Biodilution of technology-critical elements, including rare earth elements, in boreal lake food webs along a mining...

Mining and e-waste recycling release trace elements (TEs) that can accumulate in aquatic organisms and impair their vital functions. Predicting whether an element will biomagnify or biodilute in food webs is challenging, as it depends on the element, species, and environment. This is especially true for technology-critical elements (TCEs), including most rare earth elements (REEs), which remain largely unstudied and are currently unregulated in most countries, despite growing emissions into the environmental. To address the gaps in understanding pollution fate and ecological implications of these elements, we quantified concentrations of understudied TCEs (Ti, Sr, Co, Tl, REEs (La, Ce)), alongside conventional TEs (Cu, Zn, As, Se, Cd, Pb), in six organism groups spanning multiple trophic levels (Ephemeroptera, Diptera-Chironomidae, Amphipoda, zooplankton, Yellow perch, and Walleye) from six boreal lakes at varying distances from mining and e-waste recycling activities. We then examined biomagnification and biodilution patterns of these elements across food webs using stable isotope δ¹⁵N to determine trophic position (TP). TCEs, including Ti, Co, La, and Ce, consistently biodiluted across all lakes, similarly to the better-known TEs (Cu, Zn, As, Cd, Pb). Selenium was the only element to show significant biomagnification, and this pattern was observed exclusively in two remote lakes. Tl also showed a variable pattern, characterized by significant biodilution in some lakes and non-significant trophic relationships in others. The variability for Se and Tl suggests their trophic transfer depends on lake-specific ecological factors rather than exposure alone. Zooplankton consistently showed the highest concentrations within the food web for multiple elements (e.g., Ti, Co, Tl, La, Ce, Cu and Zn), making them a key contaminant entry point. This study provides needed evidence on TCE trophic dynamics in boreal lakes. These results inform pollution monitoring and ecosystem protection for freshwater environments across boreal regions impacted by mining and e-waste recycling worldwide.