Mercury Cycling in Soils: Existing Knowledge and Areas of Consideration.

Mercury (Hg) is a global contaminant and threatens the health of humans and wildlife throughout the world. Soils are critical in the global Hg cycle; they are a source for water bodies and a sink for the atmosphere. Understanding where and how Hg accumulates in soil is essential for addressing human and wildlife health concerns and adequately modeling its global cycle. Although determining Hg methylation and its movement to aquatic systems has been paramount, alternative pathways such as terrestrial bioaccumulation or crop uptake may be underestimated and represent important fluxes to humans and wildlife. Mercury cycling in soils is a complex problem, encompassing processes from the atomic to landscape scale. Thus, it requires many divisions of soil science to adequately address this issue. At the atomic scale, sorption by organic compounds (e.g. thiol groups) and inorganic compounds (e.g. Fe oxides) can affect Hg accumulation. At the pedon scale, redoximorphic conditions can increase the mobility of Hg and production of Methyl-Hg. At the landscape scale, the variation in geomorphic positions can affect deposition of Hg and its retention in organic horizons. These are important aspects current models estimating the global Hg cycle often do not take into account. Utilization of new methods such as Hg isotopes may help elucidate the pathways. Quantifying and synthesizing this information is necessary to detail hazards to organisms and the role of soils in the global Hg cycle.