Radium-226 bioaccumulation and toxicity in the great pond snail Lymnaea stagnalis

Radium-226 (²²⁶Ra) may be of concern to aquatic ecosystems, because of its long half-life (1600 years), its potential for bioaccumulation and its radiotoxicity. Yet, in Canada, there is currently no ²²⁶Ra water quality guideline for the protection of aquatic life. To better evaluate the ecological risk of this radioelement in Canadian fresh waters, we conducted toxicity tests with the great pond snail Lymnaea stagnalis. Because of the analogy between ²²⁶Ra and calcium, this calciphilic organism was expected to readily bioaccumulate ²²⁶Ra, particularly during its early-life stage. We performed two chronic toxicity tests with aqueous ²²⁶Ra activity concentration ranging from 0.1 and up to 100 Bq/L: i) a 28-day juvenile test with newly-hatched snails (measurements: growth and survival) and ii) a 52-day early-life stage (ELS) test encompassing the embryonic stage (measurements: growth, hatching success and survival) and the juvenile stage (measurements: growth, survival and oxidative stress). In the ELS test, ²²⁶Ra bioaccumulated four times more in the shell than in the whole-body soft tissues. Overall, there was almost no apical effect of ²²⁶Ra on L. stagnalis in the tested concentration range, with only a slight evidence of juvenile survival reduction at [²²⁶Ra] ≥ 50 Bq/L in the ELS test (NOEC = 4.27 Bq/L, LOEC = 26.7 Bq/L, MATC = 10.7 Bq/L). In 52-d exposed snails, there was a slightly significant positive effect of ²²⁶Ra on glutathione peroxydase (GPx) activity. Our study suggests that [²²⁶Ra] in contaminated and uncontaminated fresh waters (0.0002 - 7.8 Bq/L) is unlikely to have toxic effects on L. stagnalis.