Chronic Radium-226 toxicity to and oxidative stress in the aquatic invertebrate Chironomus dilutus.

The mining industry, including uranium mining and milling, is of high importance in Canada. It is, however, important to consider that ore processing can result in the creation of by-products that contain radionuclides such as radium-226 ((226)Ra). Even with the strict discharge regulations in place, there is limited evidence to suggest that the current Canadian regulatory thresholds for (226)Ra are protective for aquatic life. This concern underscores the importance of generating toxicity data for (226)Ra, as no federal Canadian water quality guidelines for (226)Ra currently exist to safeguard aquatic ecosystems. The potential ecological risks of (226)Ra are significant due to its high mobility under typical environmental conditions, long half-life (t(1/2) ~ 1,600 years), bioaccumulative properties, and similarity to calcium (Ca(2+)). Considering this, the primary objective of this research was to gather data on the toxicity of (226)Ra to the aquatic invertebrate Chironomus dilutus. For this purpose, a partial life cycle experiment was conducted, with larval growth, survival and pupation, and emergence and sex ratio of emerged adults, as the experimental endpoints. In addition, an assessment of oxidative stress as a potential cause of toxicity was performed. These experiments revealed that elevated activity concentrations of (226)Ra (25.5 Bq/L) can significantly impact the growth of C. dilutus. However, none of the other nonlethal endpoints were significantly affected by (226)Ra exposure, and there was no evidence of oxidative stress in exposed C. dilutus. Finally, (226)Ra was shown to adsorb onto the silica sand used as a substrate for all experiments and desorbed following acid extraction.