Interactions of Mercury and Selenium in River System
Although mine-waste calcines were observed to be sources of selenium (Se) in the downstream areas, similar to mercury (Hg) (Zhang et al. 2010b , c , 2014 ), the correlation between Se and Hg in the dissolved phase in river water was not significant (p >
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Interactions of Mercury and Selenium in River System
Although mine-waste calcines were observed to be sources of selenium (Se) in the downstream areas, similar to mercury (Hg) (Zhang et al. 2010b, c, 2014), the correlation between Se and Hg in the dissolved phase in river water was not significant (p [ 0.05; Fig. 7.1). This result was likely affected by the enhanced Se content in the downstream area contributed by the Se-enriched groundwater (Zhang et al. 2014). The Se content in river water affected by mining and retorting activities in Wanshan was controlled by multiple dynamic factors, e.g., combined point-source pollution (primarily mine-waste calcines) and non-point-source pollution (surface run-off and groundwater, etc.); therefore, the precipitation of possible interactions between Hg and Se, if present, may be hidden behind the detectable phenomena. In present study, based only on the Hg and Se in the dissolved phase of river waters, we cannot draw any conclusion regarding the potential interactions of Se and Hg in river waters. However, it appears that the elevated selenate and selenite (80 %) in the river water in Wanshan are controlled by the alkaline conditions (Zhang et al. 2014) and the formation of a considerable amount of Hg–Se insoluble complexes is likely to be insignificant, if it exists. Therefore, a negligible influence from the formation of inert Hg–Se complexes on the transport of Se or Hg in the river systems may be expected. The river waters in Wanshan that have been impacted by Hg mining and retorting activities are used by the local farmers as the main sources of irrigation for a large quantity of riparian rice paddies, which may cause contamination by Se in addition to mercury in the agriculture system. For the paddy soil system, one simplified method used to identify the geochemical evolutionary trends of Hg and Se species and possible interactions in aqueous solution is an Eh-pH diagram. The pH values in the rhizosphere in the study area generally ranged between 6.2 and 7.5 (Zhang et al. 2010a). The Eh values in the rhizosphere of the rice paddy are well known to be generally lower than -0.2 V under prolonged flooding and can reach over 0.4 V during the water leakage period (Rostaminia et al. 2011). According to the Eh-pH diagrams for Se versus Hg (Fig. 7.2), Hg0 and Se0 were H. Zhang, Impacts of Selenium on the Biogeochemical Cycles of Mercury in Terrestrial Ecosystems in Mercury Mining Areas, Springer Theses, DOI: 10.1007/978-3-642-54919-9_7, Springer-Verlag Berlin Heidelberg 2014
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7 Interactions of Mercury and Selenium in River System
Fig. 7.1 Relationship between Se (tot) and Hg (tot) in filtered (0.45 lm) water samples collected from rivers in Wanshan (Reprinted from Zhang et al. (2014), with permission from Elsevier)
Fig. 7.2 The thermal dynamic equilibrium phase (Eh-pH) diagrams of Hg versus Se [after Hem (1970) and Wen et al. (2006)]
the most thermodynamically stable species in the rhizosphere environment in the study area (forms of Hg2+ and Se2- could also occu
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