Student aims for better assessment of uranium toxicity in sediment

Sarah Crawford
Sarah Crawford tests contaminated sediment and organisms at the U of S Toxicology Centre (photo: Jacob Ouellet)

By Lisa Buchanan

University of Saskatchewan researchers are trying to improve the way regulators and mine operators assess the risk of metal contamination from effluent discharged in uranium mining.

As Saskatchewan has one of the world's largest high-grade uranium deposits, metal accumulation in lakes and streams downstream of effluent discharge points is of concern to both government and the mining industry.

Metal accumulation affects not just the water, but also the sediment below. The key when assessing contamination risk is whether the metals are biologically available to be absorbed and used by organisms, says U of S toxicology PhD student Sarah Crawford.

"We know that metals, such as uranium, can accumulate in sediment as a result of mining activity, but there is limited information regarding the bioavailability and toxicity of uranium to organisms exposed to uranium-contaminated sediment," she said.

While there may not be direct toxic effects on humans, uranium contamination can adversely affect small organisms that make their home in sediment and serve as a food source for many fish and birds, she said.

With funding from the federal Natural Sciences and Engineering Research Council, she is studying how sediment components influence the bioavailability, and thus toxicity, of uranium.

While federal guidelines are in place to assess the risk metals in sediment pose to aquatic organisms, researchers say these guidelines need to be improved to evaluate true risk. Current guidelines use total concentration of metals in sediment to predict impact on aquatic ecosystems. This approach has been criticized because there is not always a cause and effect relationship between total concentrations and toxicity and it rarely pinpoints which metals are responsible for contamination at a particular site.

Crawford hopes her research will contribute to the development of more science-based and region-specific regulations and improve management of uranium concentrations downstream of mining operations in northern Saskatchewan.

"From a financial perspective, government and industry want to put their resources for site management and reclamation toward the most important problems or the greatest risks," said Crawford's supervisor, Toxicology Centre director Karsten Liber.

One reason for the lack of advancement in designing effective guidelines is that regulations must be easy to implement. Crawford's approach combines measurements already being taken in the field, making it easy for researchers and regulators to implement.

Her model combines the total concentration of metals in the sediment with information such as the amount of clay and organic matter present and the sediment pH to estimate the bioavailability of uranium. Because metals often have a high capacity for binding with clays and organic matter, these common sediment components can reduce the bioavailability of many metals.

Other measurement combinations have been used elsewhere for other metals, but Crawford's approach is unique in Canada. While she focuses on uranium, her approach could be applied to other metals.

Lisa Buchanan is a graduate student intern in the U of S Office of Research Communications.

This article first ran as part of the 2012 Young Innovators series, an initiative of the U of S Research Communications office in partnership with the Saskatoon StarPhoenix.