Gold Mining Effluent Research Articles

Arsenic in subArctic lakes influenced by gold mine effluent: the occurrence of organoarsenicals and ‘hidden’ arsenic

A series of subArctic lakes near Yellowknife, Northwest Territories, Canada, are contaminated with arsenic released from a gold mine. The high environmental arsenic levels afforded an opportunity to identify factors that control methylarsenical production in freshwater sediments. A large variety of methylated arsenicals were observed in most pore water and water column samples from lakes contaminated by aqueous or atmospheric arsenic inputs, albeit at low concentrations relative to inorganic arsenic (generally less than 10% of the total dissolved arsenic concentration). Biologically-mediated methylation/demethylation reactions, therefore, may influence the local arsenic cycle. Water column samples exhibited a consistent methylarsenic composition in which the dominant form was dimethylarsonic acid, followed by monomethylarsinic acid. A much broader range of mono-, di- and trimethylated arsenicals was found in sediment pore water, and the composition of methylarsenic species was highly variable both within and between cores. We provide indirect evidence that many samples contained mono-, di-, and trimethylated arsenic(III)thiols, of the form (CH 3) nAs III(SR) 3−n ( n = 1, 2, 3), the existence of which has been predicted but not previously demonstrated in the environment. The total dissolved methylarsenic concentration in cores consistently exhibited a subsurface maxima between 5 and 15 cm depth, which suggests—in conjunction with the presence of other metabolites in pore water —that methylation may be enhanced by sulfate-reducing bacteria. The role of sulfate-reducers in the production of methylarsenicals observed in sediment pore water is also supported by co-variations with depth between the concentration of methylarsenic species and iron dissolution or other chemical distributions attributed to metabolism by heterotrophic bacteria across different redox zones. Many samples contained appreciable concentrations of arsenicals the specific identity of which are presently unknown, and some of which are ‘hidden’ to conventional hydride-generation analyses. At least one unidentified arsenical found in lake water and sediment pore water appears to have been produced directly or indirectly from atmospheric emissions from the gold mine. The occurrence of methylated arsenicals and hidden arsenic at concentrations that comprise a substantial portion of the total arsenic budget in some aquatic systems suggests that current models of lacustrine arsenic cycling that incorporate only inorganic arsenicals need to be revisited.

Maintenance ofRhodotorula rubra isolated from liquid samples of gold mine effluents

TheRhodotorula rubra strain isolated from waste waters of a gold mining plant has demonstrated the ability to grow in the presence of cyanide. The maintenance of this strain in complex organic media leads to a loss of this ability. To preserve the cyanide resistance ofR. rubra we tested the following maintenance methods: subculturing in sterile distilled water, freezing at −20, −40, −70°C, liquid nitrogen freezing and the paper replica method. The ability to grow in the presence of cyanide was preserved and a higher viability level was observed for cells maintained frozen at −70°C, in liquid nitrogen and by the paper replica method. Preservation in distilled water resulted in the lowest viability after twelve months of storage.

Utilization of ammonia, generated from abiotic cyanide degradation, by Rhodotorula rubra

The viability of the yeast Rhodotorula rubra, isolated from liquid samples of gold-mine effluents, was not affected by the presence of 11.52 mM cyanide. The yeast was able to utilize ammonia, generated from abiotic cyanide degradation in the presence of reducing sugars, in aerobic culture at pH 9.0. These physiological characteristics encourage studies with mixed cultures of cyanide-degrading organisms, using this yeast as an assimilator of ammonia.

Arsenic bioaccumulation and toxicity in aquatic macrophytes exposed to gold-mine effluent: relationships with environmental partitioning, metal uptake and nutrients

Arsenic concentrations in freshwater macrophytes were examined in relation to arsenic loadings in sediments (solid phase and pore water) and surface waters for a group of lakes contaminated by the discharge of mine tailings near Yellowknife, N.W.T. Lakes closest to the current discharge were highly contaminated with arsenic (up to 18 650 μg g −1 in sediments) compared with other areas. Macrophytes tended to bioconcentrate arsenic relative to sediment concentrations (up to a factor of ten), with submerged species containing much higher levels of arsenic than emergents. Differences in levels between the most common submerged ( Potamogeton pectinatus L.) and emergent species ( Typha latifolia L.) were attributed to differences in growth form and possible differences in the ability to exclude arsenic with increasing sediment concentrations. High environmental arsenic concentrations appeared to have negative effects on Typha latifolia, as suggested by decreased stand height, necrosis of leaf tips and reduced micro-nutrient concentrations in root tissues of copper, managanese, and zinc. Phytotoxic symptoms in Typha were generally observed at sediment and water concentrations exceeding 300 μg g −1 and 400 μg l −1, respectively. The lack of relationships between tissue concentrations of arsenic and environmental concentrations of phosphorus (as pore water PO −3 4, particulate total extractable P, or As:P ratios) did not support the hypothesis that arsenic bioavailability (as arsenate) and toxicity is related to its competition for uptake with phosphate.

Arsenic transport in a watershed receiving gold mine effluent near Yellowknife, Northwest Territories, Canada

The presence of abnormally high concentrations of arsenic in sediment and water samples collected from a chain of small lakes afforded a unique opportunity to investigate the environmental partitioning and speciation of inorganic arsenic in fresh water. The distribution of arsenic in water, surface sediment (0–5 cm depth) and associated pore water downstream of the discharge differed from that expected due to conservative dilution and/or sediment adsorption from a point-source. Inorganic arsenic in the water column, sediment particulates and pore water exhibited a maximum concentration ∼ 4–6 km downstream of the gold-mine input. Arsenite (As(III)) was the predominant arsenical in the sediment pore water throughout the watershed, whereas arsenate (As(V)) comprised the vast majority of dissolved arsenic in water column samples. Arsenite was not detected in the mine effluent, but was found in increasing concentrations in the water column with increasing downstream distance from the discharge pipe. There are two possible mechanisms for the downstream redistribution of historical arsenic inputs in this system: (1) bulk movement via sediment/particulate transport; and (2) redissolution from sediments during early diagenesis, followed by upward diffusion and transport to downstream areas. Sediment distributions of other substances which are ‘tracers’ of the gold-mine effluent (e.g. antimony, copper, gold, nickel, zinc, sulphate and chloride ion) were examined in order to distinguish between these mechanisms. Collectively, the data indicate that the arsenic distribution in surficial sediments of the study area is controlled partially by the bulk movement of sediments, followed by burial with less contaminated sediments in the upper reaches of the watershed. Particulate concentrations of arsenic contributed significantly to the total arsenic concentrations in the water column downstream of the gold-mine discharge (up to 70% of total As concentration). The extremely high concentrations of arsenicals in sediment pore water (up to 68.9 μM) and the overlying water column (up to 7.3 μM in dissolved form) in areas further removed from the input, however, are attributable to remobilization from sediments through redox-related dissolution. This release of dissolved arsenic during sediment diagenesis may be enhanced by anthropogenically-enhanced sulfate deposition, also associated with gold-mining activity.

The Photochemical Treatment of Wastewater by Ultraviolet Irradiation of Semiconductors

Abstract The primary photoefficiency of ten semiconductors to produce reactive oxidising species under ultraviolet (UV) illumination has been evaluated. TiO2 in the anatase phase was shown to be at least an order of magnitude more efficient than the other semiconductors so was chosen for further experimentation. While the anatase-UV treatment was shown not to be feasible for secondary effluent disinfection, the process did lead to substantial reduction in the toxicity to algae of PCB containing wastewater. Also, the process reduced the total organic chlorine content of a pulp and paper plant's chlorinated bleach-plant effluent and left lignin model compounds more amenable to biological degradation. In addition, the process destroyed cyanide in synthetic solutions and in gold and base metal mine effluents. Based on studies of model compounds, the reaction mechanisms for the process are discussed. Also, recommendations are made as to future research requirements for optimization of the process and for study of its economic viability.