Synchrotron X-ray studies of heavy metal mineral-microbe interactions

THE availability of analytical methods that utilize the very intense and bright X-rays from synchro- tron radiation sources has fundamentally changed the way in which geoscientists, environmental scientists and soil scientists study complex environmental samples and decipher the chemical and biological processes that impact the specia- tion, transport and potential bioavailability of environmental toxins (Brown et al., 2006). Such samples are often mixtures of crystalline and amorphous phases in particle-sizes ranging from cm to nm, adsorbed metal ions and organic molecules, natural organic matter, microbial organisms, algae, plant materials and aqueous solutions. The processes that affect the chemical forms and environmental fate of contaminants in such mixtures range from surface adsorption, desorption, precipitation and dissolution reac- tions, often involving a combination of hydro- lysis, ligand exchange and electron transfer, to biological interactions in which microbial organ- isms, algae or plants interact with mineral surfaces and environmental contaminantform such contaminants into more (or less) toxic forms; and (3) mineral dissolution reactions, which can release heavy metal and metalloid contaminants. Determining the effects of these processes on environmental contaminants