ARS | Publication request: Use of zero-valent iron biosand filters to reduce E. coli O157:H12 in irrigation water applied to spinach plants in a field setting

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: December 5, 2011
Publication Date: December 5, 2012
Citation: Ingram, D.T., Hoover, D., Shelton, D.R., Millner, P.D., Patel, J.R., Kniel, K., Sharma, M. 2012. Use of zero-valent iron biosand filters to reduce E. coli O157:H12 in irrigation water applied to spinach plants in a field setting. International Association for Food Protection. 112:551-560.

Technical Abstract: Introduction: Zero-valent iron (ZVI) filters may provide an efficient method to mitigate the contamination of produce crops through irrigation water. Purpose: To evaluate the use of ZVI-filtration in decontaminating E. coli O157:H12 in irrigation water and on spinach plants in a small, field-scale trial. Methods: A field-scale system was utilized to evaluate the effectiveness of a biosand filter (S), a biosand filter with zero valent iron incorporated (ZVI), and a control (C, no treatment) in decontaminating irrigation water. An inoculum of ca. 8.5 log CFU/ 100 ml of nalidixic acid resistant Escherichia coli O157:H12 was introduced to all three column treatments in 20-L doses. Filtered waters were subsequently overhead irrigated to ‘Tyee’ spinach plants. Water, spinach plant and soil samples were obtained on days 0, 1, 4, 6, 8, 10, 13 and 15 and analyzed for E. coli O157:H12 populations through direct plating on MacConkey agar or through Most Probable Number assay. Results: ZVI filters inactivated ca. 6 log CFU/ 100ml E. coli O157:H12 during filtration on day 0, significantly (P < 0.05) more than S filter (0.49 CFU/ 100ml) when compared to control on day 0 (8.3 log CFU/ 100ml). On day 0, spinach plants irrigated with ZVI-filtered water had significantly lower E. coli O157 counts (0.13 log CFU/g) than spinach irrigated with either S-filtered (4.37 log CFU/g) or control (5.23 log CFU/g) water. Soils irrigated with ZVI-filtered water contained E. coli O157:H12 populations below the detection limit (2 log CFU/g), while those irrigated with S-filtered water (3.56 log CFU/g) were significantly lower than those irrigated with control (4.64 log CFU/g). Significance: Zero-valent ion treatment may be a cost-effective mitigation step to help small farmers reduce risk of foodborne E. coli infections associated with contamination of leafy greens.