title: Mobilization of arsenic in aquifers from the Datong Basin, China: evidence from geochemical and iron isotopic data.
abstract: Iron isotope compositions of various Fe pools in aquifer sediments were measured at a known As-contaminated site in the Datong Basin, China. The δ(56)Fe values of HCl-extracted poor-crystalline Fe(III) range widely from -0.41‰ to 0.36‰. We interpret the low Fe(II)/Fe(Extractable) ratios (<50%) and the negative correlation between Fe(II)/Fe(Extractable) and δ(56)Fe values in HCl-extracted poor-crystalline Fe to be best explained by redox cycling of Fe induced by microbial Fe(III) reduction. However, the high Fe(II)/Fe(Extractable) ratios (~/>70%) and positive correlation between Fe(II)/Fe(Extractable) and δ(56)Fe values for HCl-extracted poor-crystalline Fe indicates production of sulfides (FeSs). The δ(56)Fe values of crystalline Fe(III) extracted by reductant appears to be comparatively small varying from -0.01‰ to 0.24‰, which is consistent with the δ(56)Fe values for ferric oxides/hydroxides having undergone microbial Fe(III) reduction. The Fe isotope composition of various Fe pools shows the transformation between crystalline Fe(III) and poor-crystalline crystalline Fe(III) and the secondary Fe(II) phases has already occurred or is occurring in aquifer sediments. More importantly, there is a significant difference in the As concentrations in crystalline Fe(III) oxides/hydroxides and HCl-extracted Fe phases. The concentrations of As range from 1.6 to 29.9 mg kg(-1) and from 0.6 to 3.0 mg kg(-1), for crystalline Fe(III) and HCl-extracted Fe phases respectively. Accordingly, the transformation of Fe minerals induced by microbial Fe(III) reduction can contribute to the mobilization of As. This study is the first to examine the Fe isotope compositions in high As aquifer sediments; the results show that the Fe isotope would be an important tool in demonstrating the enrichment of As in groundwater.
authors.affiliation: School of Environmental Studies & State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 430074 Wuhan, China. xjxie@cug.edu.cn
authors.forename: Xianjun
authors.initials: X
authors.lastname: Xie
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Johnson
authors.forename: Yanxin
authors.initials: Y
authors.lastname: Wang
authors.forename: Craig C
authors.initials: CC
authors.lastname: Lundstrom
authors.forename: Andre
authors.initials: A
authors.lastname: Ellis
authors.forename: Xiangli
authors.initials: X
authors.lastname: Wang
authors.forename: Mengyu
authors.initials: M
authors.lastname: Duan
mesh_terms: D001151:Arsenic / Q000032:analysis* / Q000737:chemistry; D002681:China; D004784:Environmental Monitoring; D060587:Groundwater / Q000737:chemistry*; D007501:Iron / Q000032:analysis / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry
chemical_list: D014874:Water Pollutants, Chemical; D007501:Iron; D001151:Arsenic