Amphipods (Hyalella azteca) and zooplankton as sentinels of rare earth elements, uranium and thorium in a northern mining region contaminated with arsenic

Growing demand for green energy and new technologies is driving rare earth elements (REEs) mining, with implications on the bioavailability and accumulation of REEs and co-occurring radionuclides (U, Th) in aquatic organisms. We evaluated the amphipod Hyalella azteca and zooplankton as potential biomonitors for REEs, U, Th, and arsenic by sampling ten lakes in the historically arsenic-contaminated region of Yellowknife (NWT), near the Nechalacho REE mine. Lanthanum (La) concentrations were among the lowest reported in Canadian fresh waters (0.01-0.07 nmol L⁻¹). In zooplankton, La bioaccumulation was negatively influenced by protein-like dissolved organic matter and phosphate, U free ion concentrations best predicted U accumulation, and dissolved organic carbon was found to reduce Th accumulation. In H. azteca, littoral sediment La, U, and Th concentrations strongly predicted bioaccumulation, and aqueous carbonate complexation likely reduced U accumulation. Arsenate (As(V)) in surface water was an important predictor of La, U, and Th amphipod bioaccumulation. Even after EDTA washing, Fe strongly predicted La accumulation, suggesting an association beyond their surface adsorption. Key processes controlling the bioaccumulation pathways of La, U, Th, and As in this arsenic-contaminated region were summarized in a conceptual model, providing a risk assessment framework for REE mining in northern Canada.