Research article

Microbial sulfate reduction and metal attenuation in pH 4 acid mine water

Clinton D Church^1,2 , Richard T Wilkin³ , Charles N Alpers⁴ , Robert O Rye⁵ and R Blaine McCleskey⁶

¹U.S. Geological Survey, California Water Science Center, 4165 Spruance Road, San Diego, CA 92101, USA

²U.S. Department of Agriculture, Agricultural Research Service, Curtin Road, Building 3702, University Park, PA 16802, USA

³U.S. Environmental Protection Agency, National Risk Management Research Laboratory, 919 Kerr Research Drive, Ada, OK 74820, USA

⁴U.S. Geological Survey, California Water Science Center, 6000 J Street, Sacramento, CA 95819, USA

⁵U.S. Geological Survey, Denver Federal Center, Mailstop 963, Denver, CO 80225, USA

⁶U.S. Geological Survey, Suite 127, 3215 Marine Street, Boulder, CO 80303, USA

author email corresponding author email

Geochemical Transactions 2007, 8:10doi:10.1186/1467-4866-8-10

Published:	23 October 2007

Abstract

Sediments recovered from the flooded mine workings of the Penn Mine, a Cu-Zn mine abandoned since the early 1960s, were cultured for anaerobic bacteria over a range of pH (4.0 to 7.5). The molecular biology of sediments and cultures was studied to determine whether sulfate-reducing bacteria (SRB) were active in moderately acidic conditions present in the underground mine workings. Here we document multiple, independent analyses and show evidence that sulfate reduction and associated metal attenuation are occurring in the pH-4 mine environment. Water-chemistry analyses of the mine water reveal: (1) preferential complexation and precipitation by H₂S of Cu and Cd, relative to Zn; (2) stable isotope ratios of ³⁴S/³²S and ¹⁸O/¹⁶O in dissolved SO₄ that are 2–3 ‰ heavier in the mine water, relative to those in surface waters; (3) reduction/oxidation conditions and dissolved gas concentrations consistent with conditions to support anaerobic processes such as sulfate reduction. Scanning electron microscope (SEM) analyses of sediment show 1.5-micrometer, spherical ZnS precipitates. Phospholipid fatty acid (PLFA) and denaturing gradient gel electrophoresis (DGGE) analyses of Penn Mine sediment show a high biomass level with a moderately diverse community structure composed primarily of iron- and sulfate-reducing bacteria. Cultures of sediment from the mine produced dissolved sulfide at pH values near 7 and near 4, forming precipitates of either iron sulfide or elemental sulfur. DGGE coupled with sequence and phylogenetic analysis of 16S rDNA gene segments showed populations of Desulfosporosinus and Desulfitobacterium in Penn Mine sediment and laboratory cultures.