A study of produce grown in gardens around Yellowknife, Ndilǫ and Dettah shows that local veggies have slightly higher levels of arsenic than what you’d buy from the grocery store — but the risk of getting cancer from them is still considered to be very low.
And, in a finding that surprised Michael Palmer, manager of the North Slave Research Centre at Aurora College and Iris Koch, an adjunct associate professor at Royal Military College (RMC) in Kingston, locally grown produce also revealed higher levels of nutrients.
The findings are based on samples gathered from 47 garden plots in the area in 2020, as part of a two-year study, which also collected another 40 samples this year, that aims to answer a question Palmer said he hears often.
That is, whether or not it’s safe to eat vegetables grown in the three communities.
“The lived memory of mining in the region is still pretty strong,” said Palmer. “There was a huge amount of people that were interested in this project … it shows us that people are still really interested in knowing about this, and it’s a persistent concern in peoples’ minds.”
During more than half a century of mining, 19,000 tonnes of toxic arsenic trioxide dust went up the stacks of smelters at the Giant and Con gold metal mines and settled on land and lakes in and around the city.
Palmer said it’s important to understand the range of arsenic levels in garden soils because people use soil from a variety of sources — including local quarries and bagged from hardware stores — and because of a rise in agricultural initiatives in the area.
The results related to arsenic are similar, said Palmer, to the results of a smaller study carried out by RMC’s Environmental Sciences Group in 2001. In that study, researchers looked at 11 gardens and found that Yellowknife garden produce was safe to eat despite having levels of arsenic that were higher than the Canadian average.
Risk assessment based on lifetime of blended diet
Palmer said he and other researchers decided to do a “much larger” survey than the one two decades ago, which would also incorporate a risk assessment that Koch called a “critical tool” for putting the figures into context.
Because of the pandemic, Palmer said they took a “citizen’s science” approach and asked residents to submit soil and vegetable samples — including carrots, potatoes and leafy greens — from their gardens last year.
Those samples were sent to labs at RMC and Queen’s University in Ontario, and were analyzed for metals including arsenic, antimony and lead. The results being presented this year, said Palmer, focus on arsenic levels “because that seems to be people’s concerns.”
In order to better understand the risk of cancer from arsenic in locally grown vegetables, Koch said a risk assessment scenario was developed. It compared a diet of produce that came entirely from a grocery store and a diet in which 90 per cent of the produce came from the grocery store and 10 per cent came from a Yellowknife garden over an 80-year lifetime.
The result was that eating the blended diet carried a “very low risk” of causing cancer.
The risk assessment, said Koch, is based on Health Canada’s guidelines for calculating cancer risks, which considers the added lifetime cancer risk to be negligible if it’s less than 1 in 100,000. The study defined “very low risk” as being between 1 and 10 in 100,000, and low risk between 10 and 100 in 100,000.
The “very low risk” associated with eating a blended diet for an 80-year lifetime is comparable, said Palmer, to taking a return three-hour flight once a year for 60 years. “There’s a risk associated with that, from increased radiation,” he explained.
Higher concentration of nutrients
Researchers also discovered that levels of calcium, iron, potassium and zinc were often much higher in locally grown vegetables than in grocery store vegetables.
For example, locally grown chard contained potassium in a concentration of 5,700 parts per million (ppm) compared to the 3,800 ppm researchers obtained from the Canadian Nutrient File (CNF), a standard reference food composition database maintained by the federal government.
Potassium in locally grown kale was found at a concentration that was 1,770 ppm higher than in the CNF, in local lettuce it was 1,700 ppm higher and in local potatoes it was 3,680 higher. In carrots, the concentration of potassium was the same, and in spinach, it was down 650 ppm.
Calcium in local carrots was found at a concentration that was 220 more ppm, in chard the concentration was 590 ppm higher, in kale it was 1,540 ppm higher, in lettuce it was 1,150 ppm higher and in spinach it was 1,300 ppm higher. In potatoes, calcium was found at a concentration that was 20 ppm less than in the CNF.
All locally grown vegetables had higher levels of iron and zinc as well.
Koch was hesitant to suggest that nutrients could offset the risks of arsenic. Palmer re-iterated that none of the study’s findings suggested people should be discouraged from eating locally grown vegetables.
“Nutrient levels are substantially higher in your home gardens of Yellowknife gardens, so that’s an important source of nutrients for people.”
Impact of peeling, cooking to be examined
There’s still another year of the study left.
Researchers plan to examine whether peeling or cooking vegetables changes the level or risk associated with arsenic, how vegetables absorb metals at different stages throughout their growing cycles, and why levels of arsenic are higher in Yellowknife produce.
The study is a joint initiative between the Aurora Research Institute, RMC, Queen’s University and the Yellowknives Dene First Nation. It received funding from the N.W.T.’s environment and natural resource department.