Health advisory coming for arsenic in tiny lakes
Report examines 25 very small bodies of water that points to continuing legacy of Giant Mine
Shane Magee
Northern News Services
Wednesday, April 13, 2016
SOMBA K'E/YELLOWKNIFE
The NWT's chief public health officer is planning a health advisory after a university study released last week showed arsenic levels above drinking water standards in several very small lakes near Giant Mine.
University of Ottawa PhD student Adam Houben measuring water quality in the Yellowknife area as part of a study released last week that found arsenic levels higher than federal drinking water guidelines in some of the small lakes near the city. - photo courtesy of Adam Houben |
"Many of them are just like ponds. That's the problem, they don't have very good drainage unlike the larger lakes where there's more flow-through and would have flushed (the arsenic) out," said Andre Corriveau said.
He said he plans to issue a health advisory to tell people to avoid using the lakes for fishing or as a source of drinking water. The goal is to issue the advisory before the snow and ice melts.
"We don't really think that it's an area that people would've used to fish or as drinking water unless you're camping there and using the water," he said.
The study published last week in the journal PLOS ONE by researchers at the University of Ottawa examined 25 small lakes in 2010 within 25 kilometres of the mine where ore was roasted to extract gold, sending an estimated 20,000 tonnes of toxic arsenic trioxide into the atmosphere.
The largest is 0.17 square kilometres in size - less than a quarter of the size of Frame Lake.
"We showed a very clear increasing concentration the closer you got to the mine," said Adam Houben, a PhD student at the university who was lead author of the study.
The latest study adds to a previously reported study of lakes in the region that found elevated concentrations of arsenic in 45 per cent of 98 lakes sampled within 30 kilometres of the city. The lakes sampled represent only two per cent of the more than 4,000 lakes in the 30-kilometre radius.
Some lakes near the new highway bypass around the mine were more than 10 times higher than the 10 micrograms per litre limit for drinking water. One was 60 times over the limit.
That report, by the Northwest Territories Geological Survey, noted the size of the lakes was an important factor in the concentration of arsenic. The amount found in lakes larger than two square kilometres was typically within acceptable levels, even those closer to the mine site.
The latest report sampled small, shallow lakes that are not believed to be used as sources of drinking water.
"We're speculating that there's more flow through on those larger lakes, so those contaminants are getting flushed away," Houben said.
The drinking water guidelines are based on someone consuming the water daily for many years, so Corriveau said it's unlikely there's been much exposure.
"We don't think it's a likely scenario but we can't say it hasn't happened," he said.
Further study is needed into the concentrations of arsenic in things like berries, fish and humans, he said.
The latest study started as research into melting permafrost in the North but researchers focused in on arsenic concentrations after test results of the water were obtained.
The lakes were selected based on whether there was nearby road access so they could be reached by foot, although still removed from sources of pollution such as roads crossing water catchments. The samples were collected in the summer of 2010.
Houben said there's already a good amount of research on the toxic legacy left behind at the mine site but the study he worked on and the GNWT's study examined the broader impact.
Ore mined at Giant was heated to extract the gold but that process released tonnes of arsenic trioxide laden dust into the atmosphere.
For three years, there was no mechanism in place to try and capture the byproduct before it was released.
In 1951, the mine added emission control technology and arsenic emissions gradually reduced over time. The mine still has about 237,000 tonnes of arsenic now stored underground.
An estimated 20,000 tonnes of arsenic trioxide was released to the surrounding area between 1948 and 1999, according to a GNWT report.
Con Mine had far less roasting and much of it was captured and integrated with tailings or shipped south.
One thing the smaller study uncovered that hadn't been examined before was elevated levels of highly toxic methyl mercury in lakes closer to Giant. One of the risks posed is that mercury is known to concentrate in fish.
The study did not examine the Yellowknife River, which is the source of the city's drinking water supply, which is regularly checked for arsenic levels.
The authors note the chances for contamination of the river water is lower than the lakes because it has a greater catchment area - around 10,000 square kilometres - than the small lakes sampled and a higher flow.
