## 3 Results and Discussion
### Transfer Factors of \({}^{238}\)U and \({}^{226}\)Ra between Soil and Studied Plants  
Figure 6 shows the transfer factors (TF) of \({}^{226}\)Ra and \({}^{238}\)U for the four species studied. On the other hand, Figure 6 presents a biplot graph in which the TFs for \({}^{226}\)Ra, \({}^{238}\)U, and the stable elements (K, Mg, Fe, Al, Na, S, Ti, Ca, and Sr) are represented as variables. The range of transfer factors obtained for \({}^{238}\)U varied between 1.5\(\cdot\)10\({}^{-4}\) kg\({}^{-1}\) kg\({}^{-1}\) and 7.8\(\cdot\)10\({}^{-3}\) kg\({}^{-1}\) kg\({}^{-1}\), while for \({}^{226}\)Ra, the range was between 1.8\(\cdot\)10\({}^{-4}\) kg\({}^{-1}\) kg\({}^{-1}\) and 4.0\(\cdot\)10\({}^{-2}\) kg\({}^{-1}\) kg\({}^{-1}\). The ranges obtained for the transfer factors of \({}^{238}\)U and \({}^{226}\)Ra were similar to those observed in semi-arid climates [12; 18; 50; 51]. Furthermore, these transfer factors were also comparable to those found in mine tailings present in semi-arid climates [16]. Moreover, the transfer factors followed a logical pattern, with those obtained for \({}^{226}\)Ra being higher than those for \({}^{238}\)U [52]. The elements represented in the graph were those that exceeded the average contribution, as shown in the biplot graph of Figure 4. The KMO index was 0.54, which is low, but represents 57.3% of the variance and is higher than the value of 0.5 necessary to obtain statistically representative results [31]. The TFs obtained for \({}^{226}\)Ra and \({}^{238}\)U are consistent with those obtained by other authors in areas impacted and not impacted by U mining, which ranged between 2\(\cdot\)10\({}^{-4}\) and 0.1 kg kg\({}^{-1}\), whose characteristics are equivalent to those of the samples analyzed in this study [7; 8; 31; 53; 54]. Figure 5: A biplot graph showing the correlation between the concentration of \({}^{226}\)Ra (Bq kg\({}^{-1}\)) and \({}^{238}\)U (Bq kg\({}^{-1}\)) and the chemical composition, along with the scoring of the different soils studied based on these variables. The data used to construct this graph are found in Tables S1–S8 of the Supplementary Information. The biplot graph clearly shows four data sets directly related to the species studied (Figure 7). The species _Chenopodium vulvaria_ L. and _Chenopodium album_ L. are the ones least related to the radioactive content of the soils, as the angle formed by the variables \({}^{238}\)U and \({}^{226}\)Ra is 90\({}^{\circ}\), indicating no correlation. These plants are associated with the incorporation of K and Mg. K is often associated with a greater presence of mycorrhizal fungi, as confirmed by other authors such as [PERSON] et al. [55]. The presence of mycorrhizal fungi is, in turn, associated with less U absorption, as demonstrated in the previous studies [56]. Similarly, the incorporation of Mg is related to the reduced incorporation of \({}^{137}\)Cs and \({}^{226}\)Ra due to the competition of Mg for accessible positions in the soil [57]. The reduced incorporation of K and Mg by _Scolymus hispanicus_ L. and _Eryngium campestre_ L. imply a greater incorporation of \({}^{226}\)Ra mainly. On the other hand, the presence of Ti is related to the absorption of \({}^{226}\)Ra, as it favors its mobility; thus, increasing the incorporation of Ti would increase that of \({}^{226}\)Ra [58]. The results also show how the incorporation of \({}^{226}\)Ra is related to the incorporation of Ca and Sr due to their similar behaviors. However, as previously mentioned, Mg, although it is an alkaline earth metal, competes with these cations. Therefore, the incorporation of \({}^{226}\)Ra is coherent from the perspective of Mg, Ca, and Sr. Regarding U, the results showed that its content is greater in the case of _Scolymus hispanicus_ L. and this is associated with the incorporation of other heavy metals such as Fe and Al. The relationship between U, Fe, and Al was observed in the previous studies of granites [59], and it is consistent with the type of soil in the study area (see Section 2.1).