200
Trace Elements in Abiotic and Biotic Environments
of Pediatrics have recently accepted the addition of thimerosal to various vaccines
for children.
Galistan, an alloy of Ga, In, and Sn, or alternatively, digital thermometers, now
replaces the Hg used in traditional Hg thermometers. Hg-cell technology is being
replaced by newer diaphragm and membrane-cell technology at chloralkali plants.
Light-emitting diodes that contain In in lamps, batteries with Li, Ni–Cd, and Zn batteries, are presently substitutes for Hg instruments.
Mercury has been known since prehistrorical times, and was used by alchemists
in China since 2000 BC. For over a century, it has been known as an environmental pollutant. Released Hg with industrial wastewater in Minamata (Japan) in 1959
resulted in neurological damage of many people. Effects of Hg uses are still observed.
Increased Hg load into the environment due to its use in Au mines became a
real environmental concern (mainly in Amazonian region and Siberian subregion).
All metals can form amalgams with Hg. The amalgam Au + Hg used in the extraction
of Au from ore is of environmental risk in the Au-mine districts. There is an estimation that about 1000 t Hg/yr is used and lost by artisanal miners.
Mercury is considered a global, hazardous pollutant, which is widespread, mobile
and easily bioaccumulated. Its emission from various industries, and coal combustion is still of a great environmental concern. Current, worldwide anthropogenic Hg
sources is calculated at about 2909 t/yr, and its emission from fossil-fuel-fire power
plants is given as 1422 t/yr (Pirrone et al. 2009).
27.2 SOILS
The worldwide average content of Hg in soils is estimated at 1.1 mg/kg, within the range
of 0.01–1.5 mg/kg; however, it seldom exceeds 1 mg/kg (Randall and Chattopadhyay
2004). Higher Hg contents are in heavy loamy soils (Table 27.1). Its lowest contents
are reported for soils of Sweden, 0.043 mg/kg (Kabata-Pendias 2011). The background
levels of Hg in soils are not easily established, due to the widespread Hg pollution. Soil
quality Hg levels are estimated, based on various criteria, within the range of 1–23 mg/kg.
The contamination of soils (Dutch List 2013), following Hg concentrations in soils and
groundwater, is established (in mg/kg and μg/L) as follows: uncontaminated, 0.5 and
0.2; medium contaminated, 2 and 0.5; and heavily contaminated, 10 and 2.
Mercury contents of virgin soils are inherited mainly from the parent rocks.
In some regions, however, degassing and thermal activity of the Earth may be its second sources. Soils of volcanic areas contain Hg up to 7.45 mg/kg, at Mt. Etna (Italy),
and up to 0.23 mg/kg at Mt. St. Helen (United States). Mercury in soils of municipal lawns in Wrocław City (Poland) vary within the range of 0.05–1.14 mg/kg, and
does not exit standard content established for urban soils, at 2.0 mg/kg (Dradrach
and Karczewska 2013). Agricultural top soils of Spain contain Hg within the range
of 0.001–0.22 mg/kg (Rodrigues et al. 2008). The maximum Hg contents of some
Brazilian soils vary from 1.6 to 29.1 mg/kg (Melo 2012).
Mercury is highly associated with soluble organic matter (SOM) and S levels in
soils, and thus it is concentrated mainly in surface layers. Especially, raw humus material reveals a great capacity for binding Hg, which is the main source of atmospheric
deposition. In all soils, its highest sorption is at pH range from 4 to 5. Soil sorption