New research could reshape Canada’s drinking water guidelines for uranium

A team of scientists at Chalk River Laboratories, working with Health Canada’s Radiation Protection Bureau, is investigating how chronic exposure to uranium at different concentrations affects the body.

Their findings could help determine whether Canada’s drinking water guidelines for uranium should be updated. Currently, the maximum acceptable concentration of natural uranium in Canadian drinking water is 0.02 milligrams per litre, a limit set more than two decades ago based on a 1998 rat study.

However, research conducted in 2014 by Canadian Nuclear Laboratories (CNL) and France’s Autorité de sûreté nucléaire et de radioprotection raised new questions. In that study, rats were given drinking water containing uranium concentrations 25,000 to 30,000 times higher than the Canadian guideline, yet no signs of kidney toxicity were observed. 

“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,” said Laura Bannister, project technical lead and CNL biologist and biochemist.

Communities that rely on underground well water near uranium deposits face a heightened risk of chronically ingesting low doses of uranium, but scientists still lack clear answers about the long-term health impacts, the research team says. While it is well established that large doses of uranium can cause kidney damage, researchers are less certain about what happens when people are exposed to smaller amounts over time. Indigenous communities are particularly vulnerable, given the systemic barriers that limit adequate drinking water infrastructure, monitoring, and treatment on reserves.

International inconsistencies further complicate the issue, with uranium drinking water guidelines varying widely between countries.

“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,” explained Qi Qi, a CNL radiobiology researcher, in a statement to media.

When ingested, uranium enters the bloodstream through the gut and travels to the kidneys for filtration, but the heavy metal ions tend to bind to kidney tissue. Trapped there, uranium can interfere with or block essential cellular processes, eventually impairing kidney function.

To better understand these processes, the current Chalk River project followed an internationally recognized toxicity testing protocol from the Organization for Economic Co-operation and Development. Over a 90-day period, rats were exposed to water containing uranium concentrations of 0, 500, 1,000, and 2,500 milligrams per litre. Additional cohorts were studied at shorter intervals or allowed to return to normal drinking water to determine if toxic effects could be reversed.

Preliminary findings suggest that biological responses varied depending on the sex of the rats and the level of exposure, with more pronounced differences at higher concentrations. Throughout the study, researchers tracked body weights, organ weights, and biomarkers in blood and urine. Though analysis is still underway, the team has already seen measurable differences in how male and female rats responded to uranium exposure.

“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,” noted Qi.