Purpose: To examine open surface waters as a potential source of microbial contamination for produce farming systems, three water systems in Washington were monitored for pathogen presence and indicator organism levels over two years.
Methods: Sampling sites were selected based on stakeholder input to collect monitoring data that would be beneficial to local producers. Site A (8 sampling sites and 18 sampling dates), Site B (14 sampling sites and 13 sampling dates) and Site C (16 sampling sites and 12 sampling dates) represented three different geographic regions in Washington. Samples were quantified for fecal coliforms and generic Escherichia coli using a five-tube most probable number technique, and analyzed for pathogen presence (E. coli Ol57, Salmonella). Washington Department of Ecology (WA-DOE) utilizes a water quality standard for secondary contact recreation water of < 2.3 log colonies/100 ml fecal coliforms and the Leafy Greens Marketing Agreement (LGMA) recommends <2.37 log MPN/100 ml generic E. coli for foliar irrigation application.
Results: Pathogen prevalence (E. coli O157 and Salmonella) ranged from 5.2% (5 pathogen positives) at Site A to 6.9% (14 pathogen positives) at Site C. At Site A, 5 pathogen positives were observed when both the WA-DOE fecal coliform standard and LGMA E. coli standard were met, and only 1 pathogen positive was observed when both standards were exceeded. Alternatively, both Sites B and C had 5 pathogen positives observed when both WA-DOE and LGMA standards were exceeded. Site B had 6 pathogen positives when only the WA-DOE fecal coliform standard was exceeded and Site C had 9 pathogen positives when only the WA-DOE fecal coliform standard was exceeded.
Significance: Meeting indicator organism standards may not accurately reflect pathogen risk. Emphasis on good agricultural practices and risk assessment for irrigation water management programs is warranted.