Arsenic mobilisation induced by bacterial iron reduction and competing phosphorous

Dissimilatory Fe reducing bacteria play a fundamental role in catalysing the redox transformations that ultimately control the mobility of As in aquatic environments. In this study we investigated the stability of As retained by Al and Fe (hydr)oxides (hematite, goethite, 24line ferrihydrite, three Al4goethites, gi bbsite, and a poorly crystalline Al hydroxide) under anoxic conditions in the presence of S. putrefaciens cells and phosphate as a competing ion. S. putrefaciens cells were able to bind on mineral surfaces and utilise both noncrystalline and crystalline Fe (hydr)oxides as electron acceptor releasing As into solution. Phosphate competed strongly with arsenate and its efficiency seemed to be governed by the nature of the binding mechanism between As and adsorbent surface. High propotion of sorbed As were desorbed by phosphate from gibbsite followed by Al4goethites. Reflecting its low crystallinity, Al hydroxide was the most efficient in retaining arsenate on its surface followed by ferrihydrite, goethite, and hematite.