Control of mercury and methylmercury in contaminated sediments using biochars: A long-term microcosm study

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.apgeochem.2018.02.004 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/The effectiveness of activated carbon and four types of biochar, switchgrass (300 °C and 600 °C), poultry manure (600 °C), and oak (∼700 °C) with respect to mercury (Hg) and methylmercury (MeHg) control was assessed in microcosm experiments carried out for 524 d. Early in the study (<30 d), minimal differences in concentrations of <0.45-μm filtered total Hg (THg) in control and 5% biochar-amended systems were observed. At later stages, THg concentrations in the amended systems decreased to 8–80% of concentrations in the sediment controls. Aqueous concentrations of MeHg were generally lower in the amended systems than in the controls, with an initial peak in MeHg concentration corresponding to the onset of iron and sulfate reduction (∼40 d) and a second peak to methanogenic conditions (∼400 d). Pyrosequencing analyses indicate the microbial communities initially associated with fermenters and later shifted to iron-reducing bacteria (FeRB), sulfate-reducing bacteria (SRB), and methanogens. These analyses also indicate the existence of 12 organisms associated with Hg methylation in all systems. Community shifts were correlated with changes in the concentrations of carbon sources (dissolved organic carbon (DOC) and organic acids) and electron acceptors (NO3−, Fe, and SO42−). Co-blending of biochars with Hg-contaminated sediment can be an alternative remediation method for controlling the release of Hg and MeHg, but the potential for Hg methylation under some conditions requires consideration.Natural Sciences and Engineering Research Council of CanadaCanada Research ChairsE. I. du Pont de Nemours and Compan

Microbial processes with the potential to mobilize As from a circumneutral-pH mixture of flotation and roaster tailings

The Northwest Tailings Containment Area at the inactive Giant Mine (Canada) contains a complex mixture of arsenic-containing substances, including flotation tailings (84.8 wt%; with 0.4 wt% residual S), roaster calcine wastes (14.4 wt% Fe oxides), and arsenic trioxide (0.8 wt%) derived from an electrostatic precipitator as well as As-containing water (21.3 ± 4.1 mg L−1 As) derived from the underground mine workings. In the vadose zone the tailings pore water has a pH of 7.6 and contains elevated metal(loid)s (2.37 ± 5.90 mg L−1 As); mineral oxidizers account for 2.5% of total 16S rRNA reads in solid samples. In the underlying saturated tailings, dissolved Fe and As concentrations increase with depth (up to 72 and 20 mg L−1, respectively), and the mean relative abundance of Fe(III)-reducers is 0.54% of total reads. The potential for As mobilization via both reductive and oxidative (bio)processes should be considered in Giant Mine remediation activities. The current remediation plan includes installation of an engineered cover that incorporates a geosynthetic barrier layer

Warm-up phenomenon in myotonia associated with the V445M sodium channel mutation

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Microbiological and geochemical characterization of As-bearing tailings and underlying sediments

Over the past 100 years, extensive oxidation of As-bearing sulfide-rich tailings from the abandoned Long Lake Gold Mine (Canada) has resulted in the formation of acid mine drainage (pH 2.0-3.9) containing high concentrations of dissolved As (∼400 mg L ), SO , Fe and other metals. Dissolved As is predominantly present as As(III), with increased As(V) near the tailings surface. Pore-gas O is depleted to &lt; 1 vol% in the upper 30-80 cm of the tailings profile. The primary sulfides, pyrite and arsenopyrite, are highly oxidized in the upper portions of the tailings. Elevated proportions of sulfide-oxidizing prokaryotes are present in this zone (mean 32.3% of total reads). The tailings are underlain by sediments rich in organic C. Enrichment in δ S-SO in pore-water samples in the organic C-rich zone is consistent with dissimilatory sulfate reduction. Synchrotron-based spectroscopy indicates an abundance of ferric arsenate phases near the impoundment surface and the presence of secondary arsenic sulfides in the organic-C beneath the tailings. The persistence of elevated As concentrations beneath the tailings indicates precipitation of secondary As sulfides is not sufficient to completely remove dissolved As. The oxidation of sulfides and release of As is expected to continue for decades. The findings will inform future remediation efforts and provide a foundation for the long-term monitoring of the effectiveness of the remediation program. [Abstract copyright: Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.