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 (²²⁶Ra). Even with the strict discharge regulations in place, there is limited evidence to suggest that the current Canadian regulatory thresholds for ²²⁶Ra are protective for aquatic life. This concern underscores the importance of generating toxicity data for ²²⁶Ra, as no federal Canadian water quality guidelines for ²²⁶Ra currently exist to safeguard aquatic ecosystems. The potential ecological risks of ²²⁶Ra 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 (Ca²⁺). Considering this, the primary objective of this research was to gather data on the toxicity of ²²⁶Ra 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 ²²⁶Ra (25.5 Bq/L) can significantly impact the growth of C. dilutus. However, none of the other nonlethal endpoints were significantly affected by ²²⁶Ra exposure, and there was no evidence of oxidative stress in exposed C. dilutus. Finally, ²²⁶Ra was shown to adsorb onto the silica sand used as a substrate for all experiments and desorbed following acid extraction.