Effect of low molecular weight organic acids on the uptake of ²²⁶Ra by corn (Zea mays L.) in a region of high natural radioactivity in Ramsar-Iran

To study the benefit of including citric and oxalic acid treatments for phytoremediation of ²²⁶Ra contaminated soils a greenhouse experiment with corn was conducted. A soil was sampled from a region of high natural ²²⁶Ra radioactivity in Ramsar, Iran. After cultivation of corn seed and using organic acid treatments at 1, 10 and 100 mM concentrations, plants (shoots and roots) were harvested, digested and prepared to measure ²²⁶Ra activity. Simultaneously, sequential selective extraction were performed to estimate the partitioning of ²²⁶Ra among geochemical extraction. Results showed that the maximum uptake of ²²⁶Ra in plants was observed in citric acid (6.3%) and then oxalic acid (6%) at 100 mM concentration. These treatments increased radium uptake by a factor of 1.5 than the control. Enhancement of radium uptake by plants was related to soil pH reduction of organic acids in comparison to control. Also, the maximum uptake of this radionuclide in all treatments was obtained in roots compared to shoots. ²²⁶Ra fractionations results revealed that 91.8% of radium was in the residual phase of the soil and the available fractions were less than 2%. As the main percent of ²²⁶Ra was in the residual phase of the soil in this region, it seems that organic acids had not significant effect on the uptake of ²²⁶Ra for phytoremediation by corn in this condition.