The NWT's chief public health officer has provided an update about arsenic levels in the soil and water around Yellowknife.
Using new data, the territory has amended a map of the city showing two important pieces of information:
- an "area of interest" in which residents are advised not to harvest foods like berries and mushrooms, since high levels of arsenic have been found in the soil; and
- levels of arsenic in the city's lakes.
Friday's update in part uses information drawn from a recent study conducted by the Giant Mine clean-up project.
The update does not mean the threat from arsenic has been upgraded; it simply adds more information to a pre-existing map based on new data.
For example, Niven Lake, Range Lake, and Fiddler Lake receive arsenic indicators for the first time – showing all three lakes contain between 10 and 51.9 parts per billion of dissolved arsenic. This is above Health Canada's maximum drinking water guideline of 10 parts per billion, but is not considered especially dangerous and is significantly lower than the value for more contaminated lakes nearer the Giant mine site.
Giant Mine was the source for much of Yellowknife's arsenic contamination, thanks to mining and gold roasting processes used at the site while it was operational last century. The federal government is starting a billion-dollar project to remediate the mine site itself, but the broader area around Yellowknife contains significant low-level contamination.
"This is a precautionary advisory. It’s really to make sure that nobody accidentally, or unknowingly, would expose themselves to high concentrations of arsenic," said Dr André Corriveau, the chief public health officer for the Northwest Territories.
"Most of the lakes that are used recreationally on a regular basis are actually safe to do so. We’re not saying you can’t fish in a lake with a higher concentration, but you shouldn’t eat the fish as a regular meal.
"Until now, we didn’t have data on two lakes that are smack in the middle of Yellowknife. In Niven Lake, which I think most people wouldn’t think of using recreationally, it turns out the arsenic level is quite low. And then Range Lake, which is also around a residential area, we didn’t have data on it and now it’s on the map."
Though arsenic levels are not disproportionately high for Niven Lake, officials also discourage swimming or berry picking in the vicinity as the lake was formerly a sewage lagoon.
'The best we can provide'
New soil contamination data has led the territory to adjust its "area of interest," in which Dr Corriveau says residents should avoid harvesting wild plants, mushrooms, and small fruits.
"A little bit north of Long Lake and then going up towards the mine they have done a few soil samples that were elevated," said Dr Corriveau, clarifying the change made to that area on the map, "so we’ve included them."
He continued: "It doesn’t automatically mean picking berries there would be problematic but, until we have data, we can’t say for sure. At this point, this is the best information we can provide."
Arsenic cannot be absorbed through the skin – it must be ingested – so the advisory applies only to activities in which someone may end up consuming lake water, fish, or fruits, plants, and fungi from areas show on the map.
Dr Corriveau said people with their own gardens or raised beds using imported soil, not native soil, were not believed to be at any risk.
"We have some data on that from a few years back and I think more will be done in the coming years, where people can bring produce for testing. At this point, unless you’re using only native soil, your garden should be fine."
The map will be continually updated as new data regarding soil and lake contamination around Yellowknife becomes available.
Friday's update does not alter the territory's longstanding advice regarding arsenic in and around Yellowknife.
Drinking water supplied by the City is well within federal arsenic guidelines and not considered a concern. Drinking water from lakes near historic industrial sites, like the Giant and Con mines, is riskier – boiling it will not remove the arsenic – and shouldn't be done, but most lakes are safe for recreational use like swimming.
Lakes shown with an orange, red, or purple dot on the map (link above) shouldn't be used as regular recreational spots, and don't eat fish from those lakes.
Frame Lake is said by officials to be fine for paddling and the nearby trail and parklands, but don't swim in it or eat any nearby berries or plants. The same advice applies to Kam Lake. There are no issues with any activities at Grace Lake or Range Lake.
Unless you're a mushroom expert, err on the side of caution and don't eat local mushrooms. But check the Q&A linked above for more detailed information.