Chronic radium-226 bioaccumulation and toxicity in the aquatic invertebrate Daphnia magna

This version of the article has been accepted for publication, after peer review (when applicable) and is subject to Springer Nature’s AM terms of use, but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at: https://doi.org/10.1007/s00244-024-01109-2

Natural Sciences and Engineering Research Council of Canada (NSERC) Alliance Grant (reference number ALLRP 566677-21). This work also received financial support from NexGen Energy Ltd., Orano Canada Inc., Canadian Nuclear Laboratories Limited, CAMECO Corp., Denison Mines Corp., BHP Billiton Canada Inc., and the Government of Saskatchewan.

Peer Reviewed

Mining operations in Canada, including uranium mining and milling, generate by-products containing radionuclides, including radium-226 (226Ra), a long-lived, bioaccumulative calcium (Ca2+) analog. Despite strict discharge regulations, there is limited evidence to suggest that current thresholds for 226Ra adequately protect aquatic organisms. Furthermore, Canada lacks a federal water quality guideline for 226Ra, underscoring the need for protective limits to safeguard aquatic ecosystems. Hence, this research aimed to generate data on 226Ra toxicity to the model aquatic invertebrate Daphnia magna. For this purpose, two 21-day chronic toxicity tests with D. magna were conducted, with survival and reproduction as the endpoints, as well as a reduced water hardness experiment, a multigenerational study, and a bioaccumulation assay. These experiments demonstrated that a high activity concentration (nominal 50 Bq/L) of 226Ra can significantly impact the survival of D. magna. 226Ra was also found to bioaccumulate in D. magna with a BAF of 72.8. Since the Canadian Metal and Diamond Mining Effluent Regulations (MDMER) monthly mean effluent limit is currently set at 0.37 Bq 226Ra /L, the limit for composite samples at 0.74 Bq/L 226Ra, and the limit for grab samples at 1.11 Bq/L 226Ra, it is unlikely that toxic effects to aquatic cladocerans like D. magna from 226Ra will be observed downstream of Canadian mines and mills.