Direct conversion of insoluble HgS species to MeHg in anaerobic soils is generally considered to be low, although this condition may change if environmental conditions favour HgS complexation [103]. Redox potential also appears to be a key factor, as subtoxic and mildly reducing conditions appear to favour high methylation rates of Hg2+, while anoxic and strongly reducing conditions may lead to increased sulphide concentrations, possibly preventing the availability of Hg2+ for methylation of some methylating bacteria, including SRB (sulphate-reducing bacteria, for example, Desulfobacter sp.) and some that increase the availability of Hg2+. for methylation (e.g. deltaproteobacteria or clostridia) [104, 105]. It is very difficult to estimate mercury emissions from plants, and these emissions occur mainly in the form of mercury [78,79,80]. Ericksen et al. [81] proposed the following hierarchy of environmental parameters influencing mercury flow: While techniques such as XAFS identify mercury species present in a source, chemical extraction and thermal decomposition techniques classify mercury into behavioural classes that influence our understanding of bioavailability. In general, these methods measure the extractability of mercury using a range of leaching or heating treatments. Extraction solutions and specific temperatures are often substitutes for expected environmental and biological conditions. Chemical and thermal mercury extraction measurements have been conducted as part of the assessment of many contaminated sites (Ecology and Environment, 2015; U.S. EPA, 2015; U.S. EPA, 2017); However, there is still no direct link between these measurements and MeHg production. Selin H, Keane SE, Wang S, Selin NE, Davis K, Bally D (2018) Linking science and policy to support the implementation of the Minamata Convention on Mercury.
Ambio 47:198–215. doi.org/10.1007/s13280-017-1003-x In recent decades, extensive scientific knowledge has been gained on the sources and emissions of mercury, its pathways and cycle in the environment, human exposure, and effects on the environment and human health [2]. Mercury is the only element of the periodic table that has its own environmental convention, namely the Minamata Convention on Mercury, which highlights the importance of the issue of mercury pollution [3]. Mercury is recognized as a toxic, persistent and mobile contaminant; It is not degraded in the environment and becomes mobile due to the volatility of the element and several of its compounds. Atmospheric mercury contamination remains one of the most important environmental problems in the modern world. The general conclusions were drawn from a literature review and presented in this paper. Humic acid affects the transport and conversion of mercury in soil-plant systems, especially in soils with low clay content. Humic acid reduces the amount of mercury available in the soil and prevents mercury from being transported to plants or removed from the soil. Leaching can cause mercury to enter natural water systems under normal environmental conditions. In practice, humic acid can be used to control the transport of mercury through food chains from soils heavily contaminated with mercury [145].
Different forms of atmospheric mercury can be deposited on surfaces by wet and dry processes. These forms can be sequestered in terrestrial compartments or emitted into the atmosphere, the relative importance of these processes depending on the form of mercury, surface chemistry and environmental conditions. Many models assume that the net GEM (gaseous elemental mercury) exchange with ground surfaces is zero; However, as discussed below, some components are absorbed into foliage during the growing season and accumulate in soils [59]. Smith-Downey et al. [60] Estimated that mercury bypass associated with the decomposition of soil organic carbon pools and the subsequent release of absorbed mercury into soil organic matter is greater than 700 t/year, reflecting the large reserve of mercury stored in terrestrial ecosystems worldwide (over 240 kgt). Overall, this study estimates that 56% of mercury deposited in terrestrial ecosystems is re-emitted. Similarly, Graydon et al. [61] found that 45-70% of isotopically deposed HgII wet in a forest watershed was released to the atmosphere after one year. Other chemical extraction techniques use multiple steps to estimate several biogeochemically relevant mercury fractions.
A common (and commercially available) technique based on the methods described in Bloom (2003) is often referred to as selective sequential extraction (SSE, see SI Table S1). Different extraction solutions are used to estimate six fractions of Hg. Fraction 0 (F-0) indicates the presence of Hg0; fraction 1 (F-1) estimates water-soluble mercury; fraction 2 (F-2) appreciates the acid-soluble or other acidic environment of the human stomach; Fraction 3 (F-3) estimates the mercury complexed by NOM; and fractions 4 and 5 (F-4, F-5) estimate mineral-bound Hgs and other highly complex Hgs. Fractions 0–3 can be interpreted as forms of mercury available in the environment; while the F-4 and 5 are more unruly and can be considered unavailable. Comparisons between ESS and XAFS show good agreement between unruly fractions (F-5) and cinnabar and metacinnabar, but are more divergent in the identification of soluble forms (Bernaus et al., 2006; Kim et al., 2003; Terzano et al., 2010). ESS fractions may be linked to associated toxicity criteria in risk assessments with routes of exposure (SI Table S2). However, risk assessments must take into account the potential transformation between forms, in particular F-0 to F-3. ESS (as well as XAFS analyses) can be performed on sieved samples to determine how mercury speciation changes with amplification size, as well as the mobility of different forms of mercury for off-site transport (Lowry et al., 2004). Aryeh Feinberg *a, Thandolwethu Dlamini a, Martin Jiskra b, Viral Shah c and Noelle E. Selin *ad aInstitute for Data, Systems, and Society, Massachusetts Institute of Technology, Cambridge, MA, USA.
Email: arifein@mit.edu; selin@mit.edu bEnvironmental Geosciences, University of Basel, Basel, Switzerland cHarvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, United States dDepartment of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA Atmospheric mercury contamination remains one of the most important environmental problems in the modern world. The following general conclusions can be drawn from this literature review and are accompanied by the authors` critical comments: Studies have successfully used mercury isotopes to detect industrial sources of mercury in aquatic ecosystems (Donovan et al., 2013; Feng et al., 2010; Foucher et al., 2013; Foucher et al., 2009; Gehrke et al., 2011a; Wiederhold et al., 2013; Yin et al., 2013b). Mercury can be printed with different isotopic signatures from different processes, such as the use of mercury catalysts that are retained in waste or concentrated mercury releases.