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December 15, 2021

CNL Advancing Research & Measurement of Polonium-210

Canada is one of the world’s largest uranium producers and will play a significant role in meeting future world demand for uranium-based fuels. Case in point, most of the small modular reactor (SMRs) designs considered for deployment in Canada alone require uranium-based fuels. The extraction of minerals or materials from the earth is a heavily regulated activity, ensuring that the necessary protections are in place to protect the environment. Guiding this regulation is a sound understanding of the potential risks, including possible contaminants, that could appear before, during or post operation.  This is where CNL’s Isotopes, Radiobiology and Environment Directorate fits in. In a project funded by AECL’s Nuclear Science and Technology (FNST) Work Plan, CNL has been leading research focused on the environmental behaviour of the most common polonium isotope, polonium-210 (Po-210).

Why Po-210? Although it exists all around us, in very low levels in the environment and in our bodies through the food chain, Po-210 also occurs in uranium ore and tailings. Reviewing the literature, the team noticed elevated Po-210 concentrations in freshwater in decommissioned and active mining areas in the Northwest Territories, Ontario and Saskatchewan.  While there have been studies focused on marine ecosystems, there is less data about it in freshwater ecosystems due to the difficulty in measuring Po-210. CNL’s Environment and Waste Technologies Branch recent projects are shedding light on the processes and factors influencing naturally-occurring levels of Po-210 in freshwater, information which could help inform regulation and build an understanding of the potential impacts as a result of mining operations.

“In the first project, we found some of the highest values for naturally-occurring Po-210  in freshwater streams rich in humic acids (‘tea-coloured waters’) in western Ontario”, says David Rowan, Radioecologist. “Higher levels of Po-210 in streams draining three wetlands and slightly elevated levels of it where streams enter Lac Granet in western Québec, informed a second study – a look at the biological, geological, chemical and foodweb processes controlling the fate and transport of Po-210 in aquatic ecosystems”, adds Matt Bond, Environmental Biologist.

In the second project, the team wanted to understand how Po-210 moves through a watershed and ends up in lakes, rivers and streams. And once it does end up in those rivers and streams, how it affects aquatic life. They found that Po-210 concentrations appear to be naturally elevated in acidified environments, especially those with relatively large wetland areas, and water pH and organic carbon appear to play an important role in Po-210 fate and transport.

As for the challenge of collecting and preparing Po-210 field samples for analysis, polonium can be lost by volatilization at low temperatures as well as through radioactive decay due to its relatively short half-life (140 days). These limitations mean analysis must be completed within 30 days of sample collection.

“Working with CNL’s Analytical Chemistry Branch, we were able to develop a method to measure naturally-occurring levels of Po-210 in freshwater samples that we couldn’t measure in the past,” says Stephanie Walsh, Research and Development Officer. “We were also able to modify this method for saltwater, sediment and biota such as invertebrates, algae, vegetation and fish.”

What impact will these findings have? Simply put, understanding what influences Po-210 levels in freshwater environments will help predict environmental impact and risk with uranium mining development. They also help determine geographic locations that might be naturally-enriched in Po-210, and provide the sound scientific understanding that informs everything from environmental protections to the steps needed to support the health of workers on mining sites and the residents in surrounding communities.

The team’s work and their research continues – now taking them to northern Saskatchewan over the next two years to better understand fate and transport of Po-210 in the province’s uranium mining regions, alongside collaborators from a Canadian university and First Nation communities.

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