Environmental occurrence and empirical assessment of polonium-210 in freshwater environments

Polonium-210 (²¹⁰Po) is an important naturally occurring radionuclide in freshwater environments, yet large-scale datasets describing its occurrence and geochemical associations remain limited. Here we present a multi-compartment dataset of ²¹⁰Po, and lead-210 (²¹⁰Pb) activity concentrations compiled from Canadian freshwater systems, addressing longstanding gaps arising from the predominance of site-specific or marine focused studies. Activity concentrations varied widely among compartments and sites, reflecting broad spatial variability in hydrological and geochemical conditions. Simple linear regressions showed that ²¹⁰Pb was strongly associated with ²¹⁰Po across several abiotic compartments, with moderate to high explanatory power in surface waters, suspended particles, and sediment. For surface waters, multiple linear regression identified dissolved organic carbon (DOC), dissolved uranium (U), and calcium (Ca²⁺) as the strongest measured explanatory variables associated with ²¹⁰Po activity concentrations. Complementary random-forest and generalized additive model analyses supported the recurring importance of these variables, although the models explained only a moderate proportion of total variability. These associations are interpreted as reflecting organic matter interactions, lithogenic source contributions, and cation-mediated particle processes. The resulting internally validated empirical models provide screening-level estimates of ²¹⁰Po occurrence within the range of Canadian freshwater conditions represented in this dataset. Furthermore, observed activity concentration ranges provide comparative context for future monitoring and site-specific assessments.