ARS | Publication request: The 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: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 5, 2011
Publication Date: March 5, 2012
Citation: Ingram, D.T., Callahan, M.L., Ferguson, S.E., Hoover, D., Shelton, D.R., Millner, P.D., Patel, J.R., Kniel, K., Sharma, M. 2012. The use of Zero-valent iron biosand filters to reduce E. coli O157:H12 in irrigation water applied to spinach plants in a field setting. Journal of Applied Microbiology. 112(3):551-560.

Interpretive Summary: One source of contamination of fresh produce is the surface water used for irrigation. Zerovalent iron may provide a cost effective mechanism to reduce the dissemination of pathogens introduced to produce via contaminated water. These experiments are the first to evaluate the efficiacy of zerovalent iron irrigation water decontamination at the field scale. Biosand filters containing sand (S), or sand and zerovalent iron (SI), were constructed at the field site. E coli O157:H12 was inoculated into the irrigation water and filtered through either S or SI columns. On day 0, right after inoculation of water, SI columns were significantly more effective at killing and removing high numbers of E. coli from irrigation water than S columns. Spinach planted at the site was irrigated with contaminated (untreated) water, or water filtered through either S or SI columns. Spinach irrigated with SI-filtered water had an approximate ten-to one hundred thousand-fold decrease when compared to plants irrigated with untreated water or the S-filtered water. Overall, our results show that zerovalent iron can be effective in reducing the potential dissemination of foodborne pathogens via contaminated water. This may provide a simple and relatively cost-effective method for smaller growers and farmers to decontaminate irrigation water.

Technical Abstract: Contaminated irrigation water is a potential source for the introduction of foodborne pathogens on to produce commodities. Zero-valent iron (ZVI) may provide a simple cheap method to mitigate the contamination of produce groups through irrigation water. A small field scale system was utilized to evaluate the effectiveness of a Biosand filter (S), a biosand filter with ZVI incorporated (SI), and a control (no treatment). An inoculum of ca. 8.5 log CFU/100 ml of the non-pathogenic surrogate E. coli O157:H12 was introduce to all three column treatments. Filters containing ZVI inactivated ca. 6 log CFU/100 ml during filtration, significantly more (P < 0.05) than S filter (1 log CFU/100 ml) when compared to initial inoculum levels on day 0. Inoculated, filtered water collected from sprinkler emitters also revealed similar resutsl. Water filtered through ZVI and S columns were also used to overhead-irrigate spinach. Spinach plants irrigated with SI-filtered water has significantly lower E. coli O157 counts (0.13 log CFU/g) counts than spinach irriated with S-filtered water (4.37 log CFU/g) or spinach irrigated with control (5.23 log CFU/g). Water, spinach plant and soil samples were obtained on 0, 1, 4, 6, 8, 10, 13 and 15 were taken and analyzed. E. coli O157:H12 cells filtered through SI persistence for the shortest durations in soil, while E. coli counts in the control and S-filtered were statistically similar. Overall, the zero-valent irom may be a cost effective mitigation step to help small farmers reduce risk to consumers.