title: Organic carbon and reducing conditions lead to cadmium immobilization by secondary Fe mineral formation in a pH-neutral soil.
abstract: Cadmium (Cd) is of environmental relevance as it enters soils via Cd-containing phosphate fertilizers and endangers human health when taken up by crops. Cd is known to associate with Fe(III) (oxyhydr)oxides in pH-neutral to slightly acidic soils, though it is not well understood how the interrelation of Fe and Cd changes under Fe(III)-reducing conditions. Therefore, we investigated how the mobility of Cd changes when a Cd-bearing soil is faced with organic carbon input and reducing conditions. Using fatty acid profiles and quantitative PCR, we found that both fermenting and Fe(III)-reducing bacteria were stimulated by organic carbon-rich conditions, leading to significant Fe(III) reduction. The reduction of Fe(III) minerals was accompanied by increasing soil pH, increasing dissolved inorganic carbon, and decreasing Cd mobility. SEM-EDX mapping of soil particles showed that a minor fraction of Cd was transferred to Ca- and S-bearing minerals, probably carbonates and sulfides. Most of the Cd, however, correlated with a secondary iron mineral phase that was formed during microbial Fe(III) mineral reduction and contained mostly Fe, suggesting an iron oxide mineral such as magnetite (Fe3O4). Our data thus provide evidence that secondary Fe(II) and Fe(II)/Fe(III) mixed minerals could be a sink for Cd in soils under reducing conditions, thus decreasing the mobility of Cd in the soil.
authors.affiliation: Geomicrobiology and ‡Environmental Analytical Microscopy, Center for Applied Geosciences, University of Tuebingen , 72076 Tuebingen, Germany.
authors.forename: E Marie
authors.initials: EM
authors.lastname: Muehe
authors.forename: Irini J
authors.initials: IJ
authors.lastname: Adaktylou
authors.forename: Martin
authors.initials: M
authors.lastname: Obst
authors.forename: Fabian
authors.initials: F
authors.lastname: Zeitvogel
authors.forename: Sebastian
authors.initials: S
authors.lastname: Behrens
authors.forename: Britta
authors.initials: B
authors.lastname: Planer-Friedrich
authors.forename: Ute
authors.initials: U
authors.lastname: Kraemer
authors.forename: Andreas
authors.initials: A
authors.lastname: Kappler
mesh_terms: D000085:Acetates / Q000378:metabolism; D001419:Bacteria / Q000235:genetics / Q000378:metabolism*; D002104:Cadmium / Q000737:chemistry*; D002244:Carbon / Q000378:metabolism*; D018628:Gene Dosage; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D007773:Lactates / Q000378:metabolism; D008903:Minerals / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D012329:RNA, Bacterial / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012987:Soil; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000737:chemistry*
chemical_list: D000085:Acetates; D007773:Lactates; D008903:Minerals; D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; D012987:Soil; D012989:Soil Pollutants; D002104:Cadmium; D002244:Carbon; D007501:Iron