Research on Transfer Parameters and Health Risk Assessment of Uranium and ²²⁶Ra in Okra and Peanut

Radioactive contamination of soil in uranium mining areas and its impacts on crop safety constitute a critical environmental concern. Nevertheless, merely analyzing the concentrations of radionuclides in crops and their rhizosphere soil is insufficient to comprehensively assess the potential threats to human health. In this study, two locally prevalent crops—okra and peanut—were cultivated in soils with varying contamination levels within a uranium mining area. The uranium concentrations and specific activities of ²²⁶Ra in the rhizosphere soil, as well as different plant tissues (roots, stems and leaves, edible parts) of the two crops were determined separately. Transfer factors (TF₁, TF₂, TF₃) of the two radionuclides from soil to crop roots, stems/leaves and edible portions were calculated accordingly. Furthermore, two distinct evaluation approaches, namely the pollution load index (P_LI) method and a health risk assessment model, were adopted to comprehensively characterize the contamination status of okra and peanuts. Key findings of this study are summarized as follows. The concentrations of uranium and ²²⁶Ra in soils of both crop-growing areas are markedly higher than the local geochemical background values. Uranium and ²²⁶Ra exhibit opposite translocation patterns within plants: Uranium is largely retained in root tissues with limited upward translocation, while ²²⁶Ra possesses high mobility and preferentially accumulated in edible tissues, imposing greater potential risks via dietary intake. Except for okra grown in lightly contaminated plots, the contents of uranium and ²²⁶Ra in the edible parts of all other crop samples exceed the limit values specified in the Chinese national standard Limited Concentrations of Radioactive Substances in Foods (GB 14882-1994). In addition, both peanuts and okra suffer severe overall radioactive contamination, with their P_LI values falling into the extreme pollution grade. Health risk assessment results indicate that peanuts cultivated in heavily uranium-contaminated plots poses non-carcinogenic risks, with hazard quotient (HQ) values exceeding the threshold of 1.0. The total carcinogenic risk of peanuts is higher than the negligible risk level (1×10⁻⁶) set by the United States Environmental Protection Agency (USEPA), yet lower than both the unacceptable risk threshold (1×10⁻⁴) and the reference value (5×10⁻⁵) recommended by the International Commission on Radiological Protection (ICRP). In comparison, okra from all experimental plots presents acceptable non-carcinogenic and carcinogenic risks. In conclusion, the results demonstrate that although both crop species are subjected to significant soil-derived radioactive contamination, the divergent translocation behaviors of uranium and ²²⁶Ra lead to distinctly different exposure risks. Special caution is required for peanut cultivation and rigorous monitoring should be implemented in heavily polluted zones to guarantee food safety.