Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/13/2009
Publication Date: 6/15/2009
Publication URL: http://www.ars.usda.gov/SP2UserFiles/Place/53102000/pdf_pubs/P2276.pdf
Citation: Kim, H., Bradford, S.A., Walker, S. 2009. Escherichia coli O157:H7 Transport in Saturated Porous Media: Role of Solution Chemistry and Surface Macromolecules. Journal of Environmental Science & Technology, 43(12):4340-4347. Interpretive Summary: Escherichia coli O157:H7 has been associated with food- and water-borne disease outbreaks in the United States. The objective of this study was to systematically investigate the influence of surface macromolecules on the transport of Escherichia coli O157:H7 in saturated porous media over a range of solution chemistries. Results indicated that bacteria retention in the sand was not consistent with existing theory to describe chemical interactions between the sand and the cells, but could be explained by solution chemistry dependent changes in the shape of the macromolecules on the surface of the bacteria. The retention mechanism of the cells in the porous media was found to be a complex function that depends on the solution chemistry, cell-cell interactions, and the pore structure. The findings in this study suggest that previous work conducted at lower pH and ionic strength conditions may underestimate E. coli O157:H7 travel distance in higher salt and pH groundwater environments.
Technical Abstract: The transport and deposition behavior of Escherichia coli O157:H7 was investigated in saturated packed-bed columns and micromodel systems over a range of ionic strength (IS) (1, 10, and 100 mM) and pH (5.8, 8.4, and 9.2). At a given IS, enhanced solution pH resulted in decreased deposition as a result of the increase in the measured zeta potential of the quartz sand . This deposition trend was consistent with predictions from classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Conversely, the E. coli O157:H7 deposition was inversely proportional to IS (1–100 mM) at high pH conditions (8.4 and 9.2), whereas no effect of IS was observed at pH 5.8. This deposition trend was not consistent with DLVO theory, but could be explained by pH-associated electrosteric stabilization. This phenomenon is closely related to the pH-dependent protonated state of functional groups on E. coli O157:H7 surface macromolecules and the corresponding conformational state of the bacterial polymers. Results from this study demonstrate that retention of E. coli O157:H7 cell in porous media is a complex function that depends on the solution chemistry, cell-cell interactions, and pore structure. The findings in this study also imply that previous work conducted at lower pH and IS conditions may underestimate E. coli O157:H7 travel distance in higher salt and pH groundwater environments.