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Characterization of arsenic species in microbial mats from an inactive gold mine

Geochemistry: Exploration, Environment, Analysis

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Abstract

Filamentous cyanobacterial mats and Fe oxyhydroxide-rich bacterial mats collected near an inactive gold mine in California are enriched in arsenic (As) approximately 1000-fold relative to the waters in contact with them. The predominant organism in the cyanobacterial mat could not be identified using morphological characteristics, but the unique morphology of the sheath-forming ?? protobacterium Leptothrix ochracea was used to identify this species in Fe oxyhydroxide mat samples from several sites near the gold mine. Leptothrix sheaths commonly exceed 10 ??m in length and have an average diameter of 1 ??m. The Fe-oxyhydroxide mats are dominated by L. ochracea sheaths, but use of fluorescently tagged genetic stains reveals the presence of sheathless bacteria that presumably also promote the formation of Fe oxyhydroxide. X-ray absorption fine structure (XAFS) spectroscopy was used to identify As species in these microbial mats. Mat-associated As is predominantly As(V), even when As(III) is the primary dissolved species in contact with the mats. The species of As(V) associated with the cyanobacterial mat could not be conclusively identified; however, it is not associated with Fe oxyhydroxide or other minerals, based on comparison to XAFS spectra of As adsorbed to various substrates. In addition, the cyanobacterial mat XAFS spectrum is different from that of aqueous As(V), suggesting that As(V) in the mat lacks some or all of the coordinating water molecules present in aqueous solution. We hypothesize that As is associated with the exopolysaccharide (EPS) matrix secreted by the cyanobacteria. In Leptothrix-dominated Fe-oxyhydroxide bacterial mats, XAFS analysis clearly indicates that As(V) is associated with the Fe oxyhydroxide as an adsorbed and/or coprecipitated complex.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Characterization of arsenic species in microbial mats from an inactive gold mine
Series title:
Geochemistry: Exploration, Environment, Analysis
Volume
2
Issue:
3
Year Published:
2002
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geochemistry: Exploration, Environment, Analysis
First page:
253
Last page:
261
Number of Pages:
9