Research Summaries 2002-2003> Sources Domain |
EdwardsWe will develop laboratory methods to: 1) determine gaseous Hg processes, and 2) characterize the relationship between metal/elemental concentrations and particle sizes for natural substrates and associated aerosols. A resuspension chamber method will be designed to determine aerosol-soil fractionation and chemical composition for various natural soils to create source profiles that can be used for source apportionment. Source profiles and Hg emission data obtained by laboratory studies will be used with particulate and exchange models to determine fluxes of Cd, Cu, Hg, Ni, Pb, and Zn. The characterization of source profiles and of natural fluxes of metals can be used with source apportionment/modelling techniques to determine source-receptor relationships needed for ERA. Return to 2002 Domain Research Projects
Lamoureux (top of page)The concentration of lead, nickel, copper, zinc and cadmium associated with atmospheric particulate matter of various sizes will be determined using both laser ablation and solution nebulisation as the sample introduction device for sample analysis using inductively coupled plasma mass spectrometry (ICP-MS). This will allow direct, simultaneous quantification of several metals (e.g., lead, copper, nickel, etc.), without sample pre-treatment in the case of laser ablation, as a function of particulate size. The isotope ratio of lead will also be determined and used as a potential indicator of the origin of metal emission in the region of Sudbury. The chemical nature (or speciation) of airborne metal species, as they exist in atmospheric particulate matter, will also continue to be investigated using synchrotron x-ray absorption fine structure (XAFS) spectroscopy. This will provide insight about the actual chemical nature (and hence their toxicity and chemical reactivity) of the airborne metal species of various sizes collected in the Sudbury region. This information is urgently needed for source apportionment assessment and for source identification. Return to 2002 Domain Research Projects
Carignan (top of page)Lake sediments are often used to reconstruct the history of metal deposition and to determine the relative importance of human vs. natural sources of pollution. However, chemical and biological processes occurring in lake sediments (early diagenesis) can influence the vertical distribution of trace elements, and compromise the use of sediment profiles as historical records of anthropogenic contamination. This study examines the chemical behaviour and determines the post-depositional mobility of trace elements (Hg, Cd, Cu, Zn, Ni, Pb, As) in recent lake sediments of unperturbed boreal Shield lakes exposed to high, medium and low levels of atmospheric pollution. Dated sediment cores and porewaters are analyzed for major and trace elements. The vertical redistribution of metals in sediments is quantified using diagenetic models. Measurements of stable Pb isotopes are used to quantify Pb sources to sediments and determine Pb availability to aquatic organisms. Techniques will be developed to improve the vertical resolution of pore water profiles and our understanding of diagenetic processes. The study will determine in which cases sedimentary metal profiles can be interpreted as historical records of trace metal pollution from human activities. Return to 2002 Domain Research Projects
Lu (top of page)This project focuses on applications of the new method developed by our group in year 2001-02 to chemical speciation of volatile metals associated with atmospheric particulate matter/aerosols and with suspended matter in wet precipitation. The new method combines a temperature-programmable thermal desorption process for separating metal species with ICP-MS for chemical detection. It has the following advantages: 1) no direct sample handling and no sample transfer, and ii) no addition of chemicals and reagents, hence no modification of chemical species present in the sample and sample matrix. This research can provide identification and quantification of metal species associated with atmospheric aerosols and suspended matter in wet precipitation. This information can be used to:
The above information is important in understanding the cycling of these metals in the environment and in assessing the risk of toxic metal species to ecological systems and to human health. Return to 2002 Domain Research Projects
Palace (top of page)This project is part of a larger ongoing study to examine the geochemical factors determining arsenic mobility in sediments that have been historically loaded with arsenic rich gold mine tailings. Balmer Lake, the study site, is a freshwater system in Northwestern Ontario that receives treated mine tailings from 2 active gold mines (Placer Dome and GoldCorp). The project is currently examining the role of nutrients, organic carbon and redox conditions on the remobilization of arsenic from sediments to the overlying water column and resident biota. Additionally, reclamation strategies utilizing microporous mineral matrices are being examined using a series of field enclosure (limnocorral) experiments. The MITE-RN funded portion of the project is designed to determine the potential for bacteria that reduce arsenic as part of their energy metabolism to contribute to arsenic mobilization from the sediment into the water column. Iron is the most important factor for binding arsenic in the sediments. Since the binding of arsenic is dependent on the redox state of iron, bacterial reduction of iron is also relevant and will constitute a major portion of these studies. Return to 2002 Domain Research Projects
Spiers (top of page)Accurate geochemical analysis of trace elements in aerosolic particles is still relatively difficult and non-routine because the analytical techniques are not readily available, not cost-effective or simple to use, or of sufficient sensitivity. Moreover, advanced particle analysis techniques such as laser ablation ICP-MS are inherently destructive; as are techniques requiring digestion of grains prior to nebulization into a plasma emission, mass spectroscopic or atomic absorption spectrometers. An advanced fine focus EMMA system was constructed to enable non-destructive chemical analysis of single grains, aerosol particles, aerosol and water filters in Phase I of this research project. Planned modifications to the instrument will improve grain manipulation capability to enable analysis of smaller particles (5-20 microns). Installation of an alternate rotating sample holder will also enable analysis of zonation, or variability, of aerosol load on any filter. Collaborative research initiatives with other members of MITE-RN will include analysis of samples collected with cascade samplers and low volume samplers installed at appropriate sites within the Sudbury Footprint, with samplers being analyzed with the EMMA before shipping to Halifax for additional analyses. The quantitative elemental data obtained will be complementary to the speciation information obtained on selected samples using EXAFS (Lamoureux, Project A2). Non-destructive analysis of mineral grains separated from soils, as well as selected smelter dusts, before and after the weathering simulation studies will provide information on congruent or incongruent dissolution, and on the possible presence of reprecipitation crystals of short-range order (Hendershot, new project).Aerosol/dust samples will be collected on a regular schedule within the Sudbury region using sampling equipment (snow and precipitation collectors) installed in a grid pattern defined by the historical metal enrichment patters in surface soils. The resultant data will enable quantification of composition, mineralogy and mass of modern particle fallout. The chemical composition may provide an insight into particle provenance. Particle emissions history is being provided by related studies examining relict smelter particles in soils, sediments and peat lands of the Sudbury smelter footprint. Return to 2002 Domain Research Projects
Gould (top of page)The major goal is to determine if bacterial activity, such as iron and manganese reduction, can mobilize metals and cause their redistribution both within the sediment profile and back into the water column. If metals are solubilized by bacterial reductive activity, then the mechanisms of metal transport and re-deposition will also be investigated. The potential effect of metal remobilization into the water column will be assessed through toxicity testing (e.g., Daphnia magna). While remobilization of metal from sediment to water has the potential to be a hazard, this will only occur if the dissolved metals are in a form which allows them to be bioavailable and toxic. Direct toxicity testing will help to understand the degree of hazard associated with remobilized metals. A series of lake sediment cores will be taken from one field site (Lac de la Pépinière) in the vicinity of the Horne smelter in Rouyn-Noranda, Quebec. They will be used in a series of laboratory microcosm experiments to simulate natural conditions and investigate the resultant metal transformations through various tracer studies. An essential experiment will be to expose the cores to varying redox conditions (aerobic and anaerobic cycles) to stimulate seasonal changes in oxygen penetration. In a separate series of experiments, different tracer metals with more than one stable isotope (e.g., Fe, Cu, Ni) will be added to the cores. Another set of experiments will involve adding to the cores an organic source to serve as both electron donor and carbon source. For each series of experiments, the cores will be incubated for varying lengths of time under anaerobic conditions and then destructively sampled for analysis of metal distributions and enumeration of key groups of bacteria. Where appropriate, toxicity testing will be performed on the overlying waters. Return to 2002 Domain Research Projects
Percival (top of page)The texture, bulk properties (e.g., density, moisture content, particle size distribution) and chemical characteristics of surficial materials are significantly influenced by the mineralogy and depositional and post-depositional processes (e.g., compaction, diagenesis and pedogenesis) that affect them. Detailed mineralogical analyses can identify the mineral and non-mineral phases that comprise a soil or sediment. Some of these phases may be authigenic and hence indicate early pedogenetic (or diagenetic) processes, whereas others form distinctive morphology due to their origin as atmospherically-transported particulates. The six soil sites in Sudbury and Rouyn-Noranda have been developed on glacial sediments and bedrock that are rich in trace metals. These sites are currently instrumented (lysimeters) and under investigation in Project B1, "Post-depositional mobility of trace metals in boreal forest ecosystems" and will be the focus of a complementary study by Hendershot examining rates of trace metal release due to weathering. An additional site will be studied at Plastic Lake, the site of project B5, "Metal budgets of lakes and catchments on Precambrian Shield: compartment sizes and fluxes between compartments". Return to 2002 Domain Research Projects
Hendershot (top of page)The soils in areas near Cu and Zn mines are often developed on glacial sediments and bedrock that are rich in trace metals. Since metals released from this natural source could easily be confused with metals associated with anthropogenic pollution, it is important to quantify the magnitude of this source. With the collaboration of researchers in the GSC (Percival) we will identify minerals or polymineralic rock fragments (sand or silt sized) that would be a source of trace metals as the material weathers. The materials thought a priori to be the most likely to release trace metals were separated for use in laboratory weathering experiments. The data obtained will be used to calibrate existing mineral weathering models that will then be used to make estimates of annual release rates of trace metals. The mineral grains, in the unweathered and weathered states, will be examined by Graeme Spiers, and perhaps Marc Lamoureux, to determine the degree of crystal breakdown and the accumulation of weathering products (which may include re-deposited trace metals) on the grain surfaces. |