Dataset Information

The influence of sulfur and iron on dissolved arsenic concentrations in the shallow subsurface under changing redox conditions.

ABSTRACT: The chemical speciation of arsenic in sediments and porewaters of aquifers is the critical factor that determines whether dissolved arsenic accumulates to potentially toxic levels. Sequestration of arsenic in solid phases, which may occur by adsorption or precipitation processes, controls dissolved concentrations. We present synchrotron x-ray absorption spectra of arsenic in shallow aquifer sediments that indicate the local structure of realgar (AsS) as the primary arsenic-bearing phase in sulfate-reducing conditions at concentrations of 1-3 mmol.kg(-1), which has not previously been verified in sediments at low temperature. Spectroscopic evidence shows that arsenic does not substitute for iron or sulfur in iron sulfide minerals at the molecular scale. A general geochemical model derived from our field and spectroscopic observations show that the ratio of reactive iron to sulfur in the system controls the distribution of solid phases capable of removing arsenic from solution when conditions change from oxidized to reduced, the rate of which is influenced by microbial processes. Because of the difference in solubility of iron versus arsenic sulfides, precipitation of iron sulfide may remove sulfide from solution but not arsenic if precipitation rates are fast. The lack of incorporation of arsenic into iron sulfides may result in the accumulation of dissolved As(III) if adsorption is weak or inhibited. Aquifers particularly at risk for such geochemical conditions are those in which oxidized and reduced waters mix, and where the amount of sulfate available for microbial reduction is limited.

SUBMITTER: O'Day PA

PROVIDER: S-EPMC518762 | biostudies-literature | 2004 Sep

REPOSITORIES: biostudies-literature

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The influence of sulfur and iron on dissolved arsenic concentrations in the shallow subsurface under changing redox conditions.

O'Day Peggy A PA Vlassopoulos Dimitri D Root Robert R Rivera Nelson N

Proceedings of the National Academy of Sciences of the United States of America 20040908 38

The chemical speciation of arsenic in sediments and porewaters of aquifers is the critical factor that determines whether dissolved arsenic accumulates to potentially toxic levels. Sequestration of arsenic in solid phases, which may occur by adsorption or precipitation processes, controls dissolved concentrations. We present synchrotron x-ray absorption spectra of arsenic in shallow aquifer sediments that indicate the local structure of realgar (AsS) as the primary arsenic-bearing phase in sulfa ...[more]

PMID: 15356340

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Project description:The Atlantis Massif rises 4,000 m above the seafloor near the Mid-Atlantic Ridge and consists of rocks uplifted from Earth's lower crust and upper mantle. Exposure of the mantle rocks to seawater leads to their alteration into serpentinites. These aqueous geochemical reactions, collectively known as the process of serpentinization, are exothermic and are associated with the release of hydrogen gas (H2), methane (CH4), and small organic molecules. The biological consequences of this flux of energy and organic compounds from the Atlantis Massif were explored by International Ocean Discovery Program (IODP) Expedition 357, which used seabed drills to collect continuous sequences of shallow (<16 m below seafloor) marine serpentinites and mafic assemblages. Here, we report the census of microbial diversity in samples of the drill cores, as measured by environmental 16S rRNA gene amplicon sequencing. The problem of contamination of subsurface samples was a primary concern during all stages of this project, starting from the initial study design, continuing to the collection of samples from the seafloor, handling the samples shipboard and in the lab, preparing the samples for DNA extraction, and analyzing the DNA sequence data. To distinguish endemic microbial taxa of serpentinite subsurface rocks from seawater residents and other potential contaminants, the distributions of individual 16S rRNA gene sequences among all samples were evaluated, taking into consideration both presence/absence and relative abundances. Our results highlight a few candidate residents of the shallow serpentinite subsurface, including uncultured representatives of the Thermoplasmata, Acidobacteria, Acidimicrobia, and ChloroflexiIMPORTANCE The International Ocean Discovery Program Expedition 357-"Serpentinization and Life"-utilized seabed drills to collect rocks from the oceanic crust. The recovered rock cores represent the shallow serpentinite subsurface of the Atlantis Massif, where reactions between uplifted mantle rocks and water, collectively known as serpentinization, produce environmental conditions that can stimulate biological activity and are thought to be analogous to environments that were prevalent on the early Earth and perhaps other planets. The methodology and results of this project have implications for life detection experiments, including sample return missions, and provide a window into the diversity of microbial communities inhabiting subseafloor serpentinites.

Dataset Information

The influence of sulfur and iron on dissolved arsenic concentrations in the shallow subsurface under changing redox conditions.

Publications

The influence of sulfur and iron on dissolved arsenic concentrations in the shallow subsurface under changing redox conditions.

Similar Datasets

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