Cumulative Anthropogenic Impacts of Past and Future Emissions and Releases on the Global Mercury Cycle

Humans have intentionally mined and released mercury (Hg) from the Earth's lithosphere over millennia. Here, we synthesize past, present, and future anthropogenic Hg emissions and releases and use a global geochemical box model to characterize accumulation in the atmosphere, land, and ocean. We project an upper-bound for emissions and releases between 2010 and 2300 (Shared Socioeconomic Pathway (SSP)5-8.5; 1.7 Tg) that surpasses the historical total over the past half millennium (1.5 Tg). In contrast, the lower-bound for emissions and releases (SSP1-2.6; 0.7 Tg) is substantially smaller than the historical total. Observational constraints on global modeling suggest that most Hg released to land and water prior to 2010 remains sequestered at contaminated sites. Substantial oceanic enrichment by anthropogenic Hg (270% ca. 2010) has been driven mainly by atmospheric emissions. Cumulative future releases to land and water are projected to be approximately six-times greater than primary anthropogenic emissions to the atmosphere. This Hg is mainly sequestered in legacy Hg waste pools and is unlikely to impact Hg pollution in the global ocean unless it is mobilized by climate change. Modeling results suggest that by 2100 atmospheric Hg concentrations may be similar to present levels if society follows SSP5-8.5. Declines in the surface ocean (-19%) and atmosphere (-45%) are expected under SSP1-2.6, emphasizing the benefits of reductions in future Hg releases.