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.