Germanium [Ge, 32]
127
water, Ge ranges from 0.001 to 0.08 μg/L, at the world mean content at 0.007 μg/L
(Gaillardet et al. 2003). According to these authors, the riverine flux of Ge is 0.25 kt/yr.
In aquatic environments, Ge occurs as cationic species, but more commonly as
2
complex anions such as HGeO 2 , HGeO 3 , and GeO 3
. Also, organic Ge species,
mainly as methylated forms, are present in water, and apparently dominate over
mineral forms. Amounts of the MM–Ge and DM–Ge forms in oceans vary depending on the water salinity. These Ge species are rare in river water. Similar to Si and
Al, natural Ge compounds tend to be insoluble in water.
Median Ge concentration in the bottled water of the EU countries is 0.029 μg/L,
and is a bit higher than those in tap water, 0.011 μg/L (Birke et al. 2010).
17.4 AIR
Main sources of Ge in the atmosphere are from coal-fired plants, metallurgical
industries, and waste incineration. Its emission from coal burning in the United
Kingdom was estimated at about 2 kt/yr (Kabata-Pendias and Mukherjee 2007). It is
also discharged in air from stack gases.
The best indicator for Ge concentrations in air is its content in mosses. Moss
samples collected in 1975 and 2000 in South Sweden contained Ge on average levels
at 0.091 and 0.015 mg/kg, respectively (Rühling and Tyler 2004). Mosses sampled in
Norway, during 1990–1995, contained Ge within the range of 0.24–11 mg/kg (Berg
and Steinnes 1997).
17.5 PLANTS
Germanium is not thought to be an essential element for plants. However, it is
absorbed by plants relatively easily, possibly in the form GeO 2 . Its average content in
various plants is estimated at 20 mg/kg. In food plants, Ge concentrations vary from
10 to 754 mg/kg, with the lowest in barley grain, and the highest in garlic. However,
there are also quite different values of Ge in food plants from the Central American
region, within the range of <0.01–<0.1 (Duke 1970).
Although Ge is toxic to plants, some plants (e.g., rice) may accumulate high Ge
amount (up to 1% AW). Apparently, there is an interaction between Ge and Si, and
plants needing Si for the growth are sensitive to Ge. There is evidence that even a low
concentration of Ge inhibits the germination and growth of some plants.
Increased levels of Ge in some plants may be due to aerial pollution. This is well
illustrated by increased levels of Ge in leaves of two kinds of trees growing in the mountains and near streets of the Wrocław City (Poland), from 12–14 to 100–108 mg/kg,
respectively (Sarosiek et al. vide Kabata-Pendias 2011).
17.6 HUMANS
Germanium amount in human body is 5 mg, of which in blood 0.4 mg/L and in tissue 0.1 mg/kg (Emsley 2011). Its absorption from gastrointestinal tract is believed to
be rapid and complete, followed by a rapid excretion, mainly with urine. There is no