Pb(II) distributions at biofilm–metal oxide interfaces

^*Geological and Environmental Sciences and ^§Civil and Environmental Engineering, Stanford University, Stanford, CA 94035-2115; ^‡School of Natural Resources, Ohio State University, Columbus, OH 43210; ^¶Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, 2575 Sand Hill Road, Menlo Park, CA 94025

Edited by Joseph V. Smith, University of Chicago, Chicago, IL, and approved July 25, 2001 (received for review March 28, 2001)

Abstract

The distribution of aqueous Pb(II) sorbed at the interface between Burkholderia cepacia biofilms and hematite (α-Fe₂O₃) or corundum (α-Al₂O₃) surfaces has been probed by using an application of the long-period x-ray standing wave technique. Attached bacteria and adsorbed organic matter may interfere with sorption processes on metal oxide surfaces by changing the characteristics of the electrical double layer at the solid–solution interface, blocking surface sites, or providing a variety of new sites for metal binding. In this work, Pb L_α fluorescence yield profiles for samples equilibrated with 10⁻⁷ to 10^−3.8 M Pb(II) were measured and modeled to determine quantitatively the partitioning of Pb(II) at the biofilm–metal oxide interface. Our data show that the reactive sites on the metal oxide surfaces were not passivated by the formation of a monolayer biofilm. Instead, high-energy surface sites on the metal oxides form the dominant sink for Pb(II) at submicromolar concentrations, following the trend α-Fe₂O₃ (0001) > α-Al₂O₃ (11̄02) > α-Al₂O₃ (0001), despite the greater site density within the overlying biofilms. At [Pb] > 10⁻⁶ M, significant Pb uptake by the biofilms was observed.

Footnotes

↵ † To whom reprint requests should be addressed. E-mail: alexis{at}pangea.stanford.edu.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

XSW,

x-ray standing wave;

S/B ratio,

[(surface Pb)/(biofilm Pb)];

FY,

fluorescence yield