Tungsten (W) is recognized as an emerging pollutant due to its detrimental impacts on both human health and the functioning of aquatic ecosystems. Traditionally, W was regarded as an insoluble metal with minimal ecotoxicological consequences. However, recent scientific studies have challenged this notion, and have revealed the toxicological and environmental effects associated with W exposure. This shift in perspective has led to tungsten’s recognition as a priority substance by esteemed regulatory bodies, including the U.S. National Toxicology Program in 2002, its designation as an emerging contaminant by the U.S. EPA in 2008, and its listing as a priority chemical for biomonitoring by the state of California in 2014. Evidence shows that concentrations of W in the urine of Washington State residents consistently surpass the national average. Elevated W levels in urine have been linked to an increased risk of various health issues, including stroke, diabetes, peripheral arterial disease, and altered thyroid function. Despite these concerning findings, understanding of W fate and effects in aquatic systems remains limited, highlighting a significant knowledge gap with substantial implications for water quality and ecosystems. The proposed research aims to address this critical knowledge gap by testing fundamental hypotheses regarding tungsten’s effects on nitrogen and carbon cycles, while also collecting comprehensive data on tungsten’s fate in aquatic environments. Specifically, long-term experiments will be conducted using mesocosms (aquaria) to assess the impact of tungsten on the inhibition of nitrate reduction and methanogenesis in anaerobic sediments. This research endeavor is expected to provide essential insights into the rates and controls governing tungsten mobility, distribution, and ecological effects, thereby advancing our fundamental understanding of hydrogeochemistry. Moreover, the findings will offer policy-relevant information crucial for regulatory agencies and policymakers. Additionally, the pilot data generated from this study will support compelling follow-up proposals aimed at securing more substantial funding from state and federal agencies.