Simultaneous release of Fe and As during the reductive dissolution of Pb-As jarosite by Shewanella putrefaciens CN32.

Jarosites are produced during metallurgical processing, on oxidized sulfide deposits, and in acid mine drainage environments. Despite the environmental relevance of jarosites, few studies have examined their biogeochemical stability. This study demonstrates the simultaneous reduction of structural Fe(III) and aqueous As(V) during the dissolution of synthetic Pb-As jarosite (PbFe(3)(SO(4),AsO(4))(2)(OH)(6)) by Shewanella putrefaciens using batch experiments under anaerobic circumneutral conditions. Fe(III) reduction occurred immediately in inoculated samples while As(V) reduction was observed after 72 h. XANES spectra showed As(III) (14.7%) in the solid phase at 168 h coincident with decreased aqueous As(V). At 336 h, XANES spectra and aqueous speciation analysis demonstrated 20.2% and 3.0% of total As was present as As(III) in the solid and aqueous phase, respectively. In contrast, 12.4% of total Fe was present as aqueous Fe(II) and was below the detection limits of XANES in the solid phase. TEM-EDS analysis at 336 h showed secondary precipitates enriched in Fe and O with minor amounts of As and Pb. Based on experimental data and thermodynamic modeling, we suggest that structural Fe(III) reduction was thermodynamically driven while aqueous As(V) reduction was triggered by detoxification induced to offset the high As(V) (328 µM) concentrations released during dissolution.

Reductive dissolution of Tl(I)-jarosite by Shewanella putrefaciens: providing new insights into Tl biogeochemistry.

Thallium (Tl) is emerging as a metal of concern in countries such as China due to its release during the natural weathering of Tl-bearing ore deposits and mining activities. Despite the high toxicity of Tl, few studies have examined the reductive dissolution of Tl mineral phases by microbial populations. In this study we examined the dissolution of synthetic Tl(I)-jarosite, (H(3)O)(0.29)Tl(0.71)Fe(2.74)(SO(4))(2)(OH)(5.22)(H(2)O)(0.78), by Shewanella putrefaciens CN32 using batch experiments under anaerobic circumneutral conditions. Fe(II) concentrations were measured over time and showed Fe(II) production (4.6 mM) in inoculated samples by 893 h not seen in mineral and dead cell controls. Release of aqueous Tl was enhanced in inoculated samples whereby maximum concentrations in inoculated and cell-free samples reached 3.2 and 2.1 mM, respectively, by termination of the experiment. Complementary batch Tl/S. putrefaciens sorption experiments were conducted under experimentally relevant pH (5 and 6.3) at a Tl concentration of 35 µM and did not show significant Tl accumulation by either live or dead cells. Therefore, in contrast to many metals such as Pb and Cd, S. putrefaciens does not represent a sink for Tl in the environment and Tl is readily released from Tl-jarosite during both abiotic and biotic dissolution.

Effects of pH, ionic strength, dissolved organic matter, and flow rate on the co-transport of MS2 bacteriophages with kaolinite in gravel aquifer media.

Viruses are often associated with colloids in wastewater and could be transported with colloids into groundwater from land disposal of human and animal effluent and sludge, causing contamination of groundwater. To investigate the role of colloids in the transport of viruses in groundwater, experiments were conducted using a 2m long column packed with heterogeneous gravel aquifer media. Bacteriophage MS2 was used as the model virus and kaolinite as the model colloid. Experimental data were analyzed using Temporal Moment Analysis and Filtration Theory. In the absence of kaolinite colloid, MS2 phage traveled slightly faster than the conservative tracer bromide (Br), with little differences observed between unfiltered and filtered MS2 phage (0.22 microm as the operational cut-off for colloid-free virus). In the presence of kaolinite colloids, MS2 phage breakthrough occurred concurrently with that of the colloidal particles and the time taken to reach the peak virus concentration was reduced, suggesting a colloid-facilitated virus transport in terms of peak-concentration time and velocity. Meanwhile mass recovery and magnitude of concentrations of the phages were significantly reduced, indicating colloid-assisted virus attenuation in terms of concentrations and mass. Decreasing the pH or increasing the ionic strength increased the level of virus attachment to the aquifer media and colloids, and virus transport became more retarded, resulting in lower peak-concentration, lower mass recovery, longer peak-concentration time, and greater apparent collision efficiency. Increasing the concentration of dissolved organic matter (DOM) or flow rate resulted in faster virus transport velocity, higher peak-concentrations and mass recoveries, and lower apparent collision efficiencies. The dual-role of colloids in transport viruses has important implications for risk analysis and remediation of virus-contaminated sites.