Sat. Apr 20th, 2024

Des lacs de N.-É. contaminated by old gold mines

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A sign posted in a former mining area in Dartmouth , Nova Scotia.

Radio-Canada

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Only one gold mine remains in Nova Scotia, but the historic era of gold mining has left behind a lot of contamination which continues. In a lake in Dartmouth, Nova Scotia, the situation is made worse by warming temperatures.

After a certain number of years, we should expect some level of recovery of the ecosystem, says Branaavan Sivarajah, specialist in the #x27;environment. But our study suggests that ecosystem recovery takes much longer.

He and other researchers dated and measured contaminants in the sediments of five Nova Scotia lakes that are within three regions where gold mining was taking place.< /p>Open in full screen mode

An image captured by drone of the site of the former Montague gold mine.

Their study, published in the journal FACETS, found that sedimentary metal concentrations have not returned to background values ​​even 80 years after the end of the industry that mined gold without worrying about the environment.

This suggests that complete geochemical recovery may not be a realistic goal in severely polluted lakes, the study reports.

Scientists took core samples from the lake bed and, using radiometric dating, were able to trace the levels of arsenic, mercury and other metalloids before, during and after extraction of the x27;gold.

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They visited four lakes, which were downstream of the mining operations and received mine tailings.

Lake Charles, Lake Thomas and the pond Muddy in Dartmouth and Gegogan Lake in Guysborough. They also took samples from Loon Lake in Dartmouth, which was upstream and did not receive any residue. It was used for comparison purposes.

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Mount Allison University professor Joshua Kurek takes a core sample at Dartmouth as part of research into contaminants from gold mines.

Mine tailings pollutant is a sand-like substance that remains after rock containing arsenic and gold has been crushed and spread on liquid mercury to bring out the gold. The residue from the process is therefore very toxic.

As expected, the concentration of toxins has decreased since mining stopped in most cases. But there were two exceptions.

The sediments of Gegogan Lake, downstream of Goldenville, contain mercury concentrations as high as during the peak period of #x27;mining. Researchers believe that tailings released into the lake still contain high levels of this chemical.

The situation is worse in Lake Charles. Now located in an urban area, the lake received tailings from the gold mining of the Montague mine in Dartmouth.

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This site where the Montague Gold Mines gold mine was located was still scheduled to be decontaminated in 2022.

Arsenic levels in Lake Charles have in fact has increased since 2010.

Branaavan Sivarajah says low oxygen levels caused by global warming likely triggered a chemical reaction that breaks down arsenic binding compounds.

Algae and other matter sink to the bottom and decompose, reducing oxygen levels.

We are seeing a transition from lake sediments, which act as sinks of contaminants due to the various environmental changes currently occurring, he notes.

In the case of Lake Charles, we find that recovery may also be influenced by contemporary environmental changes linked to urbanization and climate change.

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The traces left by gold extraction at Montague Gold Mines are clearly visible in this satellite image.

Mercury in Lake Gegogan and arsenic in Lake Charles exceed guidelines set by the Canadian Council of Ministers of the Environment , a federal benchmark for environmental contamination.

In Montague and Goldenville, tailings fields are also used by all-terrain vehicles, which that has accelerated the erosion of tailings that are moved to downstream aquatic ecosystems, the study says.

The report calls for more monitoring to track the movement of mine tailings.

With information from Paul Withers ofCBC

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