Origin and Fate of Contaminants in the Environment
Location: University of Toronto
Advisors: Drs. Barbara Sherwood Lollar and Bridget Bergquist (Toronto)
Graduate student (PhD) sought for project on using novel isotope techniques to track the origin and fate of environmental contaminants in the environment – particularly looking at the interface between groundwater—surface water and sediments. Background in earth sciences, chemistry or microbiology an asset. Laboratory and field based projects available all of which involve collaboration with multiple MAGNET nodes and industry partners.
Tracking Atmospheric Mercury Sources by Isotopic Fingerprinting
Location: University of Toronto
Advisors: Drs. Bridget Bergquist and Barbara Sherwood Lollar (Toronto)
The long-term goal of the Bergquist research program is to use Hg isotopes in improve our understanding of the Hg biogeochemical cycle and to develop Hg isotopes as a proxy of past environmental changes. Mercury is a globally distributed metal that bioaccumulates in aquatic food webs leading to dangerous exposure to humans and wildlife. Mercury is often emitted the atmosphere in its reduced form, gaseous elemental Hg (GEM), by both primary natural (e.g. volcanic, hydrothermal) and anthropogenic sources (e.g. artisanal small scale gold mining, coal burning) and by secondary re-emissions from the ocean and soils. GEM is relatively stable and has a long residence time (~0.5 to 1 yr), which allows it to be distributed globally. Despite decades of research, many knowledge gaps hinder our understanding of both the modern and past Hg cycle and make it challenging to predict how changes in emissions and climate will affect the Hg cycle along with limiting our ability to utilize Hg and Hg isotopes as proxies of past environmental change. For example a recent assessment of GEM exchange to and from terrestrial surfaces highlighted that very large uncertainties still exist over the controls and fluxes of GEM especially in forested ecosystems to the point that hinders our ability to determine whether some ecosystems are net sources or sinks of Hg. Another area that is hotly debated is the relative contribution of different sources of Hg to the atmosphere such as coal combustion and artisanal and small scale gold mining at local, regional and global scales.
While mercury isotopic fingerprinting is increasingly recognized as a powerful tool for tracking sources of mercury, its application to atmospheric source tracking is hampered by the difficulty to collect sufficient amounts of mercury from air for reliable isotopic quantification and/or by the possibility of imposing inconsistent levels of fractionation during sampling. Recently, a new highly precise passive air sampler for GEM concentrations was developed (McLagan et al., 2016). This low-cost sampler can collect GEM from air for periods of at least one year, and can collect sufficient mercury for isotopic analysis even at typical background concentrations. The U of Toronto Trace Metal and Metal Isotope Laboratory is seeking a PhD to lay the groundwork for confidently applying the passive Hg sampling technique for atmospheric source identification.
- Perform a number of laboratory and field experiments to confirm the extent and reproducibility of the mercury isotope composition and potential fractionation occurring during passive sampling.
- Conduct a reconnaissance of the spatial and temporal variability of the isotopic signature of mercury in the atmosphere.
- Deploy the passive sampler along transects of increasing distance from known sources of gaseous mercury to establish the extent to which a source’s possible unique isotopic fingerprint fades into the regional background signal by dilution.
Honey Bees as Bioindicators of Environmental Pollution
Location: University of British Columbia
Advisors: Drs. Dominique Weis and Marg Amini (UBC)
Natural variation of radiogenic and metal stable isotopes is successfully applied in Earth sciences as a tracer of geological processes and for identifying the source and fate of contaminants in the environment. The development of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) over the last two decades has revolutionized this field by enabling precise analyses of such isotopes in a wide range of geological, environmental and biological materials.
This PhD project applies these proven techniques to biological systems, focusing specifically on honey from beehives in the greater Vancouver area, in collaboration with a local non-profit organization (Hives for Humanity). Honey bees are social and live in colonies numbering in the thousands. Bees are major pollinators of flowers and key for the reproduction of plants. An average bee works in an area of 2 km diameter, and as such, the honey that they produce is a sampler of their environment and varies on a relatively small scale. This study will involve the elemental analysis of trace metals (Cd, Cu, Zn, Pb among others) and isotopes (Pb, Fe, Cu, Zn) in the honeys at the Pacific Centre for Isotopic and Geochemical Research (UBC).
Pb isotopic compositions represent one of the best tools to trace the source of pollutants. Pb is volatile and has been distributed in the environment at a global scale due to its use as anti-knock agent in gasoline until the 1990’s. The accumulation of Pb can be found all the way to the Greenland and Antarctic ice sheets. A preliminary study shows that the variations in both concentrations and isotopic compositions of Pb observed among these honeys over a sampling period of three years are directly correlated with their location (i.e., urban vs. rural).
This PhD project will continue and expand the study of Fe, Cu and Zn isotopes to model isotope discrimination in the soil-plant system, through plant physiology and finally during the metabolism of these metals by the bees and their incorporation into the honey. In addition, honey from new locations in the province (and close to potential specific sources of pollutants, such as ports, paper mills, etc.) will be collected to extend the geographical coverage and lengthen the sampling period. Other products of bee activity will also be analyzed.
Lastly, there is potential scope in this project to explore the incorporation of metals and their isotopes along the food chain up into the human body. In this project, honey may be used as an example to study reaction pathways of metal isotopes during biological and physiological processes from plant uptake to metabolic turnover.
Impact on greenhouse gas (GHG) emissions, soil carbon and nutrient stocks following Beneficial Management Practices (BMPs) for agro-drainage systems
Location: University of Ottawa
Advisors: Dr. Ian Clark (University of Ottawa) and Dr. David Lapen (Agriculture and Agri-food Canada)
This project will examine soil/sediment GHG (e.g., nitrous oxide, carbon dioxide, methane) emission/transformation processes and carbon stores associated with a suite of agricultural BMPs (e.g., riparian buffers, drainage management/effluent treatment, manure/biosolid application practices, cover crops, and constructed wetlands), and critically important natural habitat in agriculturally intensive agro-ecosystems (e.g., forested plots, treelines, wetlands). In this study the physical-chemical processes controlling nutrient cycling and GHG emissions from soil/sediments will be examined to explore the nature and volatility of soil carbon and nitrogen under a variety of plausible land practice/environmental scenarios expressed at the soil, field, and/or landscape level at a research site with controlled tile drain systems (Cicek et al., 2013.
The benefits of nitrogen amendments using animal manure, present as organic N and ammonium-N (Beauchamp, 1986) is compromised by its relatively rapid mineralization, nitrification and transport from soils to drainage waters. A variety of reactions can occur in agricultural soils, resulting in the conversion of N to other forms (Butterbach-Bahl et al., 2013). Nitrogen cycling and fate of nitrogen applications, both from manure and granular synthetic nitrogen, a key component of BMP development and nutrient management strategies, is closely linked with C and N emissions and effluent impacts on drainage systems. Mitigation strategies range from integrated bioreactor systems to passive riparian zone management. Promising research has been directed towards establishing the variations in emissions under both controlled and uncontrolled drainage conditions, focused primarily on a determination of N2O fluxes at the soil-air interface, the d15N of N2O in these soil gases, d15N in soil, and variable concentrations of NO3– in water. Key will be to focus on the nitrogen outputs from CTD and UTD interventions into the active and passive mitigation systems to establish a comparative framework to bridge the gap between sources of nitrogen, N2O fluxes, and NO3–, NH4+ loadings on groundwater and surface water.
The objectives of this research are to (i) characterize C and N cycling, storage and emissions in an established agrosystem of controlled and uncontrolled drainage with integrated bioreactor system, and (ii) quantify the functionality of the bioreactors with laboratory and predictive modeling approaches.
Field work will take place at the AAFC research site in eastern Ontario. The candidate will lead a field team installing and sampling all matrices (soil, soil air, soil water, groundwater, drain tile discharge and bioreactor zones) through the integrated field to reactor/receptor system for analysis of stable and radioisotopes (T and 14C). Laboratory aspects carried out in the Advanced Research Complex at the University of Ottawa which hosts the extensive geoscience laboratories for stable isotopes, geochemistry and accelerator mass spectrometry for radiocarbon and other radioisotopes (http://www.ams.uottawa.ca/).
Beauchamp, E.G., 1986. Availability of nitrogen from three manures to corn in the field. Can. J. Soil Sci. 66(4), 713-720.
Butterbach-Bahl, K., Baggs, E.M., Dannenmann, M., Kiese, R. and Zechmeister-Boltenstern, S., 2013. Nitrous oxide emissions from soils: how well do we understand the processes and their controls? Phil. Trans. R. Soc. B 368(1621), 20130122.
Cicek H, Sunohara M, Wilkes G, McNairn H, Pick F, Topp E, Lapen DR (2010) Using vegetation indices from satellite remote sensing to assess corn and soybean response to controlled tile drainage. Agr Water Manage 98(2): 261-270.
Measuring mineral dissolution kinetics using newly developed flow-through instrumentation
Location: University of British Columbia
Advisors: Drs. Roger François and Ulrich Mayer (University of British Columbia)
As part of a recent doctoral thesis (De Baere, 2016) a new, purpose-built flow-through leaching module has been developed. What differentiates this dissolution technique from more conventional techniques (e.g. mixed flow reactors) is the small sample size (~ milligrams) and small volume of the flow-through reactor (~ microliters). This results in (1) the much faster attainment of steady state eluent concentration when trying to measure mineral dissolution rates and (2) the ability to record effluent composition at high temporal resolution (when connected online to an ICP-MS in time-resolved analysis mode) documenting transient events. To date, the flow-through module has been applied as a tool to:
- establish much more rapidly compared to conventional methods pure mineral dissolution rate parameters (e.g. olivine: De Baere et al., 2015).
- document dissolution regimes (transport versus surface-controlled dissolution, e.g. calcite: De Baere et al., 2016).
- document transient dissolution events. Examples include monitoring labile vs. recalcitrant cation release (Carroll et al., in preparation), exfoliation events (De Baere et al., 2015).
- identify mineral phases in mine waste rock hosting metals of potential environmental concern (De Baere, 2016).
The PDF will be given the opportunity to formulate the key research question to be pursued as part of this 1-year PDF appointment. In addition, the PDF will be strongly encouraged to seek out additional external funding to help carry out the proposed research.
Two suggested projects include:
(1) Addressing a long-standing mineral dissolution rate conundrum: “surface area normalization”. This project would relate mineral nanoscale imaging of surface topography to bulk dissolution rate measurements by combining data obtained from the flow-through dissolution module with atomic force microscopy (access can be obtained to fluid-cell Atomic Force Microscopy at 4D Labs in Burnaby). Atomic Force Microscopy has revealed that mineral dissolution rates depend on the density of mineral surface features, such as steps, kinks and screw dislocations, which act as active surface dissolution sites. Thus, a paradigm shift is required to effectively model mineral dissolution. The large disparity of dissolution rate constants that have been measured experimentally thus far is now largely attributed to our inability to normalize dissolution rates to the “active” surface area reflecting surface topography. This project will explore replacing dissolution rate constants by spectra of rate constants which capture the variability in the density of active surface sites. If the density and types of active surface sites are amenable to predictive modeling and anchored to a bulk mineral property that can be measured to determine ab-initio conditions, this information could then be applied to any condition in the laboratory or in the field.
(2) The potential for leaching of mine tailings deposited in a lake: The breach of the Mount Polley mine tailings impoundment in August 2014 resulted in the deposition of a large volume of fine tailings into the bottom of Quesnel Lake. While the mineralogy of the tailings does not suggest the potential for acid generation and metal leaching, the biogeochemical conditions at the lake bottom water interface might play a role in determining the reactivity of the deposited material over time. A research project is underway to measure the chemical and biological characteristics of the deposited material on the bottom of Quesnel Lake since these will allow some prediction of whether conditions will promote or prevent metal release. To increase knowledge of the reactivity of these tailings under the range of conditions expected in the lake bottom the flow-through leaching module will be used. The apparatus will measure the concentrations of metals or other chemicals released when tailings samples are exposed to a range of conditions, such as with or without oxygen, in the presence or absence of microorganisms reflective of the conditions highlighted in the field survey. Metals known to be present in the tailings at levels above background include copper and arsenic.
Carroll, K. et al. (2017) Targeted mineral dissolution for optimization of carbon sequestration in mine waste. In preparation.
De Baere, B., Molins, S., Mayer, U.K. (2016) Determination of mineral dissolution regimes using flow-through time-resolved analysis (FT-TRA) and numerical simulation. Chemical Geology 430: 1-12.
De Baere, B. (2016) Investigating mineral dissolution kinetics by flow-through time-resolved analysis (FT-TRA). PhD thesis, University of British Columbia.
De Baere, B., François, F., Mayer, U.K. (2015) Mineral dissolution rate and dissolution stoichiometry by flow-through time-resolved analysis (FT-TRA): a case study using forsterite. Chemical Geology 413: 107-118.
The effect of organic matrices on the accuracy and precision of trace metal analyses by plasma source instruments
Location: University of British Columbia
Advisors: Dr. Dominique Weis (University of British Columbia) and Dr. Bridget Bergquist (University of Toronto)
The analyses of trace metals and their isotopes by plasma source mass spectrometry is often burdened with uncertainties due to instrumental mass bias. An important factor affecting elemental and isotope fractionation by instrumental mass bias is the matrix the analyte of interest is contained in. Sample matrices have been shown to severely affect sample introduction, instrumental sensitivity, mass resolution and mass bias (e.g., Andren et al., 2004; Agatemor and Beauchemin, 2007). In particular, organic substances appear to cause unstable signals and measurement drift.
To minimize these effects, samples commonly undergo a chemical purification procedure that largely separates the analyte from the sample matrix. However, the separation of the analyte is often incomplete, and can lead to the loss of the analyte itself as well as to the addition of residues from the extractive phases. Also, biological materials and transitional metals are not stable in acidic or nitric environments; in contrast, samples such as blood and urine, and elements like Se, Cd and Hg are more stable in organic solvents and base solutions. While the effect of inorganic and acidic sample matrices has been widely studied (e.g., Stewart and Olesik, 1998; Pietruszka et al., 2006), little is known about measurement conditions for basic, organic solvents (Schoenberg and von Blanckenburg, 2005; Pietruszka and Rezenik, 2008).
The goal of this study is to systematically investigate the effects of organic compounds in analyte solutions for ICP-MS analyses and to optimize instrumental parameters to increase measurement precision and accuracy. The successful post-doctoral candidate will measure synthetic metal standard solutions and biological reference materials treated with commonly used organic solvents (compared to conventional acidic counterparts) under different instrumental settings at the Pacific Centre for Isotopic and Geochemical Research (UBC) and the Trace Metal and Metal Isotope Laboratory (University of Toronto). Matrix effects will be monitored for instrumental mass bias, signal drift and molecular interferences potentially caused by organic compounds.
This study will help determine optimum sample preparation and measurement conditions for the analyses of trace metals in biological samples and samples with organic matrices. It will also lay the groundwork for the establishment of online chromatographic separation and analyses by connecting IC/HPLC systems to ICP-MS (Carignan et al., 2001). In addition, the results will have important implications for the general understanding of matrix effects on instrumental mass bias in plasma mass spectrometry.
Agatemor C. and Beauchemin D., 2007, Analytica Chimica Acta 706, 66-83.
Andren H., Rodushkin I., Sternberg A., Malinovsky D., and Baxter D. C., 2004, Journal of Analytical and Atomic Spectrometry, 19, 1217-1224.
Carignan J., Hild P., Mevelle G., Morel J., and Yegicheyan D., 2001, Geostandards Newsletter, 25 2-3, 187-198.
Pietruszka A. J., Walker R. J., and Candela P. A., 2006, Chemical Geology, 225, 121-136.
Pietruszka A. J. and Reznik A. D., 2008, International Journal of Mass Spectrometry, 270, 23-30.
Stewart I. I. and Olesik J. W., 1998, Journal of Analytical and Atomic Spectrometry, 13, 843-854.
Schoenberg R. and von Blanckenburg F., 2005, International Journal of Mass Spectrometry, 242, 257-272.
Optimizing Fe isotope analyses by ICP-MS
Location: University of British Columbia
Advisors: Dr. Dominique Weis (University of British Columbia) and Dr. Ye Zhao (Nu Instruments)
Iron (Fe) is the fourth most abundant element in the Earth’s crust and is ubiquitous in geologic materials. It is of great interest to isotope geochemists and biogeochemists due to its vital role in global biogeochemical cycling (e.g., Beard et al., 1999; 2003) and for its newfound application in fingerprinting igneous and ore-forming processes (e.g., Heimann et al., 2008). While the Fe isotope literature grows continuously, even the most recent research demonstrates that there remain outstanding questions regarding the mechanisms that control stable Fe isotope fractionation in nature, particularly in magmatic-hydrothermal settings. Naturally occurring mass-dependent Fe isotope fractionation is relatively small, requiring especially accurate and precise measurements. This is of particular importance within high-temperature systems typical of magmatic environments and related economically significant deposits since fractionation scales with temperature by 1/T2.
Accurate analysis of such samples was nearly impossible until the advent of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) just two decades ago, and continued improvement of MC-ICP-MS is responsible for the realization of measureable Fe isotope fractionation in igneous rocks (Poitrasson & Freydier, 2005; Heimann et al., 2008). Since then, studies have demonstrated that the Fe isotope signatures of whole rocks and mineral separates can reflect fractional crystallization, fluid exsolution, redox changes, bonding environment, temperature gradients, and sub-solidus re-equilibration. They have also begun to show that it is possible to quantitatively assess the effects of each of these components.
Compared to traditional thermal ionisation mass spectrometry (TIMS), the MC-ICP-MS has higher ionization efficiency, allows higher sample throughput and better measurement precision. The main challenge when using MC-ICP-MS for Fe measurements is the formation of argon (Ar) complex isobars that interfere with all four stable Fe isotopes: 54Fe, 56Fe, 57Fe, 58Fe. If these isobaric interferences are not taken into account, accurate quantification of natural Fe isotopic will not be possible. The traditional approach to overcome this is to use the high-resolution or pseudo-resolution mode to resolve or partially resolve the isobaric interferences from the analytes. This is achieved by narrowing the source slit, which significantly sacrifices the ion transmission, and as a result a much higher sample concentration is required for Fe analysis.
The new Sapphire MC-ICP-MS, with its unique collision/reaction cell function, will remove the Ar interferences and make highly accurate and precise measurements of all four Fe isotopes attainable in the low resolution mode, greatly reducing the sample size limitation. The successful postdoctoral candidate will perform analyses by using the Nu Plasma 1700, Nu Plasma II and the Sapphire to compare the traditional Fe isotope measurement protocol with the new one. This project will serve as validation and promotion for the new Sapphire collision/reaction cell MC-ICP-MS and may have profound implications for the way in which we measure stable Fe isotopes in igneous and economic geochemistry.
The successful candidate of this one-year postdoctoral project will be based at the Pacific Centre for Isotopic and Geochemical Research, University of British Columbia and utilise the clean labs and the Nu Plasma 1700 and Nu Plasma II for initial testing of the measurements of the Fe standards/samples, and visit the Nu factory to analyse these on the prototype Sapphire instrument.
Beard B.L., C.M. Johnson, L. Cox, H. Sun, K.H. Nealson, and C. Aguilar (1999), Iron isotope biosignatures. Science, 285, 1889-1892.
Beard B.L., C.M. Johnson, J.L. Skulan, K.H. Nealson, L. Cox, and H. Sun (2003), Application of Fe isotopes to tracing the geochemical and biological cycling of Fe. Chem. Geol., 195, 87-117.
Heimann A., B.L. Beard, and C.M. Johnson (2008), The role of volatile exsolution and sub-solidus fluid/rock interactions in producing high 56Fe/54Fe ratios in siliceous igneous rocks. Geochim. Cosmochim. Acta, 72, 4379-4396, doi:10.1016/j.gca.2008.06.009.
Poitrasson, F., and R. Freydier (2005), Heavy iron isotope composition of granites determined by high resolution MC-ICP-MS. Chem. Geol., 222, 132-147, doi:10.1016/j.chemgeo.2005.07.005.