Mercury as a Global Pollutant: Sources, Pathways, and Effects

TLDR

Mercury is a global pollutant whose anthropogenic emissions exceed natural sources, leading to accumulation in soil and deep ocean reservoirs and long‑term atmospheric transport, with methylmercury production in reducing environments linking inorganic inputs to human and wildlife exposure. The authors synthesize knowledge of mercury sources, atmospheric‑land‑ocean dynamics, health effects, and policy implications, and argue for integrating Hg science into national and international policy to target and assess control efforts. Human exposure to methylmercury is mainly driven by consumption of estuarine and marine fish, with methylmercury formed in reducing zones of freshwater, terrestrial, and coastal ecosystems. The most vulnerable group is developing fetuses, while highly exposed populations and wildlife also face significant neurotoxic risks.

Abstract

Mercury (Hg) is a global pollutant that affects human and ecosystem health. We synthesize understanding of sources, atmosphere-land-ocean Hg dynamics and health effects, and consider the implications of Hg-control policies. Primary anthropogenic Hg emissions greatly exceed natural geogenic sources, resulting in increases in Hg reservoirs and subsequent secondary Hg emissions that facilitate its global distribution. The ultimate fate of emitted Hg is primarily recalcitrant soil pools and deep ocean waters and sediments. Transfers of Hg emissions to largely unavailable reservoirs occur over the time scale of centuries, and are primarily mediated through atmospheric exchanges of wet/dry deposition and evasion from vegetation, soil organic matter and ocean surfaces. A key link between inorganic Hg inputs and exposure of humans and wildlife is the net production of methylmercury, which occurs mainly in reducing zones in freshwater, terrestrial, and coastal environments, and the subsurface ocean. Elevated human exposure to methylmercury primarily results from consumption of estuarine and marine fish. Developing fetuses are most at risk from this neurotoxin but health effects of highly exposed populations and wildlife are also a concern. Integration of Hg science with national and international policy efforts is needed to target efforts and evaluate efficacy.