Polonium-210 in Freshwater Environments: Analytical Advances, Predictive Modelling, Food Web Transfer and Dose Assessment

Abstract

Polonium-210 (²¹⁰Po) is a naturally occurring radionuclide of high radiological relevance, yet its occurrence, environmental behaviour and biological transfer in freshwater ecosystems remain poorly characterized. Advances in understanding have been constrained by analytical challenges and by radiation protection frameworks that historically emphasized human health, with ecological risks only more recently being addressed. This thesis addresses these knowledge gaps by validating a rapid, highly sensitive method for measuring ²¹⁰Po, and its parent radionuclide lead-210 (²¹⁰Pb), in diverse environmental matrices and applying this method to conduct the most spatially extensive survey of ²¹⁰Po and ²¹⁰Pb in Canadian freshwater systems to date.

The optimized copper sulphide (CuS) micro-precipitation method achieved high chemical recoveries (>90%), low detection limits (~ 0.01 mBq·L⁻¹), and high sample throughput. Its sensitivity and efficiency enabled the development of a comprehensive database of ²¹⁰Po and ²¹⁰Pb activity concentrations across 31 freshwater systems, spanning abiotic compartments and food webs. Complementary non-radiological data were also collected, and integrated statistical and machine-leading analyses identified dissolved organic carbon, dissolved uranium and calcium as key predictors of ²¹⁰Po activity concentrations in surface waters, with predictive accuracies up to 76%. These results highlight the roles of local geology and water chemistry in driving radionuclide mobility and suggest that climate driven processes such as permafrost thaw and lake browning may further influence ²¹⁰Po behaviour in freshwaters. A strong radiological association between ²¹⁰Po and ²¹⁰Pb was also confirmed for the abiotic compartments.

Food web analyses revealed that water chemistry, particularly electrical conductivity and dissolved uranium, significantly influenced biological uptake. Trophic magnification factors demonstrated clear biomagnification of ²¹⁰Po and trophic diminution of ²¹⁰Pb, with ²¹⁰Po:²¹⁰Pb activity ratios increasing with trophic position, reflecting preferential assimilation of ²¹⁰Po. Site- and tissue-specific transfer parameters (bioaccumulation factors, sediment-water partition coefficients) were derived, showing consistent patterns of ²¹⁰Po uptake across the broad spatial scale and support the use of a single set of empirical parameters for ²¹⁰Po uptake in Canadian radioecological risk assessments. Finally, dose assessments showed that benthic invertebrates experienced the highest internal exposures, while fish viscera disproportionately contributed to whole-body dose burdens.

Collectively, this work provides new tools, empirical data and predictive insights that advance understanding of ²¹⁰Po occurrence and transfer in freshwater environments. The findings establish a transferable framework for measuring and forecasting ²¹⁰Po mobility, refining radioecological risk assessments, and guiding environmental protection strategies under both natural conditions and in the context of climate and land-use change.