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Émilie Leclerc

 

Master student

Department of Chemistry, Université Laval

Alexandre-Vachon Building
1045 avenue de la Médecine
Université Laval
Quebec, Canada
G1V 0A6

418.656.2131 extension 405695
emilie.leclerc.8@ulaval.ca

 

 


 
 
 

Projet de recherche

Mobility of arsenic in lake sediments influenced by Giant Mine emissions, Northwest Territories

Introduction

In the 1940s, mining activity was the principal economic driver of the Northwest Territories. One of the biggest abandoned mines is the gold mine Giant, in the Yellowknife area. Extraction of gold from arsenopyrite generated arsenic trioxide between 1940 and 2004. This contamination went beyond the immediate mining sites via emissions to the atmosphere and subsequent deposition on soils and lakes. At present, the extent of this legacy is poorly known. Yellowknife is in the subarctic area, one of the most rapidly warming areas in the world. As climate warms, the permafrost melts and the decomposition rates for organic matter accelerate. This increases the load of dissolved organic matter, promotes greenhouse gas emissions and increases the mobility of contaminants in the water. In the context of pollution caused by mining activity, it is possible that some of the trapped emissions from the region's soils and lakes will be remobilized.

My project is part of the research program Sub-Arctic Metals Mobility Study (SAMMS) that aims to characterize the transport and behaviour of dissolved organic matter and the associated metals/metalloids in soils and aquatic systems.

My objectives are to determine the extent and history of arsenic contamination in lakes using the sediments as an environmental archive. Because arsenic is mobile in sediment, I will assess the mobility and its possible remobilization in water. The study of sediments and their water content (porewater) gives important information on the reactions that are happening now and can help to reconstruct what happened historically in the local environment.

Study sites

Eight headwater lakes were sampled 10 km apart from an 80 km transect northwest from Giant Mine, Yellowknife area (Northwest Territories). At each lake, four sediment cores were taken for dating, paleolimnology, organic carbon, inorganic sulfur, and porewater constituents. Sediment samples are taken by sectioning the sediment core while porewater samples are collected with an hydrophilic porous polymer tube.

Material and methods

The porewater samples can be directly analyzed by inductively coupled plasma mass spectrometry (ICP-MS) for metals and metalloids. Acid volatile sulfides are analyzed by ultraviolet-visible spectroscopy after extractions. Comparison of the concentrations profile obtained for different elements allows speculating on the reactions that occur in the sediment. Finally, I perform diagenetic modelling calculations to determine arsenic reaction rates and the fluxes. They allow to later assess the effect of diagenesis, in all the transformations that sediments undergo by chemical reactions, as well as the physical and biological processes that control the distribution of elements. This information is then used to discriminate between natural and anthropogenic arsenic sources, and to quantify its mobility in sediments and its probabilities of remobilization to lake water.

Expected results

It is expected that the maximal concentration of dissolved arsenic in lakes should decrease in function of the distance of the mine but should also coincide with the peak emissions generated during its years of activities. The significance of this project lies in obtaining relevant information on arsenic contamination in the Yellowknife area. In addition to arsenic, I will also analyze other elements, especially rare earth elements. They are of significant economic interest as they are essential for various technological applications. Moreover, their aquatic geochemistry is still unknown. Significant concentrations have been analyzed in the region; it is therefore a good opportunity to study these elements in the sampled sediments and porewaters.

 
 
Location of the research sites
 
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