HR: 14:55h
AN: B13F-05    [Abstracts]
TI: Bacterial Influence on the Solubility of Cinnabar and Metacinnabar at New Idria, CA
AU: * Jew, A D
EM: adamjew@stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, 367 Panama St. Green Earth Sciences, Stanford, CA 94305-2115, United States
AU: Rytuba, J J
EM: jrytuba@usgs.gov
AF: United States Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, United States
AU: Spormann, A M
EM: spormann@stanford.edu
AF: Department of Civil & Environmental Engineering, Stanford University, Clark Center E-250, 318 Campus Drive, Stanford, CA 94305-4020, United States
AU: Brown, G E
EM: gordon@pangea.stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, 367 Panama St. Green Earth Sciences, Stanford, CA 94305-2115, United States
AU: Brown, G E
EM: gordon@pangea.stanford.edu
AF: Stanford Synchrotron Radiation Laboratory, 2545 Sand Hill Road, MS 69, Menlo Park, CA 94025, United States
AB: Mercury in the forms of cinnabar (α-HgS) and metacinnabar (β-HgS) is generally considered to be unreactive and of little environmental concern. To determine if this current belief is valid, a consortium of bacteria (including a Thiomonas intermedia-like bacterium) was taken from the acid mine drainage (AMD) pond at the New Idria Hg Mine, San Benito Co., CA, and inoculated into filter-sterilized AMD pond water (pH = 4) containing either ground cinnabar or metacinnabar crystals (<45 μm in diameter), with sampling occurring every 3 days. Under aerobic conditions the samples showed a pronounced increase in aqueous Hg concentration over background water concentrations (350(±20)ng/L). Bacteria growing on α-HgS increased the Hg concentration to 597(±10)μg/L, while bacteria growing on β-HgS resulted in levels of 8.0(±0.2)mg/L; both maxima occurred after 18 days of incubation. Experiments conducted with (1) α- HgS or β-HgS in the presence of killed bacteria (anaerobic), (2) α-HgS with pond water (abiotic), and (3) β-HgS with AMD pond water (abiotic) showed drops in aqueous Hg to below the detection limit (0.1ng/L) within 12 days. Anaerobic growth of the bacterial consortium showed a pattern similar to those of the abiotic water-HgS experiments, except that Hg levels dropped below detection limit within 6 days. These combined results suggest that HgS degradation by this bacterial consortium is an aerobic process. Killed bacteria incubated aerobically showed a slight increase in Hg levels over background water levels (<10x increase) then dropped below detection limit. This observation suggests that enzymes might be involved in the dissolution of HgS and were still viable for ~6 days after sterilization. In aerobic living incubations, the activities of different mercury and sulfide species were estimated using the thermodynamic modeling program Minteq with AMD pond water chemistry determined by ICP-MS and total mercury and total sulfide analyses. These calculations give an equilibrium solubility product for the dissolution of HgS up to 25 orders of magnitude higher than HgS under standard conditions. When compared to calculations by Paquette et al., 1997 and Benoit et al., 1999, the bacterial consortium at New Idria causes an increase in the pK for all reported reactions including H⁺, HS^-, and H₂S of 11-13 orders of magnitude. These results indicate that the biofilm consortium at the New Idria AMD pond has a profound effect on the solubility of cinnabar and metacinnabar, suggesting that a reassessment of HgS stability in aerobic AMD environments is needed.
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0448 Geomicrobiology
DE: 0463 Microbe/mineral interactions
DE: 0489 Trace element cycling (4875)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting