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Trace Elements in Abiotic and Biotic Environments
Especially important factor is Hg deposition in bottom sediments. Its content of
surface-bottom sediments of harbor in Klaideda (Lithuania) depends not only on its
concentration in water but also on the granulometric composition of sediments, and
is (in mg/kg, average and maximum, respectively) in sand 0.02 and 0.07 and in mud
0.04 and 0.15 (Galkus et al. 2012). Mercury contents in stream-bottom sediments of
National Park, Montgomery (Pennsylvania State) were, in 1995, within the range of
0.04–0.12 mg/kg (Reif and Sloto 1997).
Assessment limits for Hg in sediments are established as follows (in mg/kg):
effects range low, 0.15; effects range median, 0.71; probable effect level (PEL),
0.49; 2; 4 (EPA 2000, 2013). The Environment Canada sediment-quality guidelines (USGS 2001) gave the following values for Hg in the lake-bottom sediments
(in mg/kg): threshold effects level, 0.17; PEL, 0.49; and probable effect concentration, 1.06.
Median Hg concentration in both bottled and tap water of the EU countries is
<5 ng/L (Birke et al. 2010). Guideline value for inorganic Hg in drinking water is
established at 6 μg/L (WHO 2011a).
27.4 AIR
The worldwide mean Hg concentration in the atmosphere of remote regions varies
within the range of 0.01–0.06 ng/m 3 , whereas in urban/industrial areas it is between
0.17 and 38.0 ng/m 3 . Mercury content of air above Greenland varies from 0.04 to
0.08 mg/m 3 (Table 27.1).
Mainly, vapor-phase elemental Hg 0 (total gaseous mercury—TGM) is present in
the atmosphere. There is also HgCl 2 , but represents less than 5% of the total Hg
concentration. It may occur in both forms, as reactive gaseous mercury and total
particulate mercury. Metallic Hg 2+ present in air is relatively quickly deposited
within the distance of about 100 km from its sources, whereas Hg 0 is insoluble in
water and thus is transported, as particles, for long distances. Mercury adsorbed by
small air particles (10 μm) is more mobile in the atmosphere and easily inhaled by
people than that fixed by coarse particles (>10 μm). Mean Hg content of rainwater is
estimated at <0.002 μg/L.
Significant Hg sources in air are coal combustion and the inputs of various
industrial emissions. Global anthropogenic Hg fraction constitutes 40%–50% of
its total emission (Horvart et al. vide Kabata-Pendias and Mukherjee 2007). There
are also natural sources of Hg emission, which are from (1) the earth surface;
(2) previously deposited Hg waste; (3) volcanoes; and (4) geothermal activities.
Mercury is also emitted from the boreal forest and wetlands. The highest emissions
(up to 3.5 ng/m 2 /h) were observed at the forest floor with the moss and grass cover.
However, there was also noticeable uptake of Hg by the forest floor, depending on
weather conditions.
There is the lack of exact quantification of the Hg emission from natural
sources. However, there are suggestions that natural sources account for about
10%, estimated at 5.5–8.9  kt of Hg currently being emitted and re-emitted to
the atmosphere from all sources. Nevertheless, there are estimations that the Hg
deposition to the Greenland ice sheet is significantly influenced by anthropogenic