Evaluation of Escherichia coli and Coliforms in Aquaponic Water for Produce Irrigation

Abstract

With the increase of commercialized aquaponics, concerns associated with pathogens in aquaculture water transferring to the produce have increased. The FDA Produce Safety Rule states water used for irrigation purposes that is likely to come into contact with the edible portion of the fruit and vegetables must not exceed a defined limit of Escherichia coli in the water. It requires a geometric mean (GM) and a statistical threshold (STV) of 126 or less and 410 CFU or less of generic E. coli/100 mL of irrigation water, respectively. Even though aquaponics has not been included in this guideline, it creates a baseline for aquaponic facilities to reference if monitoring the water. A one-year evaluation was completed to identify points in the aquaponics system in which the microbial profile changed and to determine whether the water used on produce followed the FDA Produce Safety Rule. Water was sampled and analyzed at six points in the system in which the E. coli and coliforms profile was likely to change. The GM and STV were calculated based on the irrigation source, determining the water collected from February 1 to May 31, 2019 had E. coli populations below the FDA limit and from June 1, 2019 to January 31, 2020, the E. coli populations were above the FDA limit. From this study it was concluded that from June to January water must be monitored more closely in an aquaponics system to ensure safety of the produce. A microbial analysis was performed on a nutrient film technique (NFT) system using aquaponic water over an initial 16-d growth cycle of butterhead lettuce. Three sump tanks contained aquaponic water and one contained a hydroponic control that was applied to the lettuce roots continuously. Water samples were collected on d 0, 4, 8, 12, and 16 followed by microbial isolation for E. coli and coliforms. The E. coli and coliforms populations decreased as holding time increased and the E. coli population was within the FDA Produce Safety Rule on d 8. From these results, in order to ensure proper reduction of E. coli, the water must be held for at least 8 d and can be help up to 16 d before changing the water out.