Phytoremediation of Radionuclides

 

Plant Species Used for Phytoremediation of Radionuclides

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A large amount of research has focused specifically on cesium and strontium due to their prevalence from nuclear-related activities. This portion of the website only includes research upon cesium and the plant species that have been used to study the uptake of cesium from soils. Additional information about other radio isotopes can be found in the references cited.

Cesium
Cesium-137 (137Cs) is commonly used in phytoremediation research since it is a product of nuclear fission and has been relatively widely distributed by nuclear tests, nuclear power generation and accidents, such as the 1986 Chernobyl incident (Entry and Watrud 1998, Negri and Hinchman 2000, Beresford 2005). A primary concern with radiocesium contamination is the uptake and bioacculumation of the radionuclide in the food chain and potential effects on human health (Entry et al. 1996).
http://www.uga.edu/srel/Snapshots/phyto_fig.jpg
Cesium can be uptaken by many plant species, but there is great variation in the plant tissue concentrations and total amount of Cs uptaken in different plant species and under different soil conditions (Broadley and Willey 1997). Many factors have been shown to decrease the uptake of 137Cs by plants, including: finer soil textures (clays), higher organic matter content, and greater phosphorus levels (Negri and Hinchman 2000). Reductions of potassium (K) in the soil resulted in increased Cs uptake by plants (Broadley and Willey 1997, Gouthu et al. 1997). Based upon this information, the physical and biogeochemical composition of the soils should not be ignored in any phytoremediation project. The role of microorganisms in cesium uptake is not well understood, but one study found that inoculation with VAM fungi (vesicular arbuscular mycorrhizae) increased the uptake of cesium in sweet clover and sorghum (Rogers and Williams 1986). In order for the phytoremediation of soils contaminated with Cs or other radionuclides to be successful, it is essential to understand the interactions between the plants, soils, and microbes, especially under different nutrient and climate regimes (Camps et al. 2003).

The following list includes a few of the plant species known to accumulate radiocesium:

Amaranthus retroflexus (redroot pigweed)(Negri and Hinchman 2000)
Beta vulgaris (beet) (Negri and Hinchman 2000)
Brassica juncea (Indian mustard)(Negri and Hinchman 2000)
Cucumis sativus (cucumber)(Gouthu et al. 1997)
Chenopodium quinoa (quinoa)(Negri and Hinchman 2000)
Helianthus annuus (annual sunflower)(Soudek et al. 2004, Soudek et al. 2006a, Soudek et al. 2006b, Tome et al. 2008)
Lycopersicon esculentum (tomato)(Gouthu et al. 1997)
Melilotus officinalis (sweet clover)(Rogers and Williams 1986, Negri and Hinchman 2000)
Panicum virgatum (Alamo switchgrass)(Entry and Watrud 1998)
Phragmities australis (reed)(Soudek et al. 2004)
Populus simonii (poplar)(Soudek et al. 2004)
Salsola kali (Russian thistle)(Negri and Hinchman 2000)
Sorghum sudanense (sorghum)(Negri and Hinchman 2000)
Vetiveria zizanoides (Vetiver grass)(Singh et al. 2008)

Comparison of cesium uptake by plant taxa
A survey of radiocesium uptake by 30 plant species found that taxa in the Chenopodiaceae (specifically varieties of Beta vulgaris ssp. vulgaris) had the greatest Cs concentrations in fresh tissues and removed the most Cs from the soil (Broadley and Willey 1997). Grasses had the lowest Cs concentrations and uptake in the study. Broadley and Willey (1997) correlated Cs concentrations to shoot weight and therefore postulated that faster growing plants were better accumulators of radiocesium. Additionally, since many Chenopodiaceae are halophytic plants, the researchers suggested more study into the mechanisms for salt tolerance and the potential link to the uptake of radionuclides. Another survey of radionuclide uptake by plants found that tomato, chard, and cucumber had the greatest uptake rate based upon plant dry weights (Gouthu et al. 1997).