title: Natural inactivation of Escherichia coli in anaerobic and reduced groundwater.
abstract: OBJECTIVE
  Inactivation rates of Escherichia coli in groundwater have most often been determined in aerobic and oxidized systems. This study examined E. coli inactivation rates in anaerobic and extremely reduced groundwater systems that have been identified as recharge zones.
  
  
  RESULTS
  Groundwater from six artesian wells was diverted to above-ground, flow-through mesocosms that contained laboratory grown E. coli in diffusion chambers. All groundwater was anaerobic and extremely reduced (ORP < -300 mV). Cells were plated onto mTEC agar during 21-day incubation periods. All data fit a bi-phasic inactivation model, with >95% of the E. coli population being inactivated <11·0 h (mean k = 0·488 ±0·188 h(-1) ).
  
  
  CONCLUSIONS
  The groundwater geochemical conditions enhanced the inactivation of E. coli to rates approx. 21-fold greater than previously published inactivation rate in groundwater (mean k = 0·023 ± 0·030 h(-1) ). Also, mTEC agar inhibits E. coli growth following exposure to anaerobic and reduced groundwater.
  
  
  CONCLUSIONS
  Aquifer recharge zones with geochemical characteristics observed in this study complement above-ground engineered processes (e.g. filtration, disinfection), while increasing the overall indicator micro-organism log-reduction rate of a facility.
authors.affiliation: US Geological Survey, St. Petersburg Coastal & Marine Science Center, St. Petersburg, FL, USA.
authors.forename: J T
authors.initials: JT
authors.lastname: Lisle
mesh_terms: D000693:Anaerobiosis; D004203:Disinfection / Q000379:methods*; D004926:Escherichia coli / Q000254:growth & development*; D060587:Groundwater / Q000737:chemistry / Q000382:microbiology*; D008962:Models, Theoretical; D010084:Oxidation-Reduction
keywords: Escherichia coli (all potential pathogenic types); cell injury; disinfection; stress response; water