The mineralogical composition of mine wastes is generally considered to be the most important determinant of mine water geochemistry. However, environmental factors can significantly modify the weathering behavior of these materials, and the failure to consider these factors in experimental work may yield biased results. This is a particularly important consideration for mines in arctic and sub-arctic regions, where environmental conditions are far from those of a typical laboratory. The present study focuses on evaluating the influence of ambient thermal conditions on the weathering of pyrrhotite- and serpentine-rich tailings. To this end, laboratory-scale leached columns were used to simulate weathering of tailings over 544 days either at room-temperature or under freeze-thaw cycles (_ 20 degrees C/+20.5 degrees C). Microbiological analyses performed as part of the initial material characterization were unable to detect microbial communities. Although this result was unexpected and unusual, we found that elemental sulfur, which is stable in the absence of sulfur-oxidizing bacteria, had accumulated in the weathered tailings, representing up to 89-92 % sulfur products from pyrrhotite oxidation. Thiosulfate and sulfate were important oxidation products in leachates under both thermal conditions; however, freeze-thaw cycling appeared to enhance the stability of thiosulfate. The dominance of elemental sulfur and thiosulfate, which are produced via non-acid-generating reactions, suggests that the hydrolysis of Fe3+ and Al3+ may have been comparatively important sources of acid generation. Serpentine dissolution was more extensive at roomtemperature but likely provided little to no alkalinity under freeze-thaw conditions due to slower dissolution kinetics. Calcite and dolomite were the principal buffering phases despite their low abundance. The mobility of Zn seemed to not be limited in either test, whereas Fe and Ni were effectively sequestered via adsorption and/or coprecipitation with ferrihydrite and gibbsite. Under room-temperature conditions, depletion or passivation of the carbonate minerals gave rise to a new buffering regime controlled by gibbsite. Although this maintained the pH around 5.1, aqueous Fe and Ni concentrations spiked (max = 7.6 and 1.5 mM, respectively) as they were released or desorbed from the gibbsite. Leachate pH values remained slightly elevated in the freeze-thaw tests and had not yet stabilized by the end of the experiment; the sequestration of Fe and Ni was not disrupted.

Thawing permafrost releases labile organic carbon and alters groundwater geochemistry and hydrology with uncertain outcomes for the mobility of hazardous metal(loid)s. Managing water quality in thawing permafrost regions is predicated on a detailed understanding of the speciation and abundance of metal(loid)s in permafrost soils and porewaters produced during thaw, which remains limited at present. This study contributes new knowledge on the sources and fate of arsenic during the thaw of organic-rich permafrost using samples collected from a subarctic permafrost region associated with geogenic arsenic (Dawson Range, Yukon, Canada). Several permafrost cores and active-layer samples from this region were analyzed for their solid-phase and aqueous geochemical characteristics and their arsenic speciation. Porewaters were extracted from permafrost cores after thaw under anaerobic conditions for aqueous geochemical analyses. Bedrock samples from the field site were also analyzed for arsenic speciation and mineralogy. X-ray diffraction and X-ray near-edge spectroscopy (XANES) analyses of weathered bedrock upgradient of soil sampling locations contained arsenic(V) hosted in iron-(oxyhydr)oxides and scorodite. XANES and micro X-ray fluorescence analyses of permafrost soils indicated a mixture of arsenic(III) and arsenic(V), indicating redox recycling of arsenic. Soil-bound arsenic was colocated with iron, likely as arseniferous iron-(oxyhydr)oxides that have been encapsulated by aggrading permafrost over geologic time. However, permafrost thaw produced porewater containing elevated dissolved arsenic (median 40 mu g L-1, range 2-96 mu g L-1). Thawed permafrost porewater also contained elevated dissolved iron (median 5.5 mg L-1, range 0.5-40 mg L-1) and dissolved organic carbon (median 423 mg L-1, range 72-3240 mg L-1), indicative of reducing conditions. This study highlights that arsenic can be found in reactive forms in permafrost soil, and that its thaw can release arsenic and iron to porewater and produce poor water quality.

Microorganisms in hypersaline potash mining byproducts and their potential environmental applications have not been extensively reported. This study reports the diverse waste-impacted microbial communities (archaea and bacteria) adapted to extreme salinity (>10-25%). Of these, halotolerant Croceicoccus sp. FTI14 was investigated as a biosorbent for removing dissolved Cu(II) and Cr(VI) from synthetic Cu(II) and Cr(VI)-contaminated DI, groundwater and saline groundwater (0.55 M ionic strength). FTI14 biomass was oven-dried, finely ground, and investigated in batch biosorption experiments. At initial metal concentrations of 40 mg/L, FTI14 removed 40 +/- 0.7% (16.3 +/- 0.5 mg/g) and 19 +/- 0.1% (7.8 +/- 0.1 mg/g) of the Cu(II) from deionized water and saline groundwater, respectively, while only 22.9 +/- 0.7% (9.6 +/- 0.2 mg/g) and 2.1 +/- 0.6% (1.0 +/- 0.3 mg/g) Cr(VI) removal was achieved. Cu(II) uptake (mg/g) exceeded Cr(VI) uptake by a factor of 1.7-7.8. Langmuir and Freundlich models were applied on FTI14 biosorption isotherm data. The Freundlich model showed a better fit for both Cu(II) and Cr(VI), as indicated by the AIC values compared with evidence ratios. Synchrotron- based scanning transmission X-ray microscopy (STXM) visualizations of the biosorbent showed a mixture of whole cells and indistinct biomass and a spatial association between metals and biomass. Metal exposure alters the amide functional groups peak in Fourier transform Infra-red (FTIR) spectra, suggesting its role in sorption process. Thus, this study indicates culturable halotolerant microorganisms from hypersaline potash mining byproducts and its potential as biosorbent applications for metal removal from impacted groundwater.

Kinetic leached columns (KLCs) were used to simulate the weathering of pyrrhotite-rich tailings from Raglan Mine (QC, Canada) and evaluate the effects of freeze-thaw cycles and salinity on long-term trends in sulfide oxidation. This study focuses on the results of a series of oxygen consumption tests (OCTs) with additional observations from the dismantlement of the KLCs. Four treatments were evaluated in duplicate in the KLCs: (1) room-temperature and deionized water; (2) room-temperature and saline water; (3) freeze-thaw cycles and deionized water; and (4) freeze-thaw cycles and saline water. Oxygen fluxes showed no reproducible differences over the course of the study when comparing between deionized and saline water columns within each thermal regime. However, fluxes may have differed slightly at several timepoints. The room-temperature and freeze-thaw columns displayed somewhat different oxidative behaviors. Notably, all columns stabilized at similar oxygen fluxes, though the amount of time until stability differed for the two thermal regimes. Visual observations made upon dismantlement of the columns revealed extensive oxidation and cementation throughout the entire depth of the columns with no significant differences noted between the room-temperature and freeze-thaw columns. This study provides novel insights into the long-term evolution of sulfide oxidation in mine tailings weathering under conditions relevant to northern mine sites.

Hair has long been explored as a potential biomarker of lead exposure since lead is readily adsorbed into hair's keratinous matrix; however, the utility of hair as a biomarker for lead exposure is hampered by its susceptibility to external contamination: lead particles attach to the exposed hair surface, confounding estimates of endogenous concentrations. This study describes the development of a hair screening tool, in which the confounding influence of external contamination are mitigated by focusing on the unexposed hair root, to predict elevated blood lead levels (BLLs). This tool requires a single strand of scalp hair, which is analyzed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Forty-four (44) workers with high potential for lead exposure, and 63 reference individuals (with no known lead exposure) volunteered for the study. Hair lead level (HLL) thresholds were developed using methods from clinical assessment to screen exceedances of BLL thresholds at 10 and 15 mu g/dL. Hair from both groups showed significantly lower lead concentrations in below-scalp portions compared to above the scalp (above-scalp was 11.2 times higher in workers, and 3.7 times higher in reference group). Hair lead concentrations below the scalp in workers significantly predicted BLLs. HLL thresholds for screening BLLs were 0.60 mg/kg and 0.75 mg/kg for BLLs of 10 mu g/dL and 15 mu g/dL, respectively. These HLL thresholds yielded high sensitivity (>85%), and slightly lower specificity (67% and 33%, for BLL thresholds of 10 mu g/dL and 15 mu g/dL, respectively). This study provides reference HLLs in non-contaminated portions of hair (<0.097 mg/kg), shows the significance of external contamination on exposed portions of hair even in a reference population, and assesses the effectiveness of below-scalp hair as a biomarker of elevated lead exposure. This hair screening tool effectively predicted BLL exceedances and could be considered as a noninvasive alternative to blood sampling.

Historical mining and mineral processing at the former Giant Mine (Yellowknife, NT, Canada) created an enduring legacy of arsenic (As) and antimony (Sb) contamination. Approximately 237,000 tonnes of arsenic trioxide roaster waste (ATRW) generated between 1948 and 1999 remains stored on-site in underground chambers. We studied the chemical forms and phase associations of As and Sb to improve understanding of ATRW environmental behavior. Although arsenolite [As2O3] is the principal As and Sb host, we also observed minor associations of As with Fe oxides. Arsenic K-edge X-ray absorption spectroscopy (XAS) revealed As(III) dominated ATRW, with some As(V) and As(-I) also present. Arsenic coordination and bonding is consistent with arsenolite, while scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) showed minor As association with Fe oxides and arsenopyrite [FeAsS]. Antimony K-edge XAS revealed variable proportions of Sb(III) and Sb(V), with Sb-O, Sb-Sb and Sb-As bonding consistent with stibioclaudetite [AsSbO3] or Sb-substituted arsenolite. Electron microprobe analysis (EMPA) results showed variable but quantitative Sb substitution for As in arsenolite grains, possibly influencing ATRW solubility and reactivity under environmental conditions. Overall, our results reveal complex As and Sb phase associations with important implications for ongoing remediation efforts and long-term environmental fate of ATRW solids.

High-energy-resolution fluorescence-detected (HERFD) X-ray absorption near-edge spectroscopy (XANES) is a spectroscopic method that allows for increased spectral feature resolution, and greater selectivity to decrease complex matrix effects compared with conventional XANES. XANES is an ideal tool for speciation of elements in solid-phase environmental samples. Accurate speciation of As in mine waste materials is important for understanding the mobility and toxicity of As in near-surface environments. In this study, linear combination fitting (LCF) was performed on synthetic spectra generated from mixtures of eight measured reference compounds for both HERFD-XANES and transmission-detected XANES to evaluate the improvement in quantitative speciation with HERFD-XANES spectra. The reference compounds arsenolite (As2O3), orpiment (As2S3), getchellite (AsSbS3), arsenopyrite (FeAsS), kaňkite (FeAsO4·3.5H2O), scorodite (FeAsO4·2H2O), sodium arsenate (Na3AsO4), and realgar (As4S4) were selected for their importance in mine waste systems. Statistical methods of principal component analysis and target transformation were employed to determine whether HERFD improves identification of the components in a dataset of mixtures of reference compounds. LCF was performed on HERFD- and total fluorescence yield (TFY)-XANES spectra collected from mine waste samples. Arsenopyrite, arsenolite, orpiment, and sodium arsenate were more accurately identified in the synthetic HERFD-XANES spectra compared with the transmission-XANES spectra. In mine waste samples containing arsenopyrite and either scorodite or kaňkite, LCF with HERFD-XANES measurements resulted in fits with smaller R-factors than concurrently collected TFY measurements. The improved accuracy of HERFD-XANES analysis may provide enhanced delineation of As phases controlling biogeochemical reactions in mine wastes, contaminated soils, and remediation systems.

Microbially mediated sulfate reduction is a promising cost-effective and sustainable process utilized in permeable reactive barriers (PRB) and constructed wetlands to treat mine wastewater. Laboratory batch experiments were performed to evaluate nickel (Ni) isotope fractionation associated with precipitation of Ni-sulfides in the presence of the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricansT (DSM-642). Precipitates were collected anaerobically and characterized by synchrotron powder X-ray diffraction (PXRD), scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS), and transmission electron microscopy (TEM). Solid-phase analyses showed that the precipitates associated with bacteria attached to the serum bottle walls were characterized by enhanced size and crystallinity. Lighter Ni isotopes were preferentially concentrated in the solid phase, whereas the solution was enriched in heavier Ni isotopes compared to the input solution. This fractionation pattern was consistent with closed-system equilibrium isotope fractionation, yielding a fractionation factor of Δ60Nisolid-aq = -1.99‰. The Ni isotope fractionation measured in this study indicates multiple Ni reaction mechanisms occurring in the complex SRB-Ni system. The results from this study offer insights into Ni isotope fractionation during interaction with SRB and provide a foundation for the characterization and development of Ni stable isotopes as tracers in environmental applications.

Uranium (U) contamination in groundwater from geogenic sources affects water quality globally. Here, we use a multifaceted isotopic and geochemical approach to elucidate U sources and controls on geogenic U release to groundwater and surface water at a prospective subarctic gold deposit in Yukon, Canada, that is characterized by permafrost, fractured bedrock, and cold (<2 degrees C) groundwater. X-ray absorption spectroscopy, sequential extractions, and micro X-ray fluorescence mapping show extensive subsurface oxidation and solid-phase U present in its hexavalent and mobile form. Limited U-238/U-2(35) isotope fractionation and predominance of U(VI) in rocks suggest U(VI) sorption-desorption is the main driver of U mobilization. Groundwater U concentrations are appreciable (median 38 mu g/L, range 1.2-535 mu g/L) and are explained by high-alkalinity, Ca-rich groundwater produced from oxidative weathering of sulfide and carbonate-mineralized structures around the deposit. Minor U-238/U-2(35) isotope fractionation in groundwater indicates that limited U(VI) reduction occurs beneath permafrost despite groundwater redox conditions below Fe(III) and S(VI) reduction, and groundwater ages inferred from H-3 and C-14 to be on the order of thousands of years. The complexation of U as uranyl-calcium-carbonate complexes and the resilience of these complexes to U(VI) reduction contributes to high U(VI) mobility under cold groundwater conditions. This study provides insight into processes and time scales of U transport in subarctic groundwater at a pivotal time when hydrogeochemical changes may be anticipated in cold regions worldwide due to permafrost degradation.

This study investigated relationships between microbial communities, groundwater chemistry, and geochemical and mineralogical characteristics in field-aged biofilter media from a two-stage, pilot-scale, flow-through biofiltration unit designed to remove Fe(II) and Mn(II) from cold groundwater (8 to 15 °C). High-throughput 16S rRNA gene amplicon sequencing of influent groundwater and biofilter samples (solids, effluents, and backwash water) revealed significant differences in the groundwater, Fe filter, and Mn filter communities. These community differences reflect conditions in each filter that select for populations that biologically oxidize Fe(II) and Mn(II) in the two filters, respectively. Genera identified in both filters included relatives of known Fe(II)-oxidizing bacteria (FeOB), Mn(II)-oxidizing bacteria (MnOB), and ammonia-oxidizing bacteria (AOB). Relatives of AOB and nitrite-oxidizing bacteria were abundant in sequencing reads from both filters. Relatives of FeOB in class Betaproteobacteria dominated the Fe filter. Taxa related to Mn-oxidizing organisms were minor members of the Mn-filter communities; intriguingly, while Alphaproteobacteria dominated (40 ± 10% of sequencing reads) the Mn filter community, these Alphaproteobacteria did not classify as known MnOB. Isolates from Fe and Mn filter backwash enrichment studies provide insight on the identity of MnOB in this system. Novel putative MnOB isolates included Azospirillum sp. CDMB, Solimonas soli CDMK, and Paenibacillus sp. CDME. The isolate Hydrogenophaga strain CDMN can oxidize Mn(II) at 8 °C; this known FeOB is likely capable of Mn(II) oxidation in this system. Synchrotron-based X-ray near-edge spectroscopy (XANES) coupled with electron paramagnetic resonance (EPR) revealed the dominant Mn-oxide that formed was biogenic birnessite. Co-existence of amorphous and crystallized Mn-oxide surface morphologies on the Mn-filter media suggest occurrence of both biological and autocatalytic Mn(II) oxidation in the biofilter. This study provides evidence that biofiltration is a viable approach to remove iron, manganese, and ammonia in cold groundwater systems, and that mineralogical and microbiological approaches can be used to monitor biofiltration system efficacy and function.

We investigated geochemical processes controlling uranium release in neutral-pH (pH ≥ 6) rock drainage (NRD) at a prospective gold deposit hosted in granite, schist, and gneiss. Although uranium is not an economic target at this deposit, it is present in the host rock at a median abundance of 3.7 µg/g, i.e., above the average uranium content of the Earth’s crust. Field bin and column waste-rock weathering experiments using gneiss and schist mine waste rock produced circumneutral-pH (7.6 to 8.4) and high-alkalinity (41 to 499 mg/L as CaCO3) drainage, while granite produced drainage with lower pH (pH 4.7 to >8) and lower alkalinity (<10 to 210 mg/L as CaCO3). In all instances, U release was associated with calcium release and formation of weakly sorbing calcium-carbonato-uranyl aqueous complexes. This process accounted for the higher release of uranium from carbonate-bearing gneiss and schist than from granite despite the latter’s higher solid-phase uranium content. In addition, unweathered carbonate-bearing rocks having a higher sulfide-mineral content released more uranium than their oxidized counterparts because sulfuric acid produced during sulfide-mineral oxidation promoted dissolution of carbonate minerals, release of calcium, and formation of calcium-carbonato-uranyl aqueous complexes. Substantial uranium attenuation occurred during a sequencing experiment involving application of uranium-rich gneiss drainage into columns containing Fe-oxide rich schist. Geochemical modeling indicated that uranium attenuation in the sequencing experiment could be explained through surface complexation and that this process is highly sensitive to dissolved calcium concentrations and pCO2 under NRD conditions.

Anthropogenically-impacted environments offer the opportunity to discover novel microbial species and metabolisms, which may be undetectable in natural systems. Here, a combined metagenomic and geochemical study in Base Mine Lake, Alberta, Canada, which is the only oil sands end pit lake to date, revealed that nitrification was performed by members from Nitrosomonadaceae, Chloroflexi and unclassified Gammaproteobacteria "MBAE14." While Nitrosomonadaceae and Chloroflexi groups were relatively abundant in the upper oxygenated zones, MBAE14 dominated the hypoxic hypolimnetic zones (approximately 30% of total microbial communities); MBAE14 was not detected in the underlying anoxic tailings. Replication rate analyses indicate that MBAE14 grew in metalimnetic and hypolimnetic water cap regions, most actively at the metalimnetic, ammonia/oxygen transition zone consistent with it putatively conducting nitrification. Detailed genomic analyses of MBAE14 evidenced both ammonia oxidation and denitrification into dinitrogen capabilities. However, the absence of known CO2-fixation genes suggests a heterotrophic denitrifying metabolism. Functional marker genes of ammonia oxidation (amo and hao) in the MBAE14 genome are homologous with those conserved in autotrophic nitrifiers, but not with those of known heterotrophic nitrifiers. We propose that this novel MBAE14 inhabits the specific ammonia-rich, oxygen and labile organic matter-limited conditions occurring in Base Mine Lake which selectively favors mixotrophic coupled nitrifier denitrification metabolism. Our results highlight the opportunities to better constrain biogeochemical cycles from the application of metagenomics to engineered systems associated with extractive resource sectors.

The Franklin Expedition (1845–1848) left in search of the Northwest Passage and ended tragically with the loss of all crew members. Mystery surrounds their ultimate fate, with particular speculation around the role of lead poisoning. Our unique study turns nails from crew member John Hartnell into a time machine to determine what happened to the Franklin Expedition crew members. Using micro-X-ray fluorescence mapping, stable isotopic measurements, and laser ablation inductively coupled plasma mass spectrometry, we navigate through the nails and temporally characterize lead, copper and zinc content in our subject during the early expedition. By circumventing external contamination on exposed nail surfaces, we challenge the theory that crew members were exposed to high levels of lead on the expedition. Our analyses suggest that lead exposure actually decreased over the course of the expedition and Hartnell's levels were within a healthy, normal range. Our study also finds, however, that Hartnell was severely zinc-deficient, possibly leading to immuno-suppression and ultimately, tuberculosis and death. The significant weight loss from his illness resulted in a flush of previously stored lead from his bones into his blood (and nail), but only in the last few weeks of life. These findings provide new insight on the fate of the other crew members, including the role that diet and zinc deficiency played in the lives of stranded crew members before their demise.