Foundations for the study of vertical metal distributions in lacustrine sediments

Alpay, S.¹, J.J. Veillette² and M. Douma²

¹ Mineral Resources Division, Geological Survey of Canada, Ottawa ON
² Terrain Sciences Division, Geological Survey of Canada, Ottawa ON

Metals are commonly more concentrated near the sediment-water interface than in deeper lake sediments. These observations are widely reported and have been attributed to increased anthropogenic deposition and/or to vertical diagenetic remobilization. The Geological Survey of Canada - Metals in the Environment (GSC-MITE) Initiative has established a second phase of lake sediment studies in the Rouyn-Noranda region to explore the relative effects of chronological metal loading and diagenetic metal remobilization in lake sediment profiles. A multi-disciplinary research team has been formed to integrate evidence from biological indicators with quantitative mineralogical, geochemical, microbial, and numerical approaches to understanding the processes of early diagenesis in a freshwater system.

Two kettle lakes, Lac Perron and Lac de la Pépinière, were selected from within the zone of influence of the Horne smelter in Rouyn-Noranda (Quebec) from 100 lakes studied in a reconnaissance survey (Phase I of the GSC-MITE lake sediment studies; Kliza and Telmer, 2001). The kettle lakes formed in depressions in thick glaciofluvial deposits. Among the major selection criteria were: diatom evidence of increased lake water acidity over time, geographic orientation with reference to the major wind directions from the smelter, and no obvious metal loading from local point sources other than the Horne smelter.

The foundations for this study include its rationale, research strategies, and lake settings chosen. These are essential contextual data from which emerging analytical results of diatom studies, pollen counts, quantitative mineralogy, solid and aqueous phase geochemistry, isotopic determinations, and bacterial enumerations, can be interpreted and integrated.

Reference
Kliza, D. and Telmer, K., 2001. Phase I. Lake sediment studies in the vicinity of the Horne smelter in Rouyn-Noranda, Quebec. Geological Survey of Canada Open File D2952, CD-ROM.

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Analysis of water samples for ‘total dissolved' mercury: collection, filtration and preservation

Hall, G., P. Pelchat, J. Vaive

Mineral Resources Division, Geological Survey of Canada, Ottawa, ON

The study objective was to determine the most cost-effective and efficient procedures by which to sample, filter (0.45 m) and preserve surface waters for the accurate determination of Hg (‘total dissolved'). The following parameters were studied: bottle materials; bottle cleaning methods; Hg vapour transmission through different bottle materials; 0.45 m-filter system; and preservation method. Mercury was determined by CV-ICP-MS to a detection limit of 0.5 ppt.

The bottles studied comprise: Teflon (FEP); high density polyethylene (HDPE); polyethylene terephthalate copolyester (PETG); polypropylene (PP); and precleaned HDPEP. EPA Methods 1631 and 1638, and a triple rinsing with distilled deionized water were evaluated. Three preservation media were tested: 0.5% BrCl; 2% HCl; and 0.04% K2Cr2O7 in HNO3. A separate experiment was carried out to compare the transmission of Hg vapor through the 125-ml bottles.

Twelve filter systems were tested for their potential contribution of Hg to a water sample. Immediately after filtering Type I water, each sample was stabilized in 0.5% BrCl and subsequently analysed. The filter systems were also tested for retention of Hg during filtration; Ottawa River water and Type I water, both spiked at 55 ppt Hg, were used in this test.

In summary:

1. All bottle types can be used without any cleaning (i.e. rinsing only) for the determination of Hg in waters down to levels of <0.5 ppt. None of the commonly used preserving agents (BrCl, HCl or K2Cr2O7 in HNO3) appears to leach out detectable concentrations of these elements from the bottle material. Thus, the elaborate cleaning methods, EPA 1631 and 1638, can be avoided for Hg;
2. As the PP and HDPE bottles are inexpensive and robust, they are highly recommended. Although the Hg vapor transmission study showed the order of transmission to be Glass<PET<FEP<PP<HDPE<LDPE, the potential for contamination from outside the bottle; via an airborne source is negligible. If the storage area is high in ambient Hg, PP is preferred.
3. All data for the filtered Type I water through the 12 different systems were below 0.5 ppt Hg. However, spiked Hg in the Ottawa River control and Type I water was not fully recovered using any of the filters (ca 80% recovery using the Millipore Durapore membrane filters to only ca. 30% with Gelman's Supor membrane systems); and
4. The stability of Hg, preserved in 0.5% BrCl in the four spiked control samples was excellent (55±2 ppt over the 28-day period). Preservation in 2% HCl or 0.04% K2Cr2O7 showed a slight decrease of about 10-20%, though this was sample dependent (and independent of bottle type). This apparent decline in Hg may be due to a partial species transformation upon spiking, from Hg2+ to an organic complex (especially in the Ottawa and Rideau Rivers), which might occur in the HCl- and K2Cr2O7-preserved samples.

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Effects of air drying on element forms in lake sediment cores

Hall, G., J. Vaive, P. Pelchat, G. Bonham-Carter, D. Kliza, K. Telmer

Mineral Resources Division, Geological Survey of Canada, Ottawa, ON

Under the MITE Initiative of the Geological Survey of Canada, lake sediment cores were collected in the vicinity of, and remote from, the Horne smelter and refinery complex in the city of Rouyn-Noranda, Quebec. A sub-project of this work focuses on establishing the optimum method of preserving and preparing lake sediment cores for sequential extraction analysis used to identify the phases in the sediment with which the elements are associated. Air drying is a practical method often employed to prepare samples for selective extraction analysis, but exposure to air can change the element distribution amongst phases; this work compares the results of sequential extraction analysis on air-dried and wet samples.

Two lake sediment cores (<35 cm) were studied, from Gravel Pit and Green Lakes. The former lake is 9.5 km from the smelter, 4 m deep and only about 0.07 km2 in surface area; the corresponding parameters for Green Lake are 75 km, 19 m and 0.24 km2, respectively. The core was extruded onto a Plexiglass platform and subsampled with a plastic spatula at 1-cm intervals directly into Whirlpak™ bags that were squeezed to expel entrained air. Samples were immediately put into iced coolers in the field and then kept in a fridge at 4 C. Just prior to analysis, the samples were separated into two batches: one suite (‘wet') for immediate treatment (centrifuging and extraction), and the second (‘dry') for air-drying followed by extraction. Phases nominally separated by the sequential extraction are: ‘adsorbed/exchangeable/carbonate' (‘AEC'); soluble organics (‘ORG'); amorphous Fe oxides (‘amFeox'); crystalline Fe oxides (‘cryFeox'); and sulphides, residual organics by aqua regia digestion (AR).

An earlier study on cores from Meech Lake had shown that sequential extraction results on samples that had been dried by air- and freeze-drying agreed with each other and were significantly different from those obtained on the wet sample stored at 4 C. Results for Green and Gravel Lakes show that element behavior is matrix-specific and therefore unpredictable. For example, Fe in the AEC, ORG and amFeox phases in Meech Lake decreased significantly upon drying whereas, in Green Lake, Fe in the amFeox and cryFeox phases increased at the expense of Fe by AR. Thus, changes in element distribution amongst phases on drying the sediment are both matrix- and element-dependent. Ultracentrifuging proved necessary for samples with high contents of clay-sized material that would be peptized in solution in the acetate and phosphate leaches, and hence cause erroneously high results for elements such as Si, Ti and Fe in those phases. Often the element pattern in each phase down the core would be similar (wet vs. dry) but differ in intensity. On drying, enrichments in the top 12 cm of elements such as Bi, As, Sb, Pb and Tl would be increased in the first four phases at the expense of the AR component. Some elements such as S, Be, Sc and Zn showed no changes between dry and wet samples. The most dramatic changes usually occurred in the first three phases, which is particularly pertinent to studies focusing on bioavailibility and sorption of metals. Maintaining the sample wet at ca 4 C prior to selective leaching is recommended for the most accurate results of selective extraction.

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Regional distribution of trace metals in soils surrounding a Cu smelter in the Boreal Shield ecozone, northern Quebec, Canada

Henderson, P.J., R.D. Knight and I. McMartin

Terrain Sciences Division, Geological Survey of Canada, Ottawa, ON

Soil sampling was undertaken in the vicinity of the Horne smelter at Rouyn-Noranda, Quebec, as part of the Geological Survey of Canada MITE Initiative. The study examined variations in trace metal concentrations in soils, and the underlying glacial sediments, with the objective of identifying criteria for differentiating anthropogenic from geogenic metal enrichment, and determining the fate of smelter-derived metals in the environment.

Bedrock in the area consists of highly mineralized Abitibi Greenstone Belt rocks. Soils are developed on glacial sediments, primarily till (podzols) and glaciolacustrine clays (luvisols), and it is assumed that soil-forming processes started immediately after deglaciation approximately 8,000-10,000 yr BP. The Horne smelter has operated since 1926, and at the time of the study (1998) annually emitted 923 tonnes of particulates, including 150 t Pb, 70 t Cu, and 39 t Zn. By 2001 major reductions had been achieved to 595 t of particulates (65 t Pb, 42 t Cu and 18 t Zn).

Humus, B-horizon (10-15 cm depth) and C-horizon (80-90 cm depth) soil samples were collected at 106 sites within a 100 km radius of the smelter. The <2mm size fraction of both humus and mineral soil samples was analyzed geochemically using inductively coupled plasma atomic emission spectrometry after Aqua Regia digestion. In addition, humus samples were subjected to a sequential extraction scheme designed to nominally separate the following phases: (1) soluble organics, (2) amorphous and crystalline Fe oxides, (3) sulphides and insoluble organics, and (4) silicate and other resistant minerals. Mineral soils were analyzed using leaches selective for separation of amorphous Fe oxide phases and residual (silicate) mineral phases. Organic matter content and soil pH were measured. Geochemical results are plotted against distance from the smelter and separated according to soil parent material (till vs. glaciolacustrine clay).

Results indicate that smelter-derived metals (Ag, As, Cd, Cu, Pb, Zn) are enriched in humus near the smelter and decrease in concentration with distance, depending on the element and dominant wind direction. The relative extent of metal enrichment (over background) is in the order Cu=Cd>Pb=Ag>As>Zn. The residence sites of metals in humus varies depending on the metal. For the smelter-derived metals Cd, Pb and Zn, >50% of the total metal is held in the labile, soluble organic phase, for Cu and As, ~25% is held in the soluble organic phase. Factors affecting metal mobility in humus include total concentration, soil pH, and parent material.

Metal concentrations in mineral soils vary depending on the soil horizon, effectiveness of downward leaching from contaminated humus, bedrock geology and parent material. Factors affecting metal mobility include the total concentration and mobility of the element in the overlying organic horizon, and the composition and texture of the parent material, which affects permeability and pH.

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Detecting metal emissions in the snowpack around the Horne Smelter, Rouyn-Noranda, Quebec.

Kliza¹, D., C. Zdanowicz², G. F. Bonham-Carter¹, D. Paktunc³, G.E.M. Hall¹ and J. Vaive¹

¹ Mineral Resources Division, Geological Survey of Canada, Ottawa, ON
² Terrain Sciences Division, Geological Survey of Canada, Ottawa, ON
³ Applied Mineralogy Lab., Canada Centre for Mineral & Energy Technology, Ottawa, ON

Snow was collected around the Horne copper smelter in Rouyn-Noranda (Quebec) in February 2001 to determine the abundance, size distribution and elemental composition of metal-bearing particles deposited into the snow pack. Samples were collected from 26 sites at distances of 2 to 277 km from the smelter, primarily downwind. One thousand particles (> 0.45 m diameter) were analysed in each snow sample using an automated Variable Pressure Scanning Electron Microscope (VP-SEM) equipped with an Energy Dispersive X-Ray analyser (EDX). For each particle the area was measured and X-ray counts were collected for 19 elements: Na, Mg, Al, Si, P, S, Pb, Cl, K, Ca, V, Cr, Fe, Ni, Cu, Zn, As, Se and Cd.

The various elemental associations found in the particles were investigated using mathematical and statistical tools. Non-hierarchical cluster analysis was applied to the VP-SEM data to identify the major compositional types of particles. Particles fall into two broad categories; geogenic (primarily Al, Si, Fe, Ca, K and Mg) and metal-bearing, most likely smelter-derived particles (primarily Zn, Cu, Pb, Cr with S). In all snow samples, the most abundant particles by far (75 to 85 %) were Al+Si, which may comprise biogenic silica (e.g., freshwater diatoms) but probably include abundant fly-ash with a Si-glass composition. These findings are in good agreement with electron microscope observations made by others on surface soil samples collected within the smelter-affected area. The most abundant metal-bearing particles are Fe+Cu+S (0.5 %), Fe+S (0.3 %), and Zn+S (0.2 %), but many other associations were found that include V, Se, As and Ni. The greatest percentages of metal-bearing particles in snow are found within 50 km of the smelter. In particular, the abundance of Cu+S, Cu+Fe+S and Zn+S-type particles decreases in a nearly logarithmic pattern with increasing distance from the smelter. This pattern is similar to that observed for total Cu, Fe and Zn concentrations in the snowpack.

Particles in snow range in size (area) from 0.3 m2 (SEM detection limit) to 1409 m2. The size distribution modes show little variation between sample sites, with a mean mode of 1.8 m2 (± 2.4 m2). The size distributions for specific (e.g., Cu) metal bearing particles are similar to the size distribution of the total particulate load at the same sites. This is noteworthy as the metal bearing particles only represent <25% of all particulates. There is no obvious relationship between maximum particle size and distance from smelter. Exceptionally large (1000 m2) metal-bearing particles were even found in samples over 200 km from the smelter. Data from this SEM study will be compared with the geochemical analyses of the particulates recovered from duplicate samples collected at the same sites in February 2001.

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The effects of weathering and soil-forming processes on geochemical background

Klassen, R. A.

Terrain Sciences Division, Geological Survey of Canada, Ottawa, ON

To establish trace metal associations and residence sites in terms of mineralogy and weathering, soil profiles in different geological terrains were studied by microbeam techniques, and by geochemical analyses of sand-silt-clay-sized (< 2 mm), silt and clay-sized (<0.063 mm), and clay-sized (<0.002 mm) soil fractions using hydroflouric-nitric-perchloric acids, Aqua Regia, and hydroxylamine hydrochloride digestions. In each profile, samples were collected in contiguous 5 cm vertical increments to depths of c.70cm; below that depth samples were spaced at intervals 10cm. Soil parent materials are derived from varied bedrock types, including sulphide-bearing marble, black shale, and ultramafic igneous rock, all of which can have natural trace element concentrations (As, Zn, Hg, Ni, Cr) exceeding threshold levels set for purposes of environmental regulation.

The geochemical properties of mineral grains were established by microbeam analysis using Scanning Electron Microscopy linked to an Energy-Dispersive X-ray Spectrometer with mapping capabilities (SEM-EDS), selected grains were further analyzed by Secondary Ion Mass Spectrometry (SIMS). Major and minor elements (e.g., Si, Al, Ca, Na, Mg, K, Fe, Ti, Mn and S) were used to infer the mineralogy of grains in the fine sand and silt (5 to 100 m) fractions, and to establish linkages between minerals and trace metals, and the effects of weathering on them.

In soil profiles, trace element concentrations vary systematically with depth, with the greatest rate of change in the uppermost 50 cm (A and B soil horizons). Some trace elements (As, Cu, Cr, Ni, Pb) increase downward to maximum values in the C soil horizon, whereas others decrease (Hg, Zn). For trace elements that increase downward, linear relations are observed with lithophile elements (Al, K, Mg) that indicate the metals (Aqua Regia acid digestion) are held in Mg-bearing mineral structures, probably Mg-bearing phyllosilicates. Differences among A and B, and C soil horizons reflect the relative rates of removal of lithophile and trace elements during weathering. For Cu, Ni, Pb, and Cr the work indicates that Mg-bearing phyllosilicates are key to the interpretation of natural background variations, and that weathering of phyllosilicates controls the transformation of metal to more labile and bioavailable forms. Concentrations of elements which decrease downward in the upper solum (e.g., Zn, possibly Hg) appear to be controlled by abundance of organic matter more than by inorganic minerals.

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Mineralogy of fine-grained sediment by energy dispersive spectrometry (EDS) image analysis – a methodology

Knight, R.D.¹, R.A. Klassen¹, P. Hunt²

¹ Terrain Sciences Division, Geological Survey of Canada, Ottawa, ON
² Mineral Resources Division, Geological Survey of Canada, Ottawa, ON

Energy-dispersive X-ray spectrometry (EDS) image analysis is well suited to mineralogical analyses of fine sand and silt-sized grains (0.425 – 0.010 mm), a size fraction not amenable to quantification by other mineralogical methods. This methodology can map, characterize, and quantify physical and chemical properties of large numbers of grains (50-300), permitting mineral identification at concentrations as low as 1%. As such, EDS microbeam analysis has potential application to a wide range of geological, geochemical, and environmental studies.

Soil samples were collected as part of a wider study by the Geological Survey of Canada on soil geochemistry, weathering and soil-forming processes. The samples selected for study were from diverse geographic and geological terrains of Canada, and included both weathered and unweathered material.

Until recently the main hindrances to mineral identification and mapping by EDS image analysis were technical, related to the long acquisition time required to obtain images and computing limitations. Recent increases in computer speed, storage capacity, and connectivity now permit rapid collection, compilation, and analyses of EDS images by desktop computers. Automation of EDS data acquisition allows overnight operation, thus maximizing equipment utilization. Further, transfer of digital images permits post-capture data processing on equipment unrelated to the detector, thereby freeing laboratory resources.

In common with clast analysis, EDS image analysis can be used to discriminate facies, provenance, and origin of fine-grained materials. In partitioning studies it can be used to quantify mineralogical differences among grain size categories, and to establish mass balance relations between source terrains and sediments derived from them. Relative differences in composition and in mineral shape can also be used to infer weathering and sedimentological processes related to erosion, transport and deposition. In provenance studies, geochemical analyses are more difficult to interpret, due to a reliance on element ratios and assumptions about element mobility in the weathering environment, than the mineralogical data generated by EDS image analysis. For weathering studies, EDS image analysis can identify and map alteration within grains with respect to mineral species and a mineral's position in the soil profile. Importantly, it can also be used to identify rare or unusual mineral grains and their location on the sample stub for further study using other investigatory tools such as the electron microprobe or secondary ion mass spectrometer (SIMS). Unusual minerals include indicators sought for mineral exploration, unique indicators of bedrock provenance, or environmental tracers such as smelter particulates.

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Comparison of Cu-Hg-Ni-Pb concentrations in soils adjacent to four Canadian anthropogenic point sources

McMartin, I., P. Henderson, A. Plouffe, R. Knight

Terrain Sciences Division, Geological Survey of Canada, Ottawa, ON

The extent and variation of Cu, Hg, Ni and Pb loadings in soils was examined in the vicinity of four industrial sources of airborne metal particulates. Metal enrichment and the depths to which metal emissions penetrate soils near anthropogenic point sources depends on numerous site-specific factors (e.g., history and nature of emissions, distance from point source, wind patterns, nature and composition of parent substrate and climate). These factors have been evaluated at several sites in Europe and North America, but few studies compare metal distribution in soils in the vicinity of several point sources located in different ecozones and geological terrains. This work compares metal loading in soils at sites with both anthropogenic metal inputs and high natural metal backgrounds: the Cu smelter at Rouyn-Noranda, Québec; the Cu-Zn smelter at Flin Flon, Manitoba; the Pb-Zn smelter at Trail, BC; and the inactive Pinchi Lake Hg Mine, BC.

Metal distribution was examined in 78 soil profiles (humus, B-horizon, C-horizon) near the four facilities. The substrate consisted predominantly of glacial sediments, and soils at all locations were either podzolic or brunisolic. Samples were air-dried at room temperature and dry-sieved (stainless steel) to recover the <2 mm fraction. Organic and mineral soil samples were analyzed for Cu, Ni and Pb by ICP-AES following an Aqua Regia digestion; Hg was determined by cold-vapor atomic absorption spectrometry. Total organic matter content was determined by weight loss on ignition (% LOI) after heating a small portion at 550 C for one hour.

Concentrations of emitted metals are elevated in the surface organic-rich horizons of soils near Rouyn-Noranda (Pb>Cu), Trail (Pb>Cu>Hg), Flin Flon (Cu=Pb>Hg) and Pinchi (Hg), and decrease with increasing distance from the source according to simple regression models. Integrations under the regression models generally show a good relationship to the estimated historical emissions. Humus is therefore capable of effectively retaining the deposited metal emissions near the facilities. Some evidence for leaching of metal contaminants from the humus into the mineral soils is seen at Trail, where Pb accumulation in the B-horizons is observed to a distance of at least 20 km from the smelter, and at Flin Flon and Rouyn-Noranda, where the B-horizons of sites located within 10 km of the smelters can be contaminated by smelter-related metals. The metal content of the C-horizons soils at any of the four locations is predominantly controlled by the nature and composition of the substrate, there is no indication of sub-surface contamination of these mineral soils. Anthropogenic contamination in soils is assessed by comparing metal concentrations in surface organic layers to those in the underlying uncontaminated mineral soils. Hg and Pb exhibit the highest humus:C-horizon metal ratios, up to 1000 near the point sources, and averaging 10 at background sites. These high ratios are due to the particular affinity of Hg and Pb for organic matter. Comparisons of these ratios between the four sites are useful for estimating distances from the point sources at which natural processes re-assert themselves.

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Mercury, antimony, nickel, and zinc in soils near two past-producing mercury mines, British Columbia

Plouffe¹, A., G.E.M. Hall², and P. Pelchat²

¹ Terrain Sciences Division, Geological Survey of Canada, Ottawa , ON
² Mineral resources Division, Geological Survey of Canada, Ottawa , ON

The Pinchi fault region, located in central British Columbia, is naturally enriched in mercury because of the abundance of cinnabar (HgS) mineralization in bedrock. Two mercury mines were active in the region: the Bralorne Takla and Pinchi Lake mines.

The aim of this study is to identify the source of mercury in soils, that is to determine if the observed high mercury levels are related to natural processes (e.g., metal cycling in soil, glacial dispersal from the mineralized bedrock) or to anthropogenic activities (mining).

Humus, B-horizon and C-horizon soil samples were collected along sampling transects which start in the vicinity of both mines and extend up to 85 km from the mines, into regions with naturally elevated mercury concentrations. The <2 mm size fraction of all samples was analyzed by a combination of ICP-AES and ICP-MS following two leaches applied in sequence and designed to estimate the metal concentrations held in labile and non-labile phases of humus and mineral soils.

Mercury concentrations are highest in humus in both labile and non-labile phases near the Pinchi Lake and Bralorne Takla mines, and rapidly decrease with increasing distance from the mines. Such enrichments in humus are not observed in regions distant from the mines where the mercury concentrations are naturally elevated in the underlying soil parent materials. Consequently, the mercury enrichment in humus near both mines is proposed to be in part due to anthropogenic contamination. On average, 95% of the mercury in humus is held in a non-labile phase which is dominantly HgS dust (cinnabar ?) as identified with a variable pressure scanning electron microscope. The remainder of the mercury is labile and likely loosely bound to organic matter. Elevated mercury concentrations in the B- and C-horizons (80% in non-labile phases on average) are related to natural sources: bedrock and glacial sediments.

Antimony is found in association with the mercury mineralization in bedrock at the Pinchi Lake mine. Consequently, antimony might have been emitted during the mining operations. There is an antimony enrichment in humus (95% in non-labile form) near both mines which decreases with increasing distance. The enrichment may be related to anthropogenic contamination or natural biogeochemical cycling, most likely a combination of both.

Zinc and nickel were not processed or emitted at the mines. Zinc and nickel enrichments in the soils are derived from bedrock and glacial sediments naturally enriched in these metals.

This research was conducted as part of the GSC Metals in the Environment Initiative.

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Natural and anthropogenic metal fluxes to marine sediments near a primary lead smelter in New Brunswick, Canada

Parsons, M., R. Cranston

Geological Survey of Canada (Atlantic), Dartmouth, NS

Significant variations in Cd, Cu, Hg, Pb and Zn concentrations occur in surficial marine sediments collected in the Bay of Chaleur, an estuary located between northern New Brunswick and Québec's Gaspé Peninsula. The bay receives metals from a variety of sources including a lead smelter, two thermal generating stations, a mercury-cell chlor-alkali plant, and numerous mined and unmined base-metal deposits. The purpose of this study is to assess the fluxes and dispersal patterns of metals released to the bay from both natural and anthropogenic sources, and to characterize the processes that collect and redistribute metals in the marine environment.

Gravity cores and grab samples of marine sediments were collected from 130 sites in the Bay of Chaleur, in water depths of 2 to 95 m and at distances up to 100 km away from the smelter. The sediments were subsampled within 24 hours of collection for analyses of metal concentrations, lead isotope ratios, carbon contents, and grain size. Sediment pore waters were extracted from the cores using centrifugation and analyzed in the field for dissolved ammonium, sulfate, and salinity. These pore water data were used to estimate present-day sediment accumulation rates.

Chemical analyses of 925 sediment subsamples show the following ranges in metal concentrations (mg/kg): Cd, 0.02–69; Cu, 3–200; Hg, <0.01–2.4; Pb, 0.3–2040; and Zn, 22–3200. The highest concentrations of these metals occur in surficial sediments within 5 to 10 km of the smelter. Metal concentrations in harbour sediments adjacent to the smelter are highest at approximately 5 cm depth and decrease progressively towards the sediment surface, which may reflect the significant reduction in smelter emissions since the mid-1980s. Anomalously high concentrations of Hg and Cd, Cu, Pb and Zn also occur within 1 km of the chlor-alkali plant and a decomissioned Cu-Zn concentrate loading facility, respectively. Analyses of ammonium and sulfate gradients in the sediment pore waters, vertical profiles of Fe, Mn and organic carbon in the solid phase, and grain size variations indicate that the metal profiles in most cores are not caused by sampling artifacts or diagenetic remobilization. Lead isotope ratios show that Pb in the contaminated surface sediments is less radiogenic than the natural background Pb. Comparison of Pb isotope ratios in the sediments with published isotopic data for geogenic and anthropogenic sources suggests that the surface enrichment of Pb throughout most of the bay is mainly derived from historical combustion of Canadian leaded gasoline and smelter emissions.

This study indicates that the flux of metals to most areas of the Bay of Chaleur has increased in recent years relative to pre-industrial times. This is especially true for Pb, which is present in surface sediments throughout the entire bay at concentrations that are at least three to four times background values (0.3–6 mg/kg). Dispersion of smelter effluents and emissions by wind and/or near-shore currents has resulted in an area of elevated Cd, Cu, Hg, Pb and Zn concentrations in surficial marine sediments within approximately 20 km of the Brunswick smelter.

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Hg cycling in Kejimkujik Park, Nova Scotia: Lessons learned

Rencz, A.and O'Driscoll, N.

Mineral Resources Division, Geological Survey of Canada, Ottawa, ON

Kejimkujik Park, Nova Scotia, is noted for having the highest mercury concentrations in loon blood in North America. This work has been targeted to address unanswered questions about the sources and processes thought to account for the anomalous levels of mercury. Sources and transformations of mercury in natural ecosystems are poorly understood and a multi-disciplinary approach was required to understand the complex cycling of mercury. The multi-disciplinary group comprises biologists, geologists, chemists, limnologists, remote sensing and GIS experts.

The fieldwork was designed to collect samples for chemical analyses from a variety of media in a range of environments in and adjacent to the Park. The sampled media include: vegetation, soils, rocks, lake sediments, stream water, lake waters and ground water. Hg flux measurements were also made in order to characterize the exchange between vegetation, soils and water with the atmosphere. Project objectives include: (i) the characterization of Hg pools; (ii) the quantific-ation of fluxes between the various pools; and (iii) the description of various geochemical processes underlying the movement of mercury.

Over the first two years the project characterized the distribution of Hg in the various pools (media) and the spatial variation of mercury within the Park. The incorporation of the multidisciplinary data into a mass balance budget is still in progress, but initial calculations indicate the significance of atmospheric inputs. The mass balance work has also indicated several unexpected results, including: the importance of groundwater as a source of methyl mercury (MeHg) to lakes, and the accumulation and volatilization of mercury from vegetation. Based on the initial work, new areas of research have been incorporated into the final year of the project, including the analysis of microbiological and sedimentation processes in the mercury cycle.

The initial conclusions center around the importance of wetlands to the production and transport of methyl mercury, the contribution of soils as a mercury source, and the significance of mercury flux from various media. The research also indicates the possibility of using remote sensing to identify potential areas at risk for mercury bioaccumulation. The mass balance work will help to clarify the relative significance of inputs and outputs within the Kejimkujik ecosystem. The results from this project help resolve an important knowledge gap concerning the clarification of the role of atmospheric deposition, geology, chemical, photochemical, and biological processes in the mercury cycle. The data collected will allow for an enhanced knowledge base for site-specific risk assessments and to provide an improved framework for effective risk management strategies.

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Distinction between geogenic and anthropogenic metals in the environment
A historical perspective on the Rouyn-Noranda region

Savard¹, M.M., C., Bégin¹, M. Parent¹, J. Marion¹, A. Smirnov¹, X. Hou², Z. Sharp³

¹ Geological Survey of Canada-Québec, Ste-Foy, QC
² Institut National de la Recherche Scientifique (ETE), Ste-Foy, QC
³ Department of Earth and Planetary Sciences, U. of New Mexico, Albuquerque, NM

We have developed a high-resolution multi-tracer monitoring approach to distinguish between natural and anthropogenic accumulations of metals in the environment. We investigated the area of the Horne smelter in Rouyn-Noranda (Quebec), a copper smelting plant which has been emitting airborne metal particulates and toxic gases such as SO2 since it began operations in 1928. Our method is based on the assumption that the elemental contents and isotopic ratios of an individual tree ring reflect conditions, such as soil or air composition, that prevailed during the year it was formed. This is the approach we have been pursuing to help understand the cycling of metals in the environment (MITE Initiative).

Here we present the Cd and Pb concentrations, and H, C and Pb isotope ratios determined for tree ring series of 120 years. These natural and anthropogenic dendrogeochemical tracers were used to characterize 7 sites, among which 6 are distributed within a 116 km radius around the smelter, and one is located in the remote area of east Hudson Bay, 800 km from Rouyn-Noranda. For each site, we have also made detailed studies of the soil profiles and the dendroecological conditions. Our results on the natural tracers, H and C stable isotope ratios, indicate that SO2 generated an immediate diminution of photosynthetic activities at the onset of smelter operations. The natural tracers therefore describe the timing of chemical changes in the ambient atmosphere of the investigated trees. In contrast, the concentrations of anthropogenic tracers document the timing of changes in soil chemistry. Our results for Cd and Pb concentrations suggest that the root system incorporated smelter-emitted metals accumulated in the soil horizons only 15 to 20 years after the onset of smelter activities. The complementary Pb isotope tracers are indicating changing Pb sources over the same period. Abitibi sulphides processed throughout the smelter history had minimum 206Pb/207Pb values of 0.920, this represents the lowest end of the known range in North America and likely represents one end-member of the range for local smelter emissions. Our ongoing investigation of soil geochemistry suggests that geogenic local Pb is characterized by 206Pb/207Pb values around 1.228. Canadian and American Pb ratios in urban air are estimated to be 1.150 and 1.220, respectively. These values along with the soil data suggest that pre-smelter tree-rings contain both geogenic and airborne urban Pb, whereas the syn-smelter rings contain geogenic, urban, as well as smelter-emitted Pb.

The results of the present study demonstrate that simultaneous application of independent dendrogeochemical tracers help in understanding how pollutants affect the behaviour of trees. This approach also provides a high resolution historical perspective on the accumulation of metals in the environment, a very effective way to differentiate between their natural and anthropogenic sources, and a means to evaluate their relative contribution.

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Development of a 200-yr long ice-core record of atmospheric trace metal deposition in the Canadian Arctic: An overview of methodology and progress report.

Zheng^1, J. D. Fisher¹, C. Zdanowicz¹, E. Blake², G. Hall³, J. Vaive³ and G. Lawson^4
1 Terrain Sciences Division, Geological Survey of Canada, Ottawa, ON
² Icefield Instruments Inc., Whitehorse, YK
³ Mineral Resources Division, Geological Survey of Canada, Ottawa, ON
⁴ National Water Research Institute, Environment Canada, Burlington, ON

Growing concerns about long-range transport of atmospheric pollutants into the Arctic relate to adverse effects of certain pollutants (e.g., toxic metal species) on the health of Arctic ecosystems and human residents, and to trans-border pollution legislation issues. Ice cores drilled from ice caps can be used to develop archives of atmospheric pollution in the Arctic, allowing for modern depositional trends to be viewed in a long-term perspective. As part of the Geological Survey of Canada's Metals in the Environment (MITE) initiative, a 65-m long ice core was drilled in April 2000 on Devon Island (75 N; 82 W, 1860 m). The core is estimated to span a period extending back to ca 1800 AD, with annual to multi-annual temporal resolution. The ice core will be used to develop a modern to pre-industrial record of atmospheric trace metal deposition for the Canadian High Arctic.

The Devon Island core was drilled with a new titanium auger (diam. 8.2. cm) custom-designed to minimize metal contamination of the ice. Trace metals in polar snow are typically present at sub-ppb to low ppt levels. Hence, stringent quality-control procedures are needed to ensure that concentrations measured in ice cores truly reflect atmospheric deposition. A decontamination protocol was developed for the Devon Island core that involves stepwise removal of concentric ice layers with pre-cleaned titanium tools. The successive layers were analysed at the GSC by ICP-MS for a range of metals including Cd, Cu, Pb and Zn. Results show a rapid decrease in the concentration of all metals of interest between the outermost layers (1 cm) and inner cores. Metal levels in the inner 6-7 cm of cores show constant or near-constant values, indicating that any contamination is limited to the outermost layers. A comparison between inner core concentrations for Cu, Cd, Pb and Zn and published data from other polar snow and ice cores reveals a good agreement in the range of values observed. Our findings demonstrate that the new drill and the stepwise decontamination procedure allow for accurate measurement of ice-core trace metal concentrations that reflect true atmospheric deposition levels. Some typical metal concentrations found in test cores dating from the late 1960s to late 1970s are: 65-240 ppt Zn, 10-300 ppt Pb, 20-50 ppt Cu, and 1-5 ppt Cd. That some metals are only present at a few ppt in ice that formed during a decade of heavy industrial activity anticipates the difficulties of establishing meaningful trends over longer time periods.

Sampling of the Devon Island ice core is expected to be completed by the end of 2002. The 200-yr record of atmospheric trace metal deposition developed from the Devon Island core will be the first of its kind ever obtained in the Canadian High Arctic.

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