin. Even treatments with occasional sodium chlorite applications resulted in notable chlorate accumulation. Perchlorate levels were also elevated but remained within European Union limits. Interestingly, soil samples from sodium chlorite-treated plots contained more perchlorate but no detectable chlorate, suggesting that hop plants readily absorb chlorate from soil water. In contrast, using hydrogen peroxide and peroxyacetic acid as alternative cleaning agents led to a substantial reduction in these residues within a single year. These results suggest that shifting away from chlorine-based cleaners can help growers meet international safety standards while maintaining effective irrigation system management. Furthermore, regulatory agencies may need to reconsider the strict limits on chlorate in hops, as current thresholds appear far lower than necessary to pose health risks to individuals that commonly consume beer. By adopting safer irrigation cleaning methods and reassessing chlorate regulations, the hop industry can ensure both food safety and continued global trade.

Technical Abstract: Chlorine-based drip line cleaners have been widely used in hop (Humulus lupulus) production to prevent biofilm buildup in irrigation systems. However, concerns have emerged regarding chlorate (ClO3') and perchlorate (ClO4') residues in hop cones due to their associated risk of disrupting iodine uptake in the thyroid gland in vulnerable populations. This study, conducted in 2023 and 2024 at Washington State University’s Irrigated Agriculture Research and Extension Center, evaluated the impact of chlorine-based and non-chlorine-based irrigation system cleaning treatments on hop cone and soil chlorate and perchlorate levels. Treatments included continuous 2 ppm sodium chlorite application, shock 25 ppm sodium chlorite application, a combination of both, and a hydrogen peroxide/peroxyacetic acid as the control – current grower standard. Our findings indicated that continuous sodium chlorite application led to significant chlorate accumulation in hop cones, reaching up to 47 mg kg'¹, exceeding the European Union (EU) maximum residue limit (MRL) of 0.05 mg kg'¹ by nearly 1,000-fold. Perchlorate residues remained below the EU MRL of 0.75 mg kg'¹ but increased with sodium chlorite applications. Soil analysis revealed perchlorate presence in sodium chlorite-treated plots, while chlorate was undetectable in soil but highly concentrated in hop cones, suggesting strong uptake by hop plants. Eliminating chlorine-based cleaners reduced chlorate residues by up to 88% within one year. These findings highlight the risks associated with chlorine-based cleaning agents in irrigation systems, particularly for international trade compliance. The study suggests that non-chlorine alternatives effectively mitigate chlorate and perchlorate accumulation while maintaining irrigation efficacy. Given the significant disparity between chlorate MRLs and realistic exposure risks, regulatory reassessment of chlorate limits in hops may be warranted to balance food safety and trade feasibility.