In search of cleaner coal, scientists lace lake with toxic element

In tiny doses, selenium is not just good for you, but essential. All animals require trace amounts of this somewhat obscure element in order for certain enzymes to function properly.

But when mining digs up the Earth’s crust, enough selenium is released into the environment to harm fish and other animals. 

Researchers at the Experimental Lakes Area in northwestern Ontario are trying to determine precisely how selenium affects these animals in freshwater lakes.

In order to do that, they’re actually adding selenium to isolated columns of water and watching what happens to the organisms within.

“We don’t have a lot of data on what selenium does when it’s added to a system, especially in Canadian boreal lakes,” said Stephanie Graves, a University of Saskatchewan toxicologist who is leading a summer-long selenium experiment at the ELA, a freshwater-science facility encompassing dozens of lakes east of Kenora.

“We don’t know when it’s going to be a concern in Canadian systems.”

Perch minnows swim in the shallows of Rawson Lake at the Experimental Lakes Area. (Trevor Brine/CBC)

While minuscule amounts of selenium are essential for animals, higher levels can be toxic to fish and egg-laying invertebrates.

In humans, very large doses can lead to gastrointestinal disorders, liver problems, nerve damage and, in rare cases, death.

Selenium typically winds up in the environment as a result of mining coal and some types of metals.

“For you and I, it’s not a concern. But as soon as it’s taken up by any organism that lays an egg — fish, amphibians, birds and reptiles — it binds to egg protein,” said Vince Palace, head research scientist at the ELA.

“You can get rates of deformities increasing at concentrations that are really only slightly higher than those that are required in the [organism’s] diet.”

Research could have mining policy implications

While selenium is known to be toxic at elevated levels, how it’s taken up by different organisms is not well understood. It was also believed it may not be as harmful in Canada as it is in warmer parts of the planet, Graves said.

“Previously it was thought maybe in colder systems, there wasn’t much accumulation of selenium in organisms,” she said.

So this summer, she’s added different concentrations of selenium to a series of enclosures called mesocosms, which are columns of water sealed off from a surrounding lake by an impermeable membrane.

Inside each enclosure live algae, animal plankton, bottom-dwelling invertebrates and fish. Graves samples the water and sediment within the column twice a week and also monitors how the organisms within the enclosure are taking up selenium.

Water-column enclosures known as mesocosms are used to conduct research into the environmental effects of selenium on Lake 239 in the Experimental Lakes Area. Each enclosure is separated from the surrounding lake by an impermeable membrane. Fish, invertebrates and plankton live inside. (Bartley Kives/CBC)

While it will be a year before the PhD student publishes her findings, the early indication is that it doesn’t take much selenium to hurt creatures in freshwater lakes.

“We’ve seen first of all, a lot of accumulation and second of all, enough to cause toxicity at concentrations of 10 micrograms per litre of selenium, which isn’t very high,” Graves said.

If the preliminary results hold, the research could have policy implications for the mining industry. 

Graves said environmental monitoring downstream of coal mines could switch over to looking at selenium levels in fish, instead of sampling the water.

The mining industry could also change the way it remediates old sites or discharges selenium in the first place, she speculated.

The Coal Association of Canada has been asked to comment. Coal is mined in B.C., Alberta, Saskatchewan and Nova Scotia.

In 2017, Ottawa announced plans to impose new limits on discharges from coal mines in 2019.

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