Multi-layered physical parameters govern mercury release from soil, its fate and potential for human health and ecological risk

Global mercury (Hg) management is an important issue for regulators and regional stakeholders, especially since the entry into force of the Minamata Convention in 2017. Although Hg has been used widely in pharmaceutical and industrial products, some forms of Hg present adverse risks for humans and ecosystems and, thus, Hg is considered both an air and soil pollutant. The UNEP Global Mercury Assessment Model (2013) clearly stated that it is important to understand the mechanisms of Hg release from soils because the amount emitted could be comparable to that released by human activities and from rivers and seas. Zero-valent gaseous elemental mercury (GEM) is the main component of gaseous Hg in the atmosphere and the most mobile species. To reduce the risk of human exposure to Hg, the mechanisms of GEM transport in the environment should be investigated and understood better.

A number of past studies have aimed to determine the relationship between GEM fluxes from soils and various environmental factors, both through laboratory experiments and field observations. These suggest that higher GEM fluxes are associated with higher soil and air temperature [1-3], increased solar irradiance [4,5], and with higher soil moisture [6,7]. However, it is not known which factors drive GEM flux and how to control conditions so as to suppress Hg emission from soil. The aim of this study was to investigate the main environmental factors influencing Hg release from soil, taking into account factors previously identified but not comprehensively interpreted.

Rigorous monitoring data was collected at two sites, tree-covered and shaded high-humidity forested areas (Site 1) and an open artificial soil environment with no trees (Site 2) in Miyagi Prefecture, Japan. This paper discusses the sites and methods used as well as the in depth analysis carried out. In the case of Site 2, the PCA and FA results have shown that atmospheric pressure, solar irradiance, and soil moisture are the primary factors driving GEM flux. In contrast, for Site 1, the analysis indicated that GEM fluxes were driven by as a cohesive group of factors rather than sequentially acting parameters. The results also suggest that it may be possible to estimate Hg emissions from soil by observing the magnitude of primary causality which could be useful for Hg management for the protection of human health and to minimise adverse ecological risk.

 

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