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Applied Geochemistry (v.26, #11)

Sources, Transport and Fate of Trace and Toxic Elements in the Environment – IAGS 2009 by Sarah K. Fortner; LeeAnn Munk (pp. 1775-1776).

Hydrogeochemical processes governing the origin, transport and fate of major and trace elements from mine wastes and mineralized rock to surface waters by D. Kirk Nordstrom (pp. 1777-1791).

► Hydrogeochemistry of mines and mineralized areas is complex. ► Mass balances and saturation indices add insight and organization to acid rock drainage data. ► Large database confirms geochemical generalizations for behavior of iron and aluminum.The formation of acid mine drainage from metals extraction or natural acid rock drainage and its mixing with surface waters is a complex process that depends on petrology and mineralogy, structural geology, geomorphology, surface-water hydrology, hydrogeology, climatology, microbiology, chemistry, and mining and mineral processing history. The concentrations of metals, metalloids, acidity, alkalinity, Cl⁻, F⁻ andSO42- found in receiving streams, rivers, and lakes are affected by all of these factors and their interactions. Remediation of mine sites is an engineering concern but to design a remediation plan without understanding the hydrogeochemical processes of contaminant mobilization can lead to ineffective and excessively costly remediation. Furthermore, remediation needs a goal commensurate with natural background conditions rather than water-quality standards that might bear little relation to conditions of a highly mineralized terrain. This paper reviews hydrogeochemical generalizations, primarily from US Geological Survey research, that enhance our understanding of the origin, transport, and fate of contaminants released from mined and mineralized areas.Mobility of potential or actual contaminants from mining and mineral processing activities depends on (1) occurrence: is the mineral source of the contaminant actually present? (2) abundance: is the mineral present in sufficient quantity to make a difference? (3) reactivity: what are the energetics, rates, and mechanisms of sorption and mineral dissolution and precipitation relative to the flow rate of the water? and (4) hydrology: what are the main flow paths for contaminated water? Estimates of relative proportions of minerals dissolved and precipitated can be made with mass-balance calculations if minerals and water compositions along a flow path are known. Combined with discharge, these mass-balance estimates quantify the actual weathering rate of pyrite mineralization in the environment and compare reasonably well with laboratory rates of pyrite oxidation except when large quantities of soluble salts and evaporated mine waters have accumulated underground. Quantitative mineralogy with trace-element compositions can substantially improve the identification of source minerals for specific trace elements through mass balances. Post-dissolution sorption and precipitation (attenuation) reactions depend on the chemical behavior of each element, solution composition and pH, aqueous speciation, temperature, and contact-time with mineral surfaces. For example, little metal attenuation occurs in waters of low pH (<3.5) and metals tend to maintain element ratios indicative of the main mineral or group of minerals from which they dissolved, except Fe, SiO₂, and redox-sensitive oxyanions (As, Sb, Se, Mo, Cr, V). Once dissolved, metal and metalloid concentrations are strongly affected by redox conditions and pH. Iron is the most reactive because it is rapidly oxidized by bacteria and archaea and Fe(III) hydrolyzes and precipitates at low pH (1–3) which is related directly to its first hydrolysis constant, pK₁=2.2. Several insoluble sulfate minerals precipitate at low pH including anglesite, barite, jarosite, alunite and basaluminite. Aluminum hydrolyzes near pH 5 (pK₁=5.0) and provides buffering and removal of Al by mineral precipitation from pH 4–5.5. Dissolved sulfate behaves conservatively because the amount removed from solution by precipitation is usually too small relative to the high concentrations in the water column and relative to the flow rate of the water.

Elevated stream trace and minor element concentrations in the foreland of receding tropical glaciers by Sarah K. Fortner; Bryan G. Mark; Jeffrey M. McKenzie; Jeffrey Bury; Annette Trierweiler; Michel Baraer; Patrick J. Burns; LeeAnn Munk (pp. 1792-1801).

► We examined the dissolved and unfiltered trace element chemistry of a stream fed by glacier melt. ► Cation denudation was elevated in Cordillera Blanca proglacial melt with respect to other world glaciers. ► Water quality issues may arise as sulfide minerals are exposed by glacial retreat in the Cordillera Blanca, Peru. ► Several elements occur at concentrations deemed toxic to health.Globally, the ongoing retreat of mountain glaciers will ultimately diminish fresh water supplies. This has already begun in watersheds with greatly reduced glacial coverage. Still unknown are the affects of glacial retreat on downstream water quality, including the threats to human and ecosystem health. In the Cordillera Blanca, retreating glaciers have exposed sulfide-rich rock outcrops, negatively affecting the quality of the glacial meltwater. This study has evaluated glacial melt stream hydrogeochemistry in the sulfide-bearing Rio Quilcay watershed (∼9°27′S, ∼77°22′W) during the 2008 dry season. Surface water samples were collected from the upper 12km of the watershed during the 2008 dry season. Dissolved (0.4μm) and unfiltered acidified (pH<2) Al, Co, Cu, Fe, Ni, Mn, Pb, Zn and dissolved major ions and organic C (DOC) concentrations were quantified and pH and temperature were measured in the field. Twenty of 22 stream samples had pH values below 4, generating significantly ( p<0.01, α=0.05) greater cation denudation normalized to discharge than other worldwide glacier-fed streams. Additionally, dissolved trace and minor element concentrations were comparable to acid mine drainage. Non-conservative dissolved element behaviors resulted from adsorption/desorption reactions in tributary mixing zones. At low pH values, hydrous Fe oxides acted as the dominant sorption surfaces. The poor water quality observed in Cordillera Blanca headwaters coupled with the likely exposure of additional sulfide-rich outcrops from ongoing glacial retreat may pose water quality challenges.

Characterization of acid river dilution and associated trace element behavior through hydrogeochemical modeling: A case study of the Banyu Pahit River in East Java, Indonesia by Stephanie C.J. Palmer; Vincent J. van Hinsberg; Jeffrey M. McKenzie; Sophia Yee (pp. 1802-1810).

► The Kawah Ijen Volcano, Indonesia emits hyperacid toxic brines which are transported downstream by the Banyu Pahit River. ► Thermal springs add particulate Fe-(oxy)hydroxide which partly controls element concentrations, increasing Fe and metals. ► Upon mixing with neutral rivers, the Banyu Pahit precipitates Fe-(oxy)hydroxides and scavenges elements onto precipitates. ► Downstream the Banyu Pahit contains 15% hyperacid water, with the remainder from neutral rivers. ► The volcanogenic toxic load is almost entirely transferred downstream to the Asambagus Plain.Kawah Ijen volcano in East Java, Indonesia emits hyperacid (pH≈0) brines rich in toxic elements including F, Al, Cd and Tl, which are transported downstream by the Banyu Pahit River, which is eventually used to irrigate farmland on the Asambagus Plain. The fate and behavior of major and trace elements are investigated, in the region of greatest change to the Banyu Pahit River, where thermal springs and the neutral Kali Sat and Kali Senggon Rivers increase its discharge 6-fold and pH increases from 1.9 to 4.5 with the development of abundant precipitates. The conservative behavior of Cl, F and SO₄ allows determination of the proportions of the mixing constituents at each confluence. Comparing a mass balance model based on the resulting proportions with measured concentrations demonstrates conservative behavior for most cations, with the exception of Si, Zr, Sn and Ba, which precipitate as amorphous silica, barite, and Zr and Sn phases, respectively. Iron is added as particulate Fe-(oxy)hydroxide in mixing with thermal spring outflow, and dissolves in the lower pH water. This also contributes Co, Cd, Mn, Y, and the rare earth elements, which are desorbed from the Fe-(oxy)hydroxide upon entering the acid water. Subsequent saturation in Fe-(oxy)hydroxide after mixing with the neutral rivers leads to a reverse response. Still, element behavior is close to conservative, which means that the volcanogenic toxic element load is almost entirely transferred to the Asambagus Plain with ensuing environmental and health impacts. This study shows that compositions of these acid waters can be understood and reproduced in a thermodynamic model, but only when fine-tuned using measured compositions and field observations. Therefore, the model’s utility in assessing the fate of toxic elements and in planning the environmental mitigation is limited.

Seasonal fluctuations and mobility of arsenic in groundwater resources, Anchorage, Alaska by LeeAnn Munk; Birgit Hagedorn; Derek Sjostrom (pp. 1811-1817).

► We model the occurrence and speciation of dissolved As in groundwater. ► Most of the groundwater sampled has measured As concentrations that are above the USEPA drinking water standard of 10μg/L. ► Arsenic occurs primarily as As(III) and concentrations have a positive relation with seasonal fluctuations in water levels.There are approximately 12,000 private wells in the Municipality of Anchorage, Alaska, USA, that supply drinking water to thousands of homeowners. The results presented in this paper are from a study conducted to understand the speciation and seasonal fluctuations of As in the groundwater of Anchorage. A total of eight private drinking water wells were sampled from May to October, 2007, to determine inorganic species of As (III/V) and other physiochemical parameters of the groundwater. Arsenic concentrations above Environmental Protection Agency (EPA) drinking water standard of 10μg/L had been previously measured in all of these eight wells by the Municipality of Anchorage. Seven of the wells draw water from glaciofluvial aquifers and one well taps into the older bedrock aquifer on the mountain-side. In-situ measurements as well as groundwater samples were collected from each well and inorganic species of As (III/V) were separated in the field using anion exchange columns. Elemental analysis was conducted by inductively coupled plasma mass spectrometry (ICP-MS), major anions by ion chromatography (IC), and Fe (II) and total Fe were measured in the field with a portable spectrophotometer. The groundwater was neutral to basic ranging in pH from 7.6 to 8.8, dissolved O₂ was generally 0.1–1.0mg/L and specific conductance ranged from 300 to 1000μS/cm. Most of the groundwater is classified as Ca–Mg–HCO₃ and dissolved As concentrations ranged from below detection (∼0.5μg/L) to 117μg/L with arsenite as the dominant species. Filtered and unfiltered water samples had less than 1% difference in As concentrations suggesting that most As occurs in the dissolved form. Arsenic concentrations were positively correlated with water levels indicating that the highest As concentrations occur in the aquifer during recharge events. Positive relationships with dissolved Fe and supersaturation with respect to secondary Fe oxides indicates that the As is likely associated with the Fe oxides that are partially dissociated under the dominating reducing conditions of the aquifers. There is also evidence of a positive relationship between As andSO42- which indicates that some of the As may be associated with the oxidation of Fe-bearing sulfides such as pyrite or arsenopyrite, however, this is thought to be a less important process for this system compared to Fe reduction. Most of the groundwater samples indicate supersaturation with respect to carbonates such as calcite, dolomite and siderite and there is a positive relation between As andHCO3- indicating that carbonate buffering is an important process in the groundwater geochemistry of As. In some cases homeowners filter their tap water with household water treatment systems which have a range of As removal effectiveness from about 25–100%.

Total Hg concentrations in stream and lake sediments: Discerning geospatial patterns and controls across Canada by Mina Nasr; Jae Ogilvie; Mark Castonguay; Andy Rencz; Paul A. Arp (pp. 1818-1831).

► This article presents an analysis of 142,028 open-file data for total Hg concentrations (THg) in stream and lake sediments across Canada. ► THg was generally highest in areas affected by mining and smelting, followed by areas with high metallogenic source locations. ► Background THg dropped in sediments toward remote and cold locations, in accordance with the modelled atmospheric deposition rates for Hg. ► Mean THg was higher for upland than for lowland lakes and stream sediments, with THg(lake sediments) > THg(stream sediments). ► THg increased with sediment loss-on-ignition & trace-element content, and with increased basin drainage above the sampling locations.This article presents an analysis of Geological Survey of Canada (GSC) open-file data for total Hg concentrations (THg) in stream and lake sediments at 142,028 sampling locations. This analysis was done for select survey zones across Canada, with emphasis on discerning THg-relevant geographic, geological, atmospheric and topographic controls. THg was generally highest in areas affected by mining and smelting, followed by areas with high metallogenic source locations. Background levels for THg were elevated in the more populated areas along the south, but dropped toward the remote and coldest locations in the east, north and west. This trend was correlated ( R²=0.74; P<0.0001) with the 2005 GRAHM projections (Global/Regional Atmospheric Heavy Metals Model) for atmospheric Hg deposition (zones and locations with major geogenic sources and mining activities removed). Mean THg was higher for upland lakes (100.9±0.5 SE, ppb) and streams (71.7±0.6 SE, ppb) than for lowland lakes (94.4±0.86 SE, ppb) and streams (64.2±1.26 SE, ppb). The east-central portion of the Yukon Territory (Selwyn Basin) was analyzed in further detail. Here, THg within the sediments increased with increasing loss-on-ignition and increasing trace-element concentrations, and decreased with an increasing wet-area component per catchment above the sediment sampling locations. The characterization and quantification of these Hg trends is important for modeling and mapping health risks to ecosystems and communities across Canada and elsewhere.

Spatial and temporal evolution of Cu–Zn mine tailings during dewatering by Barbara L. Sherriff; D. Jared Etcheverry; Nikolay V. Sidenko; Jamie Van Gulck (pp. 1832-1842).

► This study evaluated the evolution of Ruttan Cu–Zn mine tailings on dewater. ► Very fine grained sulphides cause an initial pulse of metal and sulphate release. ► Metals temporarily attenuated as evaporite minerals form temporary metal sinks. ► The pH of tailings groundwater decreased first to 4.5 and then stabilized at 2–3. ► The metal content of ground water is increasing but is constant in Ruttan Lake.The Ruttan Cu–Zn mine produced about 50mT of fine-grained tailings over 30a. Since the closure of the mine in 2002, the tailings have been systematically dewatered through trenches draining into the open pit and underground workings. This study evaluated the evolution of tailings that were underwater until 2002, and also tailings that had been exposed to oxidizing conditions for more than 20a.Acid generation is dominated by the oxidization of the abundant pyrite and pyrrhotite comprising 25wt.% of tailings with Zn being mobilized from the sphalerite remaining after beneficiation of the ore. Little Cu is being mobilized partly due to the armouring of remnant chalcopyrite by primary quartz, and also by preferential absorption of Cu rather than Zn on secondary Fe oxy-hydroxides. A very fine grained fraction of unoxidized sulfides is a likely cause of an initial pulse of acid generation, and metal andSO42- release occurring at the onset of dewatering. Metals are temporarily attenuated from waters associated with the tailings, either absorbed on Fe oxy-hydroxide precipitates or as evaporite hydroxy sulfate minerals at the surface of the tailings. While some secondary phases are stable, evaporites are only temporary metal sinks as they redissolve in wet weather conditions. Trace amounts of calcite provide little buffering capacity resulting in rapid acidification of pore and surface water. The pH of pore water and shallow groundwater decreased first to the Al oxy-hydroxide buffer at 4.5 and then stabilized at values of 2–3 being controlled predominantly by the dissolution of solid Fe oxy-hydroxides. The metal contents of the ground and surface water are still increasing but the Ruttan Lake reservoir that receives drainage water from the tailings is maintaining a constant composition.

Source, attenuation and potential mobility of arsenic at New Britannia Mine, Snow Lake, Manitoba by Stephanie Simpson; Barbara L. Sherriff; Jamie Van Gulck; Elena Khozhina; Kathleen Londry; Nikolay Sidenko (pp. 1843-1854).

► The study investigated the aqueous passage of arsenic from an arsenopyrite stockpile. ► Arsenic is attenuated by adsorption to FeOOH in wetland soils and aquatic plants. ► Efficient natural attenuation limited the Snow Lake As concentration to 0.004mg/L.This study was to investigate the source, mobility and attenuation of As at the New Britannia Mine, Snow Lake, Manitoba. One major source of As contamination was determined to be an arsenopyrite residue stockpile (ARS) containing refractory Au in a waste rock impoundment. It appears that As is still moving through glacial clay at the base of the ARS into a confined aquifer even though the pile was capped in the year 2000. Arsenic is also being mobilized from a deposit of tailings, which formed following spills by previous owners, Nor Acme. Arsenic from the tailings is being mobilized by oxidation of arsenopyrite and reduction of arsenate to the more mobile arsenite by arsenate-reducing bacteria. This contamination is affecting a shallow unconfined aquifer and surface water flowing from the tailings through wetlands towards Snow Lake. Arsenic is being attenuated by adsorption to hydrated ferric oxides (HFO) in the tailings, wetland soils and aquatic plants. Although As in surface water, soils and plants along the flow path from the mine to Snow Lake are above Canadian drinking water guidelines, efficient natural attenuation by HFO in soils and plants of the wetlands have limited the concentration in Snow Lake to below drinking water standards.

Anthropogenic metal loads and their sources in stream sediments of the Meža River catchment area (NE Slovenia) by Mateja Gosar; Miloš Miler (pp. 1855-1866).

► High contents of Zn, Pb, Cr, Ni, Cu, Co were determined in the Meža River sediments. ► Metal-bearing phases were identified in sediments and assigned to three source areas. ► Main sources of metals in the Meža River sediments are mine waste deposits, iron-steel industry, bedrock weathering. ► Contribution of the Meža River to the total metal-load in the Drava River is evident.The Meža River Valley has been a center of mining, ore processing and iron- and steel-based metallurgical industry for more than 300 a. This paper deals with stream sediments draining this area. Loads of potentially toxic metals and metal-bearing phases were investigated 10 a after the cessation of Pb and Zn mining. Sediments in the upper Meža River Valley show significant pollution with Pb and Zn as a consequence of mining and ore processing. The highest contents of Pb and Zn were found in the Meža tributaries, which directly drain mine waste deposits (maximum values: 19,300mg/kg Pb and 37,900mg/kg Zn). These results reflect transport of contaminated material from mine waste sites and indicate that the inactive mine and its mine wastes are sources of metal contamination in the surrounding environment. Contents of Cr, Ni, Cu and Co are increased in the lower Meža River Valley, in the area of Ravne, as a result of the iron and steel industry. The contribution of the Meža River to the metal-load in the Drava River is evident.Metal-bearing phases, identified in stream sediments by SEM/EDS, are assigned to three areas, according to their source and genesis. The Mežica mining district source area is characterized by ore minerals of geogenic/technogenic origin (cerussite, sphalerite, smithsonite and galena), the Ravne source area is characterized by technogenic trace metal-bearing Fe-alloys, Fe-oxides and spherical trace metal-oxides and the Meža and Drava River catchment areas are represented by geogenic metal-bearing accessory and common rock-forming minerals, such as zircon, ilmenite, rutile, sphene, barite and monazite. SEM/EDS analyses of stream sediments agree well with the results of chemical analyses and they prove to be a very useful tool for identification of metal-bearing phases and their characterization according to source and genesis.

Environmental impact of ancient small-scale mercury ore processing at Pšenk on soil (Idrija area, Slovenia) by Tamara Teršič; Mateja Gosar; Harald Biester (pp. 1867-1876).

► Extreme mercury soil contamination as a result of small scale ore roasting activity. ► Hg contents above 5000 mg/kg determined in several soil and SOM samples. ► About 50 % of Hg in investigated soil and SOM samples are potentially bioavailable.The Idrija mine was the second largest Hg mine in the world surpassed only by the Almaden mine in Spain. It has been estimated that almost 145,000tons of Hg was produced during operation (1490–1995) of the mine. In the first decade of Hg mining in Idrija the ore was roasted in piles; after that it was roasted for 150 years, until 1652, in earthen vessels at various sites in the woods around Idrija. Pšenk is one out of 21 localities of ancient roasting sites established on the hills surrounding Idrija and one of the largest localities of roasting vessel fragments. The unique way of roasting very rich Hg ore at this site has resulted in soil contamination and considerable amounts of waste material that potentially leach Hg into the surrounding environment. The main aim of this study was to determine the distribution and the forms of Hg in contaminated soils in order to evaluate potential environmental risk. Detailed soil sampling was performed on 37,800m² area to establish the extent of Hg pollution and to investigate Hg transformations and transport characteristics through the 400 a-long period. A total of 156 soil (0–15cm and 15–30cm) and SOM (soil organic matter) samples were collected from 73 sampling points. Three soil profiles were sampled to determine vertical distribution of Hg. The main Hg phases were determined by the Hg-thermo-desorption technique. The measured Hg contents in soil samples in the study area vary from 5.5 to almost 9000mg/kg with a median of 200mg/kg. In SOM, Hg contents range from 1.4 to 4200mg/kg with a median of 20mg/kg. Extremely high Hg contents were found in soil profiles where the metal reaches 37,020mg/kg. In general, Hg concentrations in all three profiles show a gradual decrease with depth with the minimum values between 140mg/kg and 1080mg/kg. The Hg-thermo-desorption curves indicate the presence of Hg in the form of cinnabar and that of Hg bound to organic or mineral soil matter. The distribution of Hg species in soil and SOM samples show almost equal distribution of cinnabar and non-cinnabar Hg compounds. The non-cinnabar fraction shows a little increase with depth, but cinnabar represents a high portion of total Hg (about 40%). Large amounts of potentially mobile and transformable non-cinnabar Hg compounds exist at the roasting site, which are potentially bioavailable.

Anthropogenic gadolinium as a microcontaminant in tap water used as drinking water in urban areas and megacities by Serkan Kulaksız; Michael Bau (pp. 1877-1885).

► We provide data on rare earth element concentrations in tap water used as drinking water in Berlin, Germany, and London, UK. ► In contrast to the eastern part, tap water in western Berlin and in London shows high anthropogenic gadolinium (Gd) levels. ► Anthropogenic Gd is a micropollutant derived from contrast agents used in magnetic resonance imaging. ► 4-fold increase of anthropogenic Gd in Havel River from 1995–2010 suggests tap water Gd concentration will increase further. ► Anthropogenic Gd in river and tap water suggests high potential for presence of other waste water-derived xenobiotics.Gadolinium chelates have been used since 1988 as contrast agents in magnetic resonance imaging (MRI), and produce positive anthropogenic Gd anomalies in rare earth element (REE) patterns of river and lake waters. These Gd compounds are not removed in wastewater treatment plants (WWTP) due to their high stabilities, and are transferred to surface waters with the clearwater discharge from WWTP. Through natural and induced bank filtration, the anthropogenic Gd is also transported into groundwater. To date, there are no related acute health risks known, but the potential long-term effects of exposure to low doses have not been studied.Here REE data is presented for tap water from the City of Berlin, Germany, a metropolitan area that is known for its anthropogenic Gd-rich rivers and groundwater. Natural and induced bank filtration play important roles in Berlin’s freshwater resource management. Therefore, the extent to which municipal tap water that is used as drinking water is affected by anthropogenic Gd was investigated. Large positive Gd anomalies were found in tap water samples from the western districts of Berlin, indicating the presence of up to 18ng/L of anthropogenic Gd on top of a geogenic background of 0.54ng/L. In marked contrast, the amount of anthropogenic Gd in tap water from the eastern districts of Berlin is negligible to minor (maximum of 0.18ng/L on top of a geogenic background of 0.26ng/L). This strong regional difference likely results from the specific historical situation of Berlin, where before the re-unification of Germany in 1990, natural and induced bank filtration were necessities in isolated West Berlin, but unimportant in East Berlin, a situation that has seen little change during the past 20 years. Thus, drinking water resources in the western part of Berlin are more strongly affected by anthropogenic Gd than those in the eastern part. The high anthropogenic Gd concentrations found in some tap waters in Berlin clearly show that the Gd initially used as contrast agent is removed neither during natural nor artificial water treatment. This is further evidence for the high stability and long environmental half-lives of these compounds. Considering that the amount of anthropogenic Gd in the Havel River in Berlin has increased more than 4-fold over the past 15 years and that water migration from the Havel River to the groundwater wells take years to decades, the amounts of anthropogenic Gd in West Berlin tap water will increase further over the next few years. Due to its presence in tap water that is consumed as drinking water, millions of people are exposed to low doses of these anthropogenic Gd chelates. Additional data for the City of London, UK, for example, indicate that this is not a local phenomenon confined to the City of Berlin, but rather a common feature of tap water in metropolitan areas and megacities in countries with highly developed health care systems. Hence, the REE distribution in tap waters used for human consumption should be monitored, especially since the anthropogenic Gd chelates can also be used as tracers for emerging microcontaminants such as steroids, pharmaceuticals and personal care products.

The long term operation of a biologically based treatment system that removes As, S and Zn from industrial (smelter operation) landfill seepage by Mattes Al; Les J. Evans; W. Douglas Gould; W.F.A. Duncan; Susan Glasauer (pp. 1886-1896).

► A passive treatment system removed arsenic, zinc and sulfate from mining impacted water to discharge concentrations. ► The concentrations of metals and sulfate were reduced mainly in the two anaerobic bioreactors rather than in the three plant based cells. ► The sequestered elements were removed by biotic and abiotic mechanisms, including sorption, precipitation and filtration. ► The treatment system was resistant to seasonal fluctuations and spikes in input metal concentrations. ► The system has a relatively long life span of more than 10 years for a passive bioreactor system treating metals.Passive treatment systems have a long history in the remediation of mining impacted water. The functioning of these systems is poorly understood, in particular the microbial processes that underpin metal removal. A biologically based engineered wetland treatment system that has operated in Trail, B.C. to treat seepage from a historic Pb and Zn smelter landfill, was investigated. The system has functioned for more than a decade, an unusually long life span for a passive bioreactor design. The study focuses on the 5a of operation from 2003 until 2007. Arsenic is a major contaminant in the ore that is processed in Trail, which has caused high As concentrations in the seepage. In addition to As, Zn and Cd removal were investigated. During the 5-a period, the system sequestered 2990kg of As, 7700kg of Zn and 85kg of Cd. Nearly 90% of these elements were removed in two biochemical reactors (BCRs) that comprise the first two components of the six cell system, with the remainder removed in plant-based polishing cells. Average input concentrations over the 5-a period were 2.3 and 4.1mM for As and Zn, respectively and 0.45μM for Cd. Final output concentrations were reduced to 0.01mM for As, 0.05mM for Zn and 0.18μM for Cd. Sulfur removal averaged 34% of input concentration. Analysis of mineral formation in the system using X-ray diffraction and scanning electron microscopy indicated kottigite (Zn₃(AsO₄)₂⋅8H₂O) and sphalerite (ZnS) as the major mineral phases controlling As and Zn sequestration; Cd appears to be immobilized as CdS. Evidence for orpiment was obtained from X-ray absorption spectroscopy (XANES) studies, and arsenopyrite was not detected. Although microbial activity dominates the removal of Zn, As and Cd from the soluble phase, abiotic removal mechanisms contribute including sorption of As and Zn to biosolids and filtration of metal precipitates by the solid matrix. The removal of toxic elements over the period appeared to be relatively consistent. Seasonal fluctuations, a large spike in input element concentrations over a 2-month period, and removal of the two biochemical reactors during a period of reconstruction appeared to have relatively little impact on the system as a whole.

Eolian deposition of trace elements onto Taylor Valley Antarctic glaciers by Sarah K. Fortner; W. Berry Lyons; John W. Olesik (pp. 1897-1904).

► We examined trace element concentrations in glacier snowpits located within the same valley. ► Variation between the chemistries of Taylor Valley, Antarctica snowpits related to eolian deposition. ► Crustal sources contributed most of the trace elements to Taylor Valley Antarctic snow. ► Eolian deposition is important to the availability of nutrients and potentially toxic elements in Taylor Valley, Antarctica.The major ion and trace element chemistry in four 60–110cm deep snow pits was examined from three Antarctic Taylor Valley glaciers (Commonwealth, Canada and Howard), all located within 20km of the Ross Sea. Taylor Valley (TV) (77°30′S, 163°15′E) is part of the McMurdo Dry Valleys (MDV), the largest ice-free area in Antarctica. Snow chemistry of these glaciers is strongly influenced by cross-valley (SW–NE and NE–SW) winds that deposit eolian materials, including mineral dust and soluble salts. Arsenic, Cd, Cu, Mo, Pb, Sb and Sn in recent TV glacier snow are almost exclusively derived from eolian dust. The relative magnitude of element variations with depth relate to the exposure of snow sites to prevalent winds. Eolian deposition is a primary source of these elements to Canada Glacier snow and supra and proglacial streams. Eolian processes are likely very important to the delivery and availability of nutrients and, potentially toxic elements to dry valley Antarctic ecosystems.

Hg concentrations and accumulations in fungal fruiting bodies, as influenced by forest soil substrates and moss carpets by Mina Nasr; Paul A. Arp (pp. 1905-1917).

► Increasing soil S decreases basidiomatal Hg uptake. ► Increasing basidiomal S increases basidiomatal Hg. ► Basidiomatal Hg concentrations decrease from basidiomatal emergence to maturity. ► Annual basidiomatal uptake from soils is estimated to be small relative to total Hg pool within soil. ► Basidiomatal Hg up increases with increasing Hg concentrations within forest litter and mosses.This article summarizes trends in total Hg concentrations (THg) in fungal fruiting bodies (basidiomata) and their underlying soil substrates in the absence and presence of surrounding moss layers. Three forest locations across south-western New Brunswick spanning from a central mainland location to Grand Manan Island in the Bay of Fundy were chosen for the study. Geographic location had an effect on THg in the soil layers and in the basidiomata (THg on island>THg along the mainland coast>THg mainland) but this effect was weak and probably obscured by the large THg variations within the basidiomata and their soil and moss substrates at each location. Within the soil, THg increased with increasing total organic S (TS) and C (TC) concentrations, and depended on type of moss cover if present. Within the mosses, THg varied by species, by moss-internal TS, and by THg and TS within the underlying soil. Basidiomatal THg also varied strongly by species, and was further affected by: (i) developmental stage, from emergence to senescence, (ii) cap versus stalk, (iii) basidiomatal TS, and (iv) soil THg, TS and TC. These variations and their interdependencies were explored and quantified by way of multiple regression analyses. Basidiomatal bioconcentration of soil THg (F layer) varied strongly by species as well. Basidiomatal Hg extraction from the soil was estimated to be small in terms of reducing the accumulated Hg loads within the soil, but represents a re-entry point of Hg into the local food chain.

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Applied Geochemistry (v.26, #11)