XAFS and XSW study of the distribution of Pb(II) sorbed to biofilms on α-Al2O3 and α-FeOOH surfaces

Abstract

Biofilms form ubiquitous organic coatings on mineral surfaces in soil and aquatic environments. In order to understand the chemical speciation of heavy metals (such as Pb) sorbed to minerals colonized by bacteria, it is essential to evaluate the coupled biotic and abiotic sorption by such heterogeneous systems. We have used EXAFS spectroscopy to quantitatively determine the partitioning of Pb between biofilms (Burkholderia cepacia) and the reactive sites on powdered α-Al2O3 and α-FeOOH. We have also used x-ray standing wave (XSW) methods to study the distribution of Pb sorbed to biofilms grown on the surface of single crystal α-Al2O3 (1-102). The XSW data show that Pb occurs dominantly at the α-Al2O3 (1-102) surface at low [Pb]T and is more distributed within the biofilm at higher [Pb]T. The Pb LIII EXAFS data show that Pb is partitioned more strongly to the α-FeOOH surface than the α-Al2O3 surface relative to the biofilm. However, the fraction of Pb sorbed to the α-Al2O3 mineral surface relative to the biofilm may increase as Pb coverage increases.