Abstract
Jarosite minerals (AB3(TO4)2(OH)6) are iron hydroxysulfate minerals that can readily incorporate trace metals into their mineral structure. A range of metals can be incorporated into the jarosite structure, including oxyanions such as selenate (SeO42−). Selenium is a micronutrient, but is toxic in relatively low doses. Selenium is present in aqueous systems in its two oxyanion forms: selenate and selenite (SeO32−). The tetrahedral sulfate coordination site can be completely substituted for selenate in jarosite minerals (NaFe3(SO4)x(SeO4)2-x(OH)6). Bacteria have been observed to reduce Se oxyanions to both more reduced forms and insoluble elemental Se. This is a pathway for selenium immobilization at contaminated sites. This experiment investigates the reductive dissolution of two Se-jarosites (solid substitution containing high and low selenium concentrations) in the presence of Shewanella putrefaciens CN32. It was observed that both Fe(III) and selenate were metabolically reduced and released into solution through jarosite dissolution . Selenate was also found to be incorporated intracellularly and reduced to particulate Se which was released upon cell lysis. Compared to the abiotic samples, enhanced dissolution was found with both the live and dead bacteria treatments.
Highlights
Soils and sediments serve as an important interface between the biosphere and hydrosphere and can represent a potential sink for metals [1]
These results indicate that the presence of metabolically active bacteria will stimulate Se-jarosite dissolution under reducing conditions through both metabolic activity and non-metabolic interactions between the dead cells and jarosite minerals
In the presence of live bacteria, Se jarosite dissolution is driven by biological activity, through both metabolic and non-metabolic pathways
Summary
Soils and sediments serve as an important interface between the biosphere and hydrosphere and can represent a potential sink for metals [1]. There have been few prior studies which focus on solid substitution of jarosite minerals in natural environments This is a concern since the potential for metal(loid) ions to be released and remobilized poses an environmental health risk. Selenate and selenite can be microbially reduced to elemental selenium (Se0) and thereby effectively removed from solution [23,24,25,26,27] Several bacteria, such as Enterobacter cloacea, Desulfomicrobium norvegicum, Pseudomonas spp., Rhodospirillum rubrum, Shewanella oneidensis, Thauera selenatis and Bacillus spp., isolated from environments both with and without Se contamination, have been shown to be able to reduce Se metabolically [25,28,29,30,31,32,33]. This study will investigate the reductive dissolution of jarosite as a function of Se phase substitution (high and low percentage of Se-substitution) in the presence of bacteria through quantitative chemical analyses and the comparison of live and dead biomass treatments and abiotic controls
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