Could microbes help remediate abandoned gold mines?

Published: June 3rd 2019
Photo: Saint Mary’s University

Mines operating in Canada today adhere to rigorous environmental regulations and strive to minimize the impact of their operations on the environment.  But in the 1800s, before such legislation was in place, valuable minerals were extracted from ore using chemicals or concentrations of those chemicals that would not be permitted today.  For example, in Nova Scotia as elsewhere, liquid mercury was historically used to separate gold particles from the crushed ore.   The leftover material, called tailings, can contain mercury and arsenic that exceed acceptable standards.

The Government of Nova Scotia may undertake remediation efforts on some of the province’s legacy (abandoned) gold mines in the future.  A potential new tool may be added to the remediation efforts: genomics.

Genome Atlantic is partnering with Saint Mary’s University researcher Dr. Linda Campbell to study biological alternatives to the age-old problem of remediating legacy gold mine tailings.

Dr. Campbell, a noted environmental containment specialist, will explore whether microbes found in and around the lakes and wetlands impacted by 100-year old tailings could be the key to reducing toxic levels of mercury and arsenic. (The idea being that some microbes are natural remediation (clean-up) specialists in that they can detoxify heavy metals like arsenic and mercury.) This summer she and her team are undertaking a proof of concept pilot-scale investigation through Genome Atlantic’s Genomics Opportunity Review Program (GORP), with additional support from the Nova Scotia Department of Energy and Mines.

“In order to be able to develop effective, feasible and cost-manageable remediation approaches for freshwater sites, we need information and data to support the decision-making process,” said Dr. Campbell.

She explained that while extensive work has been done to develop a variety of ways to remediate ground and saltwater contamination, the impact of historical gold mine tailings on freshwater ecosystems is not as well understood.

Principally occurring in eastern mainland Nova Scotia, there are around 360 historic, abandoned mine sites that were established between the late 1860s and the 1940s.

Due to a combination of the province’s naturally occurring arsenic-laced geology along with historic gold processing practices that used mercury, levels of these toxic substances can be high in tailings.

Dr. Campbell explained, “freshwater sites have key chemical and biological differences, which means a remediation approach which works for terrestrial settings cannot be applied to freshwater settings.”

She predicted, “Our work investigating the metagenomic makeup of microbial communities in aquatic freshwater sediments will go a long way towards bridging this problematic data gap and supporting the necessary evidence-based decision making.”

The Nova Scotia government commissioned site characterization work this fiscal year at two large legacy gold mine tailing sites: at Montague, a rural community near Dartmouth, and at Goldenville near Sherbrooke. Based on the results, the province may soon be hunting for innovative remediation strategies.

Dr. Campbell’s inter-disciplinary team – Landon Getz, a PhD candidate with Dalhousie University’s Department of Microbiology and Immunology, who is studying bacterial genomics, and Dr. Josh Kurek, a Mount Allison University scientist who reconstructs past environments from physical, chemical, and biological evidence contained in lake sediments – are testing whether sediment metagenomics can provide needed information to help formulate a new remediation approach.

Metagenomics is the genetic analysis of genomes in an environmental sample that enables identification of the microbes or bacteria within. Campbell’s team will use this technique to analyze the surface sediment in specific contaminated and non-contaminated sites to find out what microbes are there and assess what their presence indicates about the state of the freshwater environments they inhabit.

It is known that some microbial communities can help reduce arsenic and mercury levels in their surroundings. Dr. Campbell explained, “some types of bacteria, especially iron and sulfur reducing species, can increase the bioavailability of arsenic and mercury to biological organisms, while other types can limit bioavailability. As a result, microbial approaches hold much promise for managing and limiting contaminant transfer to living organisms, including humans and wildlife. Before we can develop remediation strategies and remediation frameworks using those approaches, we need to better understand the microbiomes existing in those sites.”

Equally important, she said, is understanding “the makeup of microbial communities in healthy, unimpacted wetland sites to provide us with an approximate benchmark to consider while developing future remediation strategy frameworks.”

Consequently, environmental samples will be taken from three freshwater sites directly impacted by contaminated historical tailing materials from legacy gold mine sites plus two reference sites which have not been impacted by gold mine tailings. Those are all in the Halifax Regional Municipality, enabling rapid sampling and processing of the samples in the laboratory.

If all goes to plan, the resulting dataset this summer will pave the way for further and more long-term research into this relatively unexplored route to remediation.

“The province is always interested in pioneering new and innovative solutions that can be applied here, and around the world,” said Nova Scotia Energy and Mines Hydrogeologist Gavin Kennedy. “The work of Genome Atlantic and Saint Mary’s University is exciting and has the potential to change the way legacy gold mine sites are managed in the future.”