Mercury budget in global rivers at present-day: impacts from reservoirs and dams

Many world rivers are currently polluted by mercury (Hg) compounds, leading to the bioaccumulation of methylmercury (MeHg) in the food web, which poses potential health risks to humans. However, the riverine Hg budgets of global scale remain poorly understood due to limited observations, complicating efficient environmental governance. Here, we employ a process-driven Hg model to track its journey from sources to the global ocean and assess its human exposure. Our findings indicate that ~1,500 Mg/yr of human-induced Hg are released plus ~400 Mg/yr (mean) of soil erosional Hg are released to rivers. Due to the trapping effects of reservoirs/dams, about 50% of the riverine Hg (~1,000 Mg/yr, mean) reaches the ocean. The different strengths of the human-induced Hg releases and/or the numbers of (mega-) reservoirs/dams in regions would greatly impacts the riverine Hg budgets of the corresponding regions. Human-induced Hg releases have led to an accumulation rate of approximately ~1,000 Mg/yr in global reservoirs at present-day levels. This has resulted in large Hg pools in reservoirs and dams, posing significant risks to future Hg pollutant restoration efforts. Our model enhances the understanding of the fate of riverine Hg, providing critical information for riverine Hg management and human health mitigation strategies.