143
by roots can also modify uranium bioavailability. Complexation reaction with organic
acids tends to increase uranium solubility in soil (Boghi et al. 2018). Citrate exudation can enhance uranium uptake and translocation from roots to shoots and leaves
(Laurette et al. 2012b; Henner et al. 2018). Phytoremediation experiments also
reported an increase in uranium concentration in plants and translocation from root to
shoots (Mihalík et al. 2010, 2012), although not all plant species showed the same
behavior. Transfer factor increased for root and leaves for willow; while for sunflower
an increase for leaves and a decrease for roots were reported (Mihalík et al. 2010).
Uranium complexation with phosphates can reduce its concentration in plant tissues by precipitation and adsorption of uranium-rich clusters in epidermal cells
(Laurette et al. 2012a, 2012b). Laboratory experiments showed the possibility of
biomineralization of U(VI) phosphate as a result of microbial phosphatase activity
but only with pure cultures (Beazley et al. 2011). Fungi can also precipitate uranium
phosphate when growing on an organic source of phosphorus (Liang et al. 2015).
Fungal phosphatase can hydrolyze organic phosphorus, releasing inorganic phosphate which can form uranyl complexes and later precipitate. Fungi present in soil
can also enhance uranium uptake by plants, especially arbuscular mycorrhizal fungi
associated with plants (Davies et al. 2015, 2018; Boghi et al. 2018). On the other
hand, no correlation between uranium in roots and percentage of arbuscles, vesicles,
or hyphae were reported (Davies et al. 2018).
4 Conclusion
The analysis of transfer processes in the environment, and especially involving
plants, is essential to assure an adequate radiological protection of man and the
environment. In this chapter, a review of the main factors influencing uranium transfer from soil to plant was carried out, showing that:
• The range of variation of transfer factors parameters for U and F v presents a
variation of 5–6 orders of magnitude worldwide and lower than those for Cs and
Sr.
• U distribution is heterogeneous within plant, accumulating preferentially in
roots.
• As U is naturally occurring, and therefore constituent of some minerals, it is
mainly associated to residual or strongly bonded fraction in sequential extraction
procedures.
• Soil amendments using citric acid enhance uranium uptake by plants, whereas
when phosphate is added, U can become immobilized in soil.
• Organic matter in soil can enhance U uptake by plants, especially in those in
symbiosis with arbuscular mycorrhyzal fungi.
Acknowledgement This work was partially made possible by the financial support granted to the
LARUEX research group (FQM001).
Factors Influencing the Soil to Plant Transfer of Uranium
by roots can also modify uranium bioavailability. Complexation reaction with organic
acids tends to increase uranium solubility in soil (Boghi et al. 2018). Citrate exudation can enhance uranium uptake and translocation from roots to shoots and leaves
(Laurette et al. 2012b; Henner et al. 2018). Phytoremediation experiments also
reported an increase in uranium concentration in plants and translocation from root to
shoots (Mihalík et al. 2010, 2012), although not all plant species showed the same
behavior. Transfer factor increased for root and leaves for willow; while for sunflower
an increase for leaves and a decrease for roots were reported (Mihalík et al. 2010).
Uranium complexation with phosphates can reduce its concentration in plant tissues by precipitation and adsorption of uranium-rich clusters in epidermal cells
(Laurette et al. 2012a, 2012b). Laboratory experiments showed the possibility of
biomineralization of U(VI) phosphate as a result of microbial phosphatase activity
but only with pure cultures (Beazley et al. 2011). Fungi can also precipitate uranium
phosphate when growing on an organic source of phosphorus (Liang et al. 2015).
Fungal phosphatase can hydrolyze organic phosphorus, releasing inorganic phosphate which can form uranyl complexes and later precipitate. Fungi present in soil
can also enhance uranium uptake by plants, especially arbuscular mycorrhizal fungi
associated with plants (Davies et al. 2015, 2018; Boghi et al. 2018). On the other
hand, no correlation between uranium in roots and percentage of arbuscles, vesicles,
or hyphae were reported (Davies et al. 2018).
4 Conclusion
The analysis of transfer processes in the environment, and especially involving
plants, is essential to assure an adequate radiological protection of man and the
environment. In this chapter, a review of the main factors influencing uranium transfer from soil to plant was carried out, showing that:
• The range of variation of transfer factors parameters for U and F v presents a
variation of 5–6 orders of magnitude worldwide and lower than those for Cs and
Sr.
• U distribution is heterogeneous within plant, accumulating preferentially in
roots.
• As U is naturally occurring, and therefore constituent of some minerals, it is
mainly associated to residual or strongly bonded fraction in sequential extraction
procedures.
• Soil amendments using citric acid enhance uranium uptake by plants, whereas
when phosphate is added, U can become immobilized in soil.
• Organic matter in soil can enhance U uptake by plants, especially in those in
symbiosis with arbuscular mycorrhyzal fungi.
Acknowledgement This work was partially made possible by the financial support granted to the
LARUEX research group (FQM001).
Factors Influencing the Soil to Plant Transfer of Uranium