title: Microbes enhance mobility of arsenic in pleistocene aquifer sand from Bangladesh.
abstract: Dissimilatory metal-reducing bacteria can mobilize As, but few studies have studied such processes in deeper orange-colored Pleistocene sands containing 1-2 mg kg(-1) As that are associated with low-As groundwater in Bangladesh. To address this gap, anaerobic incubations were conducted in replicate over 90 days using natural orange sands initially containing 0.14 mg kg(-1) of 1 M phosphate-extractable As (24 h), >99% as As(V), and 0.8 g kg(-1) of 1.2 M HCl-leachable Fe (1 h at 80 °C), 95% as Fe(III). The sediment was resuspended in artificial groundwater, with or without lactate as a labile carbon source, and inoculated with metal-reducing Shewanella sp. ANA-3. Within 23 days, dissolved As concentrations increased to 17 μg L(-1) with lactate, 97% as As(III), and 2 μg L(-1) without lactate. Phosphate-extractable As concentrations increased 4-fold to 0.6 mg kg(-1) in the same incubations, even without the addition of lactate. Dissolved As levels in controls without Shewanella, both with and without lactate, instead remained <1 μg L(-1). These observations indicate that metal-reducers such as Shewanella can trigger As release to groundwater by converting sedimentary As to a more mobilizable form without the addition of high levels of labile carbon. Such interactions need to be better understood to determine the vulnerability of low-As aquifers from which drinking water is increasingly drawn in Bangladesh.
authors.affiliation: School of Earth and Environmental Sciences, Queens College, City University of New York 65-30, Kissena Blvd, Flushing, New York 11367, United States. rdhar@york.cuny.edu
authors.forename: Ratan K
authors.initials: RK
authors.lastname: Dhar
authors.forename: Yan
authors.initials: Y
authors.lastname: Zheng
authors.forename: Chad W
authors.initials: CW
authors.lastname: Saltikov
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Radloff
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Mailloux
authors.forename: Kazi M
authors.initials: KM
authors.lastname: Ahmed
authors.forename: Alexander
authors.initials: A
authors.lastname: van Geen
mesh_terms: D001151:Arsenic / Q000032:analysis / Q000378:metabolism*; D001459:Bangladesh; D005618:Fresh Water / Q000737:chemistry / Q000382:microbiology*; D019015:Geologic Sediments / Q000737:chemistry / Q000382:microbiology*; D007501:Iron / Q000378:metabolism; D020592:Shewanella / Q000378:metabolism; D012822:Silicon Dioxide / Q000737:chemistry; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000378:metabolism*; D014881:Water Supply / Q000032:analysis
chemical_list: D014874:Water Pollutants, Chemical; D012822:Silicon Dioxide; D007501:Iron; D001151:Arsenic