Communities located near uranium deposits that rely on underground well water for drinking are at higher risk of chronically ingesting low doses of uranium, the effects of which are not well known
A diagram visualizing the presence of uranium in ground water
Obvious kidney damage is the main thing scientists would expect to see in somebody who’s ingested a large amount of uranium. But what would they expect in somebody who’s consistently ingesting small amounts of the heavy metal?
That, the international research community isn’t absolutely certain about.
This chronic, low-dose context that Chalk River Laboratories researchers are investigating reflects the reality of communities whose drinking water supply relies on underground wells containing significant levels of uranium — a reality that Indigenous communities are at higher risk of facing because of the systemic barriers preventing sufficient drinking water infrastructure, monitoring, and treatment processes on reserves.
As part of this project being carried out for the Canadian federal government, the multidisciplinary team of researchers are working with experts from the Health Canada Radiation Protection Bureau to better understand how ingesting different concentrations of uranium affects the body over time. Their results will provide data that will inform whether the Canadian drinking water guidelines for natural uranium may need to be redefined.
In Canada, the maximum acceptable concentration for total natural uranium in drinking water is 0.02 milligrams per litre (mg/L). And this specific value originates from a study published in 1998 that analyzed the kidney-specific health effects seen in rats that were exposed to uranium-contaminated drinking water for three months.
Years later, though, this study’s results would conflict with those from a study done by Canadian Nuclear Laboratories (CNL) and the French nuclear safety and radiation protection authority, the Autorité de sûreté nucléaire et de radioprotection (ASNR), in 2014.
This joint project exposed rats to drinking water that contained concentrations of natural uranium up to 25,000-30,000 times greater than the Canadian guideline value — between 500 mg/L to 600 mg/L — and the researchers observed no signs of kidney toxicity.
“The results from these studies differing not only suggests that Canada’s current guidelines could be extremely overprotective, but it also highlights how important it is to be able to reproduce data across multiple laboratories when it’s being used to set regulatory guidelines,” explains the project’s technical lead, CNL biologist and biochemist Laura Bannister.
Uranium drinking water guideline values also fluctuate greatly around the world, further pointing to the lack of a unified, global understanding of how exactly the kidneys are affected by chronically ingesting low doses of uranium.
A diagram visualizing the animal study
“Being exposed to high doses of uranium over a short period of time damages the kidneys — but it’s mainly the heavy metal’s chemical composition that creates that damage, as opposed to its radioactive nature,” says CNL radiobiology researcher Qi Qi.
When ingested, some of that uranium gets absorbed into the bloodstream through the gut. These uranium ions then travel to the kidneys for filtration, but these heavy metal ions have a tendency to bind to cellular components in these tissues. Essentially stuck there, that uranium can then accumulate and disrupt or completely block cellular processes because the body doesn’t know how to excrete it. This can then lead to compromised kidney function, he explains.
Leveraging an internationally-recognized oral toxicity testing method from the Organization for Economic Co-operation and Development (OECD), the current research project exposed cohorts of rats to drinking water containing different concentrations of uranium for three months to investigate how it affected their kidneys, as well as whether the exposure caused any other biological changes that indicated harm, called biomarkers.
The team completed the project’s required 90-day exposure period this spring, which specifically tested the cohorts for dose-responses to uranium concentrations of 0 mg/L, 500 mg/L, 1,000 mg/L, and 2,500 mg/L. This included a cohort that was exposed to the highest concentration and then analyzed at 28 days, as well as a cohort that was exposed to the highest concentration and then returned to normal drinking for a month afterwards to understand if observed toxic effects could be reversed.
Though further analysis and validation is underway, researchers have already observed that the rats’ biological responses were different depending on whether they were male or female, as well as which dose of uranium they were exposed to — especially at the two higher concentrations. They observed and tracked these differences while measuring the rats’ body weights, organ weights, and blood and urine biomarkers throughout the exposure period.
“This research and its future results will help clarify the risks of chronic uranium ingestion and inform regulatory values. The work also has broader significance for Indigenous health equity and supports larger international efforts to develop science-based drinking water standards and kidney toxicity pathways,” says Qi.
This research is funded by Atomic Energy of Canada Limited’s (AECL) Federal Nuclear Science & Technology (FNST) work plan program, which connects federal organizations, departments, and agencies to the nuclear science expertise and facilities we have at Chalk River Laboratories.
Under this program, our researchers carry out projects designed to support the Canadian government’s core responsibilities and priorities across the areas of health, safety and security, energy, and the environment.
