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Trace Elements in Abiotic and Biotic Environments
common in anaerobic, organic-rich environments (Gray et al. 2003). These processes
stimulate the reduction of cationic Hg 2+ to the elemental state, Hg 0 , which resulted in
the volatilization of Hg from media. It is relatively easily vaporized from surface soil,
mainly due to microbial processes. This process increased after water addition to soil.
Bacteria have an ability to adjust to increased Hg level in soils. Clay-mineral complexes on the surface of bacterial cell walls are apparently involved in mechanisms of Hg
resistance (Tazaki and Asada vide Kabata-Pendias 2011). Mercury methylated by microorganisms is more toxic to biota than its metallic forms (Perelomov and Chulin 2013).
Mercury may form various ionic species, both cationic and anionic; however, it is
not very mobile during weathering processes. Thus, Hg in soils is retained mainly as
slightly mobile organocomplexes. At soil, pH near neutrality predominates Hg(OH) 2 ,
which is readily adsorbed by both mineral and organic compounds.
Mercury contents in top soils greatly differ, depending on the soil origin and
pollution sources. Its highest concentration (up to 2695 mg/kg) is reported for soils
of Hg-mining district in Spain (Table 27.2). However, elevated Hg contents also are
seen in soils from vicinities of chloralkali plants, and in soils sludged or irrigated.
TABLE 27.2

Mercury Contamination of Surface Soils (mg/kg)

Site and Pollution Source
Country
Range/Maximum
Old mining area or ore deposit
Mercury-mining areas
Chloralkali or chemical industry
United Kingdom
Spain a
Canada
Egypt
France
0.2–3.4
0.13–2695
0.3–5.7
0.1–0.5
0.1–0.3
Urban garden and park
United Kingdom
Canada
Israel
3.8
0.02–1.14
0.04–0.08
Japan
United Kingdom
United States
0.06–0.24
0.25–15.0
0.6
Sludged or irrigated farmlands
Germany
Holland b
0.43–24
10.0
Hungary
Japan
Poland
0.02–0.15
0.29–0.71
0.12–0.35
Sweden
0.8
Application of fungicides
Canada
9.4–11.5
Sources: After Kabata-Pendias, A., Trace Elements in Soils and Plants, 4th ed., CRC
Press, Boca Raton, FL, 2011.
a Almaden mining district. Molina et al. (2006).
b Soils flooded by Rhine River water.