title: Use of zero-valent iron biosand filters to reduce Escherichia coli O157:H12 in irrigation water applied to spinach plants in a field setting.
abstract: OBJECTIVE
  Zero-valent iron (ZVI) filters may provide an efficient method to mitigate the contamination of produce crops through irrigation water.
  
  
  METHODS
  A field-scale system was utilized to evaluate the effectiveness of a biosand filter (S), a biosand filter with ZVI incorporated (ZVI) and a control (C, no treatment) in decontaminating irrigation water. An inoculum of c.8·5log CFU100ml(-1) of 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 analysed for E. coli O157:H12 populations.
  
  
  RESULTS
  ZVI filters inactivated c.6logCFU100ml(-1) E. coli O157:H12 during filtration on day 0, significantly (P<0·05) more than S filter (0·49CFU100ml(-1)) when compared to control on day 0 (8·3log CFU100ml(-1)). On day 0, spinach plants irrigated with ZVI-filtered water had significantly lower E. coli O157 counts (0·13logCFUg(-1)) than spinach irrigated with either S-filtered (4·37logCFUg(-1)) or control (5·23logCFUg(-1)) water. Soils irrigated with ZVI-filtered water contained E. coli O157:H12 populations below the detection limit (2logCFUg(-1)), while those irrigated with S-filtered water (3·56logCFUg(-1)) were significantly lower than those irrigated with control (4·64logCFUg(-1)).
  
  
  CONCLUSIONS
  ZVI biosand filters were more effective in reducing E. coli O157:H12 populations in irrigation water than sand filters.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Environmental Microbial and Food Safety Laboratory, Animal and Natural Resources Institute, Henry A Wallace Beltsville Area Research Center, Beltsville, MD 20705, USA.
authors.forename: D T
authors.initials: DT
authors.lastname: Ingram
authors.forename: M T
authors.initials: MT
authors.lastname: Callahan
authors.forename: S
authors.initials: S
authors.lastname: Ferguson
authors.forename: D G
authors.initials: DG
authors.lastname: Hoover
authors.forename: P C
authors.initials: PC
authors.lastname: Chiu
authors.forename: D R
authors.initials: DR
authors.lastname: Shelton
authors.forename: P D
authors.initials: PD
authors.lastname: Millner
authors.forename: M J
authors.initials: MJ
authors.lastname: Camp
authors.forename: J R
authors.initials: JR
authors.lastname: Patel
authors.forename: K E
authors.initials: KE
authors.lastname: Kniel
authors.forename: M
authors.initials: M
authors.lastname: Sharma
mesh_terms: D057914:Agricultural Irrigation; D000383:Agriculture / Q000379:methods*; D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000254:growth & development / Q000302:isolation & purification*; D005374:Filtration; D005506:Food Contamination / Q000517:prevention & control*; D005516:Food Microbiology; D007501:Iron / Q000737:chemistry*; D018515:Plant Leaves / Q000382:microbiology; D012988:Soil Microbiology; D018724:Spinacia oleracea / Q000382:microbiology*; D014871:Water Microbiology
chemical_list: D007501:Iron