Atmospheric mercury: Long-term (Late Pleistocene – Holocene) variations in mercury accumulation reconstructed using environmental archives

Abstract

Mercury (Hg) is a naturally occurring element that is found throughout the world. Due to the toxicity of its methylated forms (MeHg) to wildlife and human health, Hg is considered a metal of major environmental concern. According to numerous health and governmental organizations, billions of people are currently at risk of high exposure to poisoning by Hg due to a diet rich in fish (high content of MeHg) or by exposure to Hg emitted from artisanal and small-scale gold mining, mainly in low- and middle-income countries. Several industrial processes such as fuel combustion, cement production, metal smelting, large-scale gold mining with non-Hg methods as well as commercial Hg mining, has been emitted thousands of tons of Hg directly to the atmosphere since 1850. In addition to human related processes, several natural processes emit Hg to the environment, such as volcanic activity (geothermal vents, volcanoes) and emissions from natural enriched soils. Other types of Hg cycling mechanisms such as forest fires or oceanic emissions are considered mixed natural-anthropogenic sources. Primary sources transfer Hg from slow-cycling lithospheric reservoirs to the fast cycling atmospheric, oceanic and the terrestrial environments, thereby increasing the global pool of Hg in surface reservoirs. After deposition, Hg can be reemitted from the surface reservoirs to the atmosphere, therefore constituting a secondary source. Recycling from surface reservoirs results in an effective lifetime of 1.6 years before transfer to soil and deep ocean pools. Due to its volatility as Hg0 and the redox transformations of Hg in the environment, deposition and release are influenced by multiple environmental factors including seasonality, vegetation cover, temperature, light, moisture, atmospheric turbulence and the presence of reactants.