Purpose: This study evaluated overhead and drip irrigation as well as chlorine dioxide water treatment on pathogen presence (E. coli O157 and Salmonella) and indicator organism levels (fecal coliforms and generic E. coli) within an organic farming system.
Methods: Irrigation water from a creek was sampled at the source, prior to filtration and chlorine dioxide treatment. Replicate lettuce plots, amended with broiler litter, were randomly assigned: untreated overhead or drip irrigation and chlorine dioxide treated overhead or drip irrigation. Samples from agricultural inputs (288 water, 128 soil, 44 potting mix, 43 transplants) and lettuce (n = 275) were quantified for indicator organisms and for E. coli O157 and Salmonella isolation.
Results: In both years of the study, fecal coliform levels were reduced (at least 1 log MPN/100 ml) at the point of irrigation water application when a chlorine dioxide treatment system was used. However, fecal coliforms and generic E. coli levels were similar in the soil and from lettuce harvested from untreated and treated plots. Several Salmonella serovars (Oranienburg; Livingstone; Tennessee, and Infantis) and E. coli O157:H7 were isolated from potting soil and transplant plugs (Salmonella Mbandaka, Minnesota, Ealing). E. coli O157:H7 was detected in creek samples (1/54) and in the irrigation line after the filter (1/25). One untreated drip irrigation sample (1/37) and two untreated overhead irrigation samples (2/36) were positive for E. coli O157:H7. E. coli O157:H7 was detected on lettuce from treated drip (1/64) and untreated (3/128) overhead and drip irrigation plots.
Significance: Use of chlorine dioxide water treatment appeared to reduce indicator levels in water and may have reduced pathogen contamination in lettuce.