58
Trace Elements in Abiotic and Biotic Environments
In the European countries, atmospheric emission of Cd in 2001 was 24 t, of which
about 14 t was from metal production and refining, to comparing 158 t of Cd released
in 1990 in these countries, which is the evident result of good effects of the technology in nonferrous smelters.
Cadmium and its compounds may be in the atmosphere in both forms, suspended
particulate matter and vapor. Therefore, it is very easily transported, even for a long
distance. Cd particles greater than 10 μm fall on soils around their released sources.
However, there is still Cd deposition from the long, transboundary air transport.
9.5 PLANTS
Cadmium is taken up by plants passively, but may be also absorbed metabolically.
Often, there is a linear relationship between Cd in plants and its concentration in
the growth media. Soil pH is considered to be the major soil factor controlling Cd
uptake. In most cases, the most phytoavailable Cd is in soils at pH ranging from 4.5
to 5.5. However, when Cd is present in complexes and/or chelates, its uptake is not
controlled by soil pH. Also, low Eh values (about 20 V) of soils decrease solubility
and thus the availability of Cd. Not only soluble Cd species are taken up by plants
but also Cd fixed by the Fe–Mn oxide fractions is easily available to some plants
(Wang et al. 2012).
Several soil properties control Cd solubility, and therefore predicting its phytoavailability is not simple. Nevertheless, most experiments have indicated that
plant Cd is a function of soil Cd (Verma et al. 2007). Liming of soils gives variable results in minimizing Cd uptake. P fertilizers always increase Cd uptake. Also,
N fertilizers increase Cd concentration in soil solution and thus its content in wheat
grains (Wangstrand et  al. 2007). Soil salinity stimulates the formation of several
Cd–Cl complexes, which are easily soluble and easy phytoavailable. Cadmium from
some composts and sewage sludge may also be easily available to plants (Chaudri
et  al. 2007). Its availability is under the variable impact of rhizosphere bacteria
(Dell’Amino et al. 2008).
Distribution of Cd within plant organs is different, but most often illustrates its
transport from roots to tops, in particular, to leaves. However, it may also be an
effect of the atmospheric Cd deposition. Significant source of Cd from air is illustrated by its higher content in caps (5.22  mg/kg) than in stalks (1.86  mg/kg) of
mushrooms (Boletus edulis) from Magurski National Park in Poland (Sembratowicz
and Rusinek-Prystupa 2012). The mushrooms, common chanterelles (Cantharellus
cibarius), grown in mountains contain higher amounts of Cd, 0.88 mg/kg, than those
grown in the Baltic Sea coast, 0.43 mg/kg (Falandysz et al. 2012).
Mean Cd contents of cereal grains range from 5.6 to 32 μg/kg, of barley and wheat,
respectively (Eriksson 2001a). Fodder plants contain much more Cd, within the
range of mean values (in μg/kg): in clover, 80–460 and in grass, 70–400.
Biochemical functions of Cd are variable; it has a strong affinity to sulfhydryl and
phosphate groups, to concentrate in proteins compounds, and to accumulate in phytochelatin complexes. It has a toxic impact on plants metabolism, disturbing enzyme
activities. It reduces ascorbate and glutathione levels, inhibits chlorophyll formation and affects cell acidosis (Nocito et  al. 2008). In general, symptoms induced