Permafrost underlies 22% of the Northern Hemisphere's exposed land surface and is thawing at an alarming rate as a direct consequence of global warming, releasing large quantities of organic matter and contaminants into the environment. These contaminants, which includes heavy metals, persistent organic pollutants and microbiological agents, pose a serious risk for both wildlife and human health. Many studies have estimated stocks of contaminants, particularly heavy metals, and attempted to assess the impact of their potential release on Arctic ecosystems and Indigenous populations. However, a broader and holistic approach to permafrost thaw was only recently proposed by the EU Project ILLUQ within a One Health framework and involved the release of contaminants and their impacts on Arctic flora and fauna, infrastructures, sanitation and human health. However, several environmental and biological factors (biogeochemical processes) could catalyze changes in speciation, partitioning, transport and fate of released contaminants. Such alteration could potentially alter the toxicity after their initial release and must also be considered in risk assessments. The ILLUQ-PT proposal adds this process component to ILLUQ aiming to investigate those post-release processes. Using arsenic and mercury as target contaminants, we will investigate how the speciation of these elements may change in permafrost thaw ecosystems and how these changes are controlled by key biogeochemical factors (e.g., organic matter content and quality, microbiome diversity and taxonomic composition or the role of vegetation). We propose to utilize stable isotope techniques (e.g., isotope fractionation) to investigate their potential to track contaminant pathways and to measure the rates of those changes. Finally, ILLUQ-PT aims to better link the release of trace-elements from thawing permafrost with the risk of exposure to Arctic wildlife and Indigenous Populations.