Pb(II) distributions at biofilm-metal oxide interfaces

The distribution of aqueous Pb(II) sorbed at the interface between Burkholderia cepacia biofilms and hematite (alpha -Fe2O3) or corundum (alpha -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-alpha 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 alpha -Fe2O3 (0001) > alpha -Al2O3 (11-over-bar-02) > alpha -Al2O3 (0001), despite the greater site density within the overlying biofilms. At [Pb] > 10(-6) M, significant Pb uptake by the biofilms was observed.