| Abstract
| - Reduction of arsenate As(V) and As-bearing Fe (hydr)oxides have been proposed as dominant pathways of Asrelease within soils and aquifers. Here we examine As elutionfrom columns loaded with ferrihydrite-coated sandpresorbed with As(V) or As(III) at circumneutral pH uponFe and/or As reduction; biotic stimulated reduction is thencompared to abiotic elution. Columns were inoculatedwith Shewanella putrefaciens strain CN-32 or Sulfurospirillumbarnesii strain SES-3, organisms capable of As(V) and Fe(III) reduction, or Bacillus benzoevorans strain HT-1, anorganism capable of As(V) but not Fe(III) reduction. On thebasis of equal surface coverages, As(III) elution fromabiotic columns exceeded As(V) elution by a factor of 2;thus, As(III) is more readily released from ferrihydrite underthe imposed reaction conditions. Biologically mediated As-reduction induced by B. benzoevorans enhances therelease of total As relative to As(V) under abiotic conditions.However, under Fe reducing conditions invoked byeither S. barnesii or S. putrefaciens, approximately threetimes more As (V or III) was retained within column solidsrelative to the abiotic experiments, despite appreciabledecreases in surface area due to biotransformation of solidphases. Enhanced As sequestration upon ferrihydritereduction is consistent with adsorption or incorporation ofAs into biotransformed solids. Our observations indicatethat As retention and release from Fe (hydr)oxide(s) iscontrolled by complex pathways of Fe biotransformationand that reductive dissolution of As-bearing ferrihydrite canpromote As sequestration rather than desorption underconditions examined here.
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