NWT RESEARCH DATABASE

Regions: North Slave Region

Tags: contaminants, site remediation, water quality, sediment chemistry, arsenic, hydrology, metals, hydrocarbon

Objective(s): To develop tools to assess risks associated with legacy industrial developments in a northern setting by investigating contaminants from the Giant Mine near Yellowknife NT.

Project Description: The research team propose to develop tools to assess risks associated with legacy industrial developments in a northern setting. The team will investigate contaminants from the Giant Mine near Yellowknife Northwest Territories (NT), which operated between 1948 and 2004, producing a legacy of contaminants including arsenic, antimony, hydrocarbons, mercury, and others. This remediation strategy applies to the Giant Mine property, so this research will develop new tools to inform the government of the NT and other regulators on how to manage the land and water in areas surrounding the Mine property, as they are within the limits of NT’s largest population center. Specifically, the research team will: 1) characterize metals (focusing on arsenic, antimony, and mercury), and hydrocarbons released from the mining operations to lake waters and lake sediment cores to quantify their releases and determine current and historical chemical exposures to natural systems; 2) use fossilized invertebrate and algal assemblages (well-known response variables used in contemporary impact assessments) to assess ecosystem responses to pollutants, which will be analyzed in radiometrically dated lake sediment cores; and 3) develop microbiological tools to assess microbially mediated mercury transformations which affect methyl mercury ‘hotspots’ near these legacy industrial sites. Subtheme 1: Characterizing the legacy contaminants from Giant Mine and Con Mine in sediment cores by paleoecotoxicology: The research team will use high-resolution lake sediment cores selected from lakes spanning a 50 km radius of Giant Mine to track the history of environmental pollution resulting from mining activities, including arsenic, which is expected to be an important tracer of development at the mine, but also polycyclic aromatic hydrocarbons (PAHs) and other metals like antimony, lead and mercury that have received less attention to date, yet represent important legacy contaminants from Giant Mine. In addition to characterizing emissions from Giant Mine in archived sediment profiles, the research team will also address how biological assemblages in these same archives have changed as a result of pollution from the mine, using diatom and cryophyte indicators in the same cores that have been used widely in pollution studies as well as other key indicators that are often used in ecotoxicology studies to assess metal and hydrocarbon pollutants. Sediment cores will be collected and analyzed using paleolimnological techniques that the research team has established over decades. Sediment profiles are dated using well established radioisotope techniques (210Pb, 137Cs, 226Ra, 7Be). Activity profiles will be measured in sediment cores to calculate rates of sediment burial, mixing depth, and sediment redistribution. Subtheme 2: Analysis of mercury methylation hotspots near Giant Mine: Mercury (Hg) is a priority contaminant that, in its methylated form, is a toxic substance that persists in the environment and is biomagnified through aquatic food webs. Once in the environment, mercury toxicity and bioaccumulation depend on in-situ synthesis of monomethylmercury (MMHg). Processes that directly or indirectly affect MMHg production modulate the impact of Hg contamination. The research team will investigate the environmental controls on MMHg cycling in lakes around Yellowknife and test whether mining operations contribute to the development of methylation hotspots. Lake sediments, soils, and waters in the area near Yellowknife are enriched in arsenic due to the lack of pollution controls during the early years of gold mining as well as the naturally high arsenic associated with gold mineralization. The recent research on samples from the Giant mine property has shown that natural and anthropogenic (roaster-generated) arsenic can be distinguished in soils and sediments using microanalytical mineralogical techniques. There is evidence that arsenic sulfide may form in anoxic sediments, attenuating dissolved arsenic and reducing the bioavailability of arsenic. The results of this research will contribute to improved risk assessment and remediation design. Sediment-pore water profiles from the peepers and adjacent cores will indicate whether arsenic is being released from sediments and diffusing upward into the overlying lake water. This is thought to be one of the most important mechanisms for arsenic enrichment in groundwater, both in mine-impacted sediments and arsenic-contaminated aquifers in south Asia. However, if sulfate-reducing bacteria are present, arsenic sulfide such as realgar may immobilize the arsenic and reduce bioavailability. The results will also be published in the primary literature, so that all stakeholders within and outside of Canada will have access to the findings. The government partners will be part of this investigation and the results will be considered in the development of guidelines and procedures for management of contaminants in a changing northern climate. The research team will ensure that the results are presented in public meetings (e.g. Water Strategy meetings (NT), local stakeholder meetings), in poster format, and in annual community reports as part of the communications plan of this project. The results are communicated regularly to the press via television, radio and printed news. The fieldwork for this study will be conducted from March 1, 2017 to August 30, 2017.