Microbial and physicochemical assessment of irrigation water treatment methods

Abstract

Aims: The presence of foodborne pathogens in preharvest agricultural water has been identified as a potential contamination source in outbreak investigations, driving markets and auditing bodies to begin requiring water treatment for high-risk produce. Therefore, it is essential that we identify water treatment methods which are effective as well as practical in their application on farm. Methods and Results: In this work, we evaluated two sanitizers which are most prominent in preharvest agricultural water treatment (calcium hypochlorite (free chlorine: 3-5 ppm) and peracetic acid (PAA: 5 ppm)), an EPA registered antimicrobial device (ultraviolet light (UV)), in addition to a combination approach (chlorine + UV, PAA + UV). Treatments were evaluated for their ability to inactivate total coliforms and generic Escherichia coli and consistency in treatment efficacy over 1 h of operation. Physicochemical variables were measured along with microbial populations at 0, 5, 15, 30, 45 and 60 min of operation. Escherichia coli and coliform counts showed a significant (P < 0Á05) reduction after treatment, with combination and singular treatments equally effective at inactivating E. coli and coliforms. A significant increase (P < 0Á05) in oxidation-reduction potential was seen during water treatment (Chlorine; UV + Chlorine), and a significant reduction (P < 0Á05) in pH was seen after PAA and PAA + UV treatments (60 min). Conclusion: Overall, the results indicate that all treatments evaluated are equally efficacious for inactivating E. coli and coliforms present in surface agricultural water. Significance and Impact of the Study: This information when paired with challenge studies targeting foodborne pathogens of interest can be used to support grower decisions when selecting and validating a preharvest agricultural water treatment programme.

Contaminated water and the Food Safety Modernization Act

“…LGMA recognizes several methods for water treatment including physical devices such as heat sterilization and ultraviolet light (UV) and chemicals like chlorine dioxide or peroxyacetic acid (Rock 2020). Following Krishnan et al (2021), we assume that applying chlorine to water is the most common agricultural water treatment method. According to the CDC (2022a) adding 0.5 mg/l free chlorine to water for less than 30 minutes reduces the concentration of E. coli by 99.99%.…”