Citrate assisted phytoextraction of uranium by sunflowers: Study of fluxes in soils and plants and resulting intra-planta distribution of Fe and U

This study aimed to determine how the citric acid assisted phytoextraction of uranium (U) by sunflowers impacted on the remobilisation of U in soil, its subsequent transfer to plants and its further distribution intra-planta. Consequences of the flux of nutrient elements [iron (Fe) and zinc (Zn)] able to interfere with U during this process were also specifically addressed. A U-contaminated soil receiving different citric acid treatments in terms of dose delivered and frequency of delivery was studied. Dynamics of remobilisation in soil were assessed using DGT (Diffusive Gradient in Thin-film) measurements, and phytoextraction experiments were conducted in a Rhizoplan device. All treatments induced a remobilisation of U and Fe from the soil solid-phase to the soil solution. Consequently, sunflower uptake of U was greatly enhanced, whereas the uptake of Fe was not affected - in accordance with the high regulation of this nutrient in the plant. As for U, the Zn uptake increased due to the citric acid treatment. The DGT-measured concentration correlated well with the concentration taken up by plants for U. Nevertheless, under all conditions, U fluxes to DGT were higher than U fluxes to plants, suggesting that DGT did not mimic the plant uptake mechanism for U. There was no correlation found for Fe, due to its plant uptake regulation. Distribution of these elements in planta was strongly impacted by citric acid, with an increase in translocation from root-to-shoot of both U and Fe, whereas Zn remained mainly in the roots. Such an increase was expected for U but was very surprising for Fe, suggesting that the presence of U in plants may have interfered with mechanisms that regulate Fe homeostasis. (C) 2011 Elsevier B.V. All rights reserved.