Depletion of free chlorine and generation of trichloromethane in the presence of pH control agents in chlorinated water at pH 6.5

Authors: Fan, Xuetong; Gurtler, Joshua

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2024
Publication Date: 5/9/2024
Citation: Fan, X., Gurtler, J. 2024. Depletion of free chlorine and generation of trichloromethane in the presence of pH control agents in chlorinated water at pH 6.5. Journal of Food Protection. 87(7):100296. https://doi.org/10.1016/j.jfp.2024.100296.
DOI: https://doi.org/10.1016/j.jfp.2024.100296

Interpretive Summary: To maximize the antimicrobial efficacy of chlorine, a common sanitizer used by the produce industry, the pH of chlorinated water is often adjusted using citric acid. Earlier studies by ARS scientists and others have demonstrated that citric acid reacts with chlorine forming high amounts of trichloromethane, a probable carcinogen. However, it is unclear if other organic or inorganic acidifiers can be used to replace citric acid. The objective of this study was to determine the reactivity of 14 organic and inorganic pH control agents with chlorine and generation of trichloromethane. Results showed that inorganic acids and many organic acids other than citric and malic acids maintained the levels of chlorine in wash water, and led to little formation of trichloromethane. Therefore, it is recommended to the industry that inorganic acids and certain organic acids should replace citric acid as pH control agents in chlorinated water to stabilize the chlorine level in the wash water, and minimize the formation of undesirable chlorine byproducts.

Technical Abstract: Chlorine is commonly used by the fresh produce industry to sanitize water and minimize pathogen cross-contamination during handling. To maximize the antimicrobial efficacy of chlorine, the pH of chlorinated water is often reduced to values of pH 6-7 with citric acid. Earlier studies have demonstrated that citric acid reacts with chlorine forming high amounts of trichloromethane, a major chlorine byproduct in water. However, it is unclear if other organic or inorganic acidifiers can replace citric acid to minimize the formation of trichloromethane. The objective of the present study was to determine the reactivity of organic and inorganic pH control agents with chlorine to generate trichloromethane. Chlorine (~100 ppm) was mixed with 10 mM of each of twelve organic acids (citric acid, malic acid, tartaric acid, acetic acid, lactic acid, ascorbic acid, dehydroascorbic acid, propionic acid, adipic acid, succinic acid, fumaric acid or levulinic acid) and two inorganic pH control agents (sodium acid sulfate and phosphoric acid) to effect a pH level of 6.5. Free chlorine levels and trichloromethane concentrations were measured over 3 h at 3°C and 22°C. Results demonstrated that ascorbic acid, dehydroascorbic acid, citric acid and malic acid rapidly depleted levels of free chlorine at both temperatures of 22°C and 3°C while tartaric acid and lactic acid decreased chlorine levels more slowly during 3 h of incubation at 22°C. Using citric acid as a pH control agent led to the formation of significantly higher concentrations of trichloromethane than other acids. Even though ascorbic acid, dehydroascorbic acid and malic acid rapidly depleted chlorine, low or no significant concentrations of trichloromethane were formed. Chloroacetones were also found in chlorinated water in the presence of citric acid and ascorbic acid. Other acids did not result in the formation of chloroacetones. Our results demonstrated that inorganic acids and some organic acids can be used to replace citric acid as pH control agents in chlorinated water.