284
Trace Elements in Abiotic and Biotic Environments
The transformation between these species, as well as the formation of elemental Se
take place in all soils, however, under most conditions there are very slow processes.
–
Mobile anionic species that occur in soil solution are SeO 3
2– , SeO 4
2– , HSeO 4
– , HSeO 3 ,
HSeO 4
– , (Kabata-Pendias and Sadurski 2004). Some of these anions, mainly SeO 3
2– ,
are adsorbed by Fe oxides, and precipitate as Fe(SeO 3 ) 3 . Very weakly SeO
2
4
– is
adsorbed, especially at high soil pH. In acid soils Se is likely to occur as Se 4+ ,
strongly fixed by Fe compounds, and thus become slightly mobile. In general, mobile
and easy phytoavailable Se occurs in alkaline and well-aerated soils, thus in soils of
arid and semiarid regions.
The stability of Se–Fe compounds and Se adsorption by various metal hydroxides
and clay minerals control, to a high degree, Se behavior. Addition of PO 4 to soils may
increase Se mobility and thus its bioavailalbility. The phytoavailability of different
Se species in soils decreases in the following order:
Selenate > selenomethionine > selenocysteine > selenite > elemental Se > selenide
A close relationship between Se and organic C is common in most soils. Organic
matter has a tendency to form organometallic complexes, which remove Se from soil
solutions. Microbial processes in both, the formation and mineralization of organic
Se compounds (e.g., selenomethionine, selenocysteine) play a crucial role in the
Se cycling, and especially in its volatilization from Se-contaminated soils. These
processes are mainly the reduction of Se 4+ and Se 6+ , as well as methylation of Se.
Microbiota, reveal variable sensitivity to elevated Se contents, and its concentration
at 5 mM/L in soil solution may inhibit activity of soil enzymes (Nowak et al. vide
Kabata-Pendias and Mukherjee 2007). Therefore, organic amendments of soils may
significantly increase the rate of Se volatilization from soils. Microorganisms, especially Rhizobium sp. play an important role in Se volatilization. However, not all Se
species are available to microbial volatilization.
Selenium contents of soils and its behavior have received much attention, especially in countries where its deficiency in humans and animals has been recognized.
However, elevated Se contents of soils in some regions, due to both geochemical and
anthropological factors, are also of a great concern. Soils developed on seleniferous
parent material (e.g., Cretaceous limestone) and soil contaminated from irrigation
water or from coal power plants has also been a real environmental problem.
The water-soluble Se species are considered to be the fraction that is available
to plants, and usually there is an observed close relationship between Se content of
plants and its concentration in the soil solution, and in the diethylenetriaminepentaacetic acid extraction, which contain about 6% of its total contents (Borowska et al.
2012). However, some other Se species may also be phytoavailable, and there is a
calculation that about 45% of the total Se in soils may be taken up by plants (KabataPendias 2011).
The phytoremediation of Se-enriched soils has become recently a hot topic
of several experiments. Soils of regions with seleniferous parent materials and
Se-contaminated soils require alleviation. There are several publications presented
on “green technology of Se phytoremediation” (e.g., Banuelos 2001; Dhillon and
Dhillon 2009). The Se phytoremediation methods are based on the plant potential to
Trace Elements in Abiotic and Biotic Environments
The transformation between these species, as well as the formation of elemental Se
take place in all soils, however, under most conditions there are very slow processes.
–
Mobile anionic species that occur in soil solution are SeO 3
2– , SeO 4
2– , HSeO 4
– , HSeO 3 ,
HSeO 4
– , (Kabata-Pendias and Sadurski 2004). Some of these anions, mainly SeO 3
2– ,
are adsorbed by Fe oxides, and precipitate as Fe(SeO 3 ) 3 . Very weakly SeO
2
4
– is
adsorbed, especially at high soil pH. In acid soils Se is likely to occur as Se 4+ ,
strongly fixed by Fe compounds, and thus become slightly mobile. In general, mobile
and easy phytoavailable Se occurs in alkaline and well-aerated soils, thus in soils of
arid and semiarid regions.
The stability of Se–Fe compounds and Se adsorption by various metal hydroxides
and clay minerals control, to a high degree, Se behavior. Addition of PO 4 to soils may
increase Se mobility and thus its bioavailalbility. The phytoavailability of different
Se species in soils decreases in the following order:
Selenate > selenomethionine > selenocysteine > selenite > elemental Se > selenide
A close relationship between Se and organic C is common in most soils. Organic
matter has a tendency to form organometallic complexes, which remove Se from soil
solutions. Microbial processes in both, the formation and mineralization of organic
Se compounds (e.g., selenomethionine, selenocysteine) play a crucial role in the
Se cycling, and especially in its volatilization from Se-contaminated soils. These
processes are mainly the reduction of Se 4+ and Se 6+ , as well as methylation of Se.
Microbiota, reveal variable sensitivity to elevated Se contents, and its concentration
at 5 mM/L in soil solution may inhibit activity of soil enzymes (Nowak et al. vide
Kabata-Pendias and Mukherjee 2007). Therefore, organic amendments of soils may
significantly increase the rate of Se volatilization from soils. Microorganisms, especially Rhizobium sp. play an important role in Se volatilization. However, not all Se
species are available to microbial volatilization.
Selenium contents of soils and its behavior have received much attention, especially in countries where its deficiency in humans and animals has been recognized.
However, elevated Se contents of soils in some regions, due to both geochemical and
anthropological factors, are also of a great concern. Soils developed on seleniferous
parent material (e.g., Cretaceous limestone) and soil contaminated from irrigation
water or from coal power plants has also been a real environmental problem.
The water-soluble Se species are considered to be the fraction that is available
to plants, and usually there is an observed close relationship between Se content of
plants and its concentration in the soil solution, and in the diethylenetriaminepentaacetic acid extraction, which contain about 6% of its total contents (Borowska et al.
2012). However, some other Se species may also be phytoavailable, and there is a
calculation that about 45% of the total Se in soils may be taken up by plants (KabataPendias 2011).
The phytoremediation of Se-enriched soils has become recently a hot topic
of several experiments. Soils of regions with seleniferous parent materials and
Se-contaminated soils require alleviation. There are several publications presented
on “green technology of Se phytoremediation” (e.g., Banuelos 2001; Dhillon and
Dhillon 2009). The Se phytoremediation methods are based on the plant potential to