W. Douglas Gould

Microbiological, chemical, and mineralogical characterization of the kidd creek mine tailings impoundment, Timmins area, Ontario

Bacterial enumeration and geochemical characterization were undertaken at three sites on the sulfide‐rich tailings impoundment at the Kidd Creek metallurgical site, Timmins, Ontario, Canada. The three sites were selected to represent varying degrees of sulfide oxidation to assess the changes in water chemistry, in the mineralogical composition of the tailings, and in bacterial populations as the sulfide oxidation process proceeds under natural field conditions. The first site was characterized as having negligible oxidation‐derived alteration, the pH of the porewater varied from 6.5 to 7.5, and the concentrations of dissolved constituents were similar to those observed in the deeper, unaltered tailings. Mineralogical examination of the tailings grains indicated that the sulfide surfaces were sharp and unreplaced. At this site, the predominant sulfur‐oxidizing bacteria were Thiobacillus thioparus and related species. The second site showed evidence of the onset of acidification, the pH of the near‐surface ...

Effect of Immobilization on Kinetic and Thermodynamic Characteristics of Sulfide Oxidase from Arthrobacter Species

Abstract In order to determine the impact of immobilization on biocatalytic efficacy of sulfide oxidase, the kinetic and thermodynamic properties of native and DEAE‐cellulose immobilized sulfide oxidase from Arthrobacter species FR‐3 were evaluated. Immobilization increased the catalytic efficiency of sulfide oxidase by producing a lower Michaelis‐Menten constant (K m ) and a higher rate of catalysis (V max ) at different temperatures. The first‐order kinetic analysis of thermal denaturation demonstrated that the values of enthalpy (ΔH d *) and entropy (ΔS d *) of immobilized sulfide oxidase were lower than the native enzyme, confirming the thermal stabilization of sulfide oxidase by immobilization. The ΔH d * and ΔS d * of the immobilized enzyme at 35°C were 138.07 kJ/mol and 122.04 J/K/mol, respectively. These results suggest that immobilization made the sulfide oxidase from Arthrobacter sp. FR‐3 thermodynamically more efficient for catalysis of sulfide oxidation.

Effect of Electron Donor to Sulfate Ratio on Mercury Methylation in Floodplain Sediments under Saturated Flow Conditions

A column transport experiment was conducted to examine the release and methylation of Hg using Hg contaminated sediment from the floodplain of the South River near Waynesboro, Virginia. Three input solutions were sequentially introduced into the column. Input 1 was unamended South River water, Input 2 was river water amended with 100 mg L−1 SO4 and 3600 mg L−1 lactate, and Input 3 was river water amended with 500 mg L−1 SO4 and 340 mg L−1 lactate. During the first stage of the experiment (Input 1) the effluent Hg concentration was initially 4 µg L−1 and peaked at 21 µg L−1 and after 21 pore volumes stabilized at 13 µg L−1. During the second stage, at high lactate to SO4 ratios, elevated concentrations of acetic and propionic acids were detected, indicating that fermentative bacteria were dominant. During the third stage, at high SO4 to lactate ratios, a decrease in SO4 and an increase in H2S concentrations were detected in the column effluent indicating that SO4 reduction was occurring. Concentrations of methyl Hg (MeHg) in the effluent were variable over the duration of the experiment. During the first phase, concentrations of MeHg remained <3.3 ng L−1. During the fermentative stage, concentrations of MeHg increased to a maximum value of 32 ng L−1, and during the sulfate-reducing stage to a maximum value of 266 ng L−1. When the column was deconstructed both molecular and cultural techniques indicated that sulfate reducing bacteria were most dominant near the influent port. These results indicate that the formation of MeHg in the sediment is not limited by the availability of Hg and that the bacterial community that contributes to mercury methylation can respond quickly to changes in the abundances of electron donors and acceptors.

Role of Organic Carbon Sources and Sulfate in Controlling Net Methylmercury Production in Riverbank Sediments of the South River, VA (USA)

ABSTRACT Mercury (Hg) transport and methylmercury (MeHg) production in riverbank sediments are complex processes influenced by site-specific physical and biogeochemical conditions. The South River watershed in VA, USA, contains elevated concentrations of Hg in riverbank and floodplain sediments, which has the potential to methylate. The role of specific organic carbon sources in promoting methylation reactions in natural sediments under dynamic flow conditions is not well understood. Four saturated column experiments were conducted, including a control column, which received South River water as an influent solution, and three columns that received South River water amended with: acetate (5.8 mM); lactate (5.7 mM); and lactate (5.7 mM) with SO42− (10.1 mM). The amendments were selected to promote growth of different microorganisms to gain an understanding of the microbial processes, controlling rates of methylation. The column receiving lactate and SO42− had the highest MeHg concentrations in the effluent and in the pore water near the effluent at 1.8 and 4.9 μg L−1, respectively. At the cessation of the column experiments, the lactate–sulfate column sediments contained the highest populations of enumerable sulfur-reducing bacteria and the highest solid-phase MeHg at 530 ± 100 ng g−1 dry wt. from the interval closest to the influent. The results suggest that the form and availability of electron donors and acceptors are primary factors controlling rates of methylation in the South River sediment.

Assessing Cellulolysis in Passive Treatment Systems for Mine Drainage: A Modified Enzyme Assay

A modified cellulase enzyme assay was developed to monitor organic matter degradation in passive treatment systems for mine drainage. This fluorogenic substrate method facilitates assessment of exo-(1,4)-β-D-glucanase, endo-(1,4)-β-D-glucanase, and β-glucosidase, which compose an important cellulase enzyme system. The modified method was developed and refined using samples of organic carbon-amended mine tailings from field experiments where sulfate reduction was induced as a strategy for managing water quality. Sample masses (3 g) and the number of replicates ( ≥ 3) were optimized. Matrix interferences within these metal-rich samples were found to be insignificant. Application of this modified cellulase assay method provided insight into the availability and degradation of organic carbon within the amended tailings. Results of this study indicate that cellulase enzyme assays can be applied to passive treatment systems for mine drainage, which commonly contain elevated concentrations of metals.