Microbial Arsenic Release from Historic Gold Mine Tailings, Nova Scotia, Canada

Abstract

The oxidation state of arsenic is an important consideration in the remediation planning for arsenic contaminated tailings, frequently associated with gold mines. As(III) is more toxic and mobile than As(V) and arsenate can be reduced by bacteria. This study focuses on the microbial arsenic release from two abandoned Nova Scotia tailings sites. DNA fragment analysis showed that the microbial ecology varied across the two compositionally diverse sites. Microbial diversity was related to the concentrations of arsenic and iron, which implies the presence of metal reducing bacteria. Known metal reducers belonging to the Geobacter and Schewanella families were identified through gene cloning. Anaerobic microcosms quantified the activity of these bacteria. High calcium tailings showed the most arsenic release, while hardpan areas showed dramatic iron reduction. The presence of reducing bacteria can therefore affect remediation planning, since the use of tailings covers or liming techniques could increase the activity and diversity of metal reducing bacteria.