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Phytoextraction of Radionuclides from Contaminated Soil
Reference
Song, N., Zhang, X., Wang, F., Zhang, C. and Tang, S. 2012. Elevated CO2 increases Cs uptake and alters microbial communities and biomass in the rhizosphere of Phytolacca americana Linn (pokeweed) and Amaranthus cruentus L. (purple amaranth) grown on soils spiked with various levels of Cs. Journal of Environmental Radioactivity 112: 29-37.

Background
The authors write that "industrial activities, nuclear weapons production and testing, and nuclear accidents over the past seventy years have led to an increase in the soil concentrations of some radionuclides," and they say that local radionuclide contamination often poses a long-term threat to human health through the food chain." Hence, there is good reason to consider how best to remedy this situation.

What was done
In light of the fact that the behavior of radiocesium in nature follows that of stable cesium (Cs), and that stable Cs can thus be used as an analogue of radioactive Cs isotopes (Uchida et al., 2009), Song et al. employed open-top chambers to study the effects of elevated atmospheric CO2 concentration (860 ppm vs. the 360 ppm of ambient air) on the growth and development of pokeweed (Phytolacca americana) and purple amaranth (Amaranthus cruentus) and their rate of uptake of stable Cs from the soil of the pots in which the two species grew for a period of 52 days, one plant each to single 15-cm-diameter by 12-cm-high pots filled with a sandy loam soil to which cesium chloride (CsCl2) was added to give five different levels of Cs contamination: 0, 100, 300, 500, and 1000 mg Cs/kg soil.

What was learned
The five Chinese researchers report that "both plant species grown under elevated CO2 showed shoot and root dry weight biomass stimulation ranging from 6 to 102% and an increase of shoot and root Cs content ranging from 6 to 150%."

What it means
Song et al. conclude that their experiment provides more lines of evidence that the CO2-triggered hyper-accumulation of Cs "may be developed as a potential useful phytoremediation tool to clean-up soils contaminated with radiocesium," noting that the technique has "a definite potential to remove more radionuclides from soil" and could act as a low-cost method of phytoextraction.

Reference
Uchida, S., Tagami, K., Shang, Z.R. and Choi, Y.H. 2009. Uptake of radionuclides and stable elements from paddy soil to rice: a review. Journal of Environmental Radioactivity 100: 739-745.

Reviewed 23 January 2013