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

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