Bioaccumulation, food web transfer, and tissue distribution of polonium-210 and lead-210 in Canadian freshwater ecosystems.

Understanding the bioaccumulation and trophic transfer of naturally occurring radionuclides is essential for assessing ecological risk in freshwater systems. This study provides a large-scale assessment of polonium-210 (210Po) and lead-210 (210Pb) bioaccumulation, trophic transfer and tissue-specific biodistribution in freshwater food webs across Canada. Activity concentrations were measured in water and biota samples collected from multiple ecozones and land-use settings. Bioaccumulation factors were calculated to evaluate water-to-food web transfer, while trophic position patterns and 210Po:210Pb activity concentration ratios were used to assess trophic transfer and preferential radionuclide uptake and retention. Results showed the bioaccumulation of 210Po in freshwater biota relative to surface water, while 210Pb was generally less enriched in biota and showed lower relative retention across organisms. Relationships with trophic position indicated that 210Po transfer was not well described by a linear trophic magnification factor, showing enrichment from primary producers to primary consumers, followed by substantial variability among higher trophic positions. The 210Po:210Pb activity concentration ratio was generally elevated in consumer organisms, indicating preferential biological uptake and retention of 210Po relative to 210Pb. Tissue-specific analyses indicated that 210Po was concentrated primarily in viscera and internal organs, whereas muscle contributed a smaller proportion of whole-fish 210Po burden. Together, these findings demonstrate that 210Po bioaccumulates, but its biological uptake and retention vary nonlinearly with trophic position, and that 210Po:210Pb activity concentration ratios provide a consistent and integrative metric of trophic enrichment.