## 3 Results and Discussion
### Soil-to-Plant Transfer Factors for Trace Elements  
In order to better understand the role of soil and type of the contaminated area on the transfer of trace elements to these native plants, soil-to-plant transfer factor (TF) values for the 11 elements selected were calculated for each of the investigated plant species, as can be seen in Table 4. These TFs were determined using the average element concentrations found in plant species (Table 2) and soil samples (Table 3). \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline Species & Location & Cr & Mn & Ni & Cu & Zn & As & Cd & Pb & Sb & V & Co \\ \hline \multirow{3}{*}{_O. picensis_ (OP)} & **LM** & **1.671** & 0.113 & **2.165** & **1.091** & 0.488 & **1.354** & 0.219 & **3.571** & 0.433 & 0.121 & 0.195 \\  & **LG** & **1.371** & 0.360 & **2.394** & 0.582 & 0.492 & 0.245 & 0.177 & 0.285 & 0.264 & 0.078 & 0.233 \\  & **CH** & 0.032 & 0.058 & 0.109 & 0.259 & 0.230 & 0.031 & 0.047 & 0.056 & 0.092 & 0.019 & 0.027 \\ \hline \multirow{3}{*}{_S. velutina (SV)_} & LM & 0.939 & 0.088 & **1.381** & 0.762 & 0.555 & 0.825 & 0.237 & **1.329** & 0.216 & 0.037 & 0.097 \\  & CH & 0.763 & 0.069 & **1.225** & 0.284 & 0.231 & 0.026 & 0.191 & 0.055 & 0.101 & 0.008 & 0.036 \\ \hline \multirow{3}{*}{_A. subfusiformis (AS)_} & **LM** & 0.306 & 0.032 & 0.512 & 0.078 & 0.371 & 0.092 & 0.041 & 0.456 & 0.029 & 0.005 & 0.021 \\  & VA & **1.440** & 0.026 & **2.209** & 0.061 & 0.181 & 0.030 & 0.073 & 0.090 & 0.018 & 0.003 & 0.033 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Average transfer factor (TF) values of 11 TFs for the plant species collected at the different sampling locations. Los Maitenes (LM), La Greda (LG), Valle Alegre (VA), and yjr reference sampling point at Cachagua (CH). Underlined values indicate medium TF values (0.1–0.9), while those in bold indicate high TF values (>1). As it can be observed, TF values calculated for the different elements varied widely among the different plant species, ranging from 0.019 to 3.571 for _O. picensis_ (OP), 0.008 to 1.381 for _S. velutina_ (SV), and 0.003 to 2.209 for _A. subfusiformis_ (AS). In general, 44% of TF values were in the medium- and 40% in the low-level range for most of the assayed elements, indicating a low uptake by plants compared to the soil reservoir (Table 4). Based on the 11 elements investigated, Cr, Ni, Cu, As, and Pb had TF values > 1, which indicated enrichment of these elements in plants in some locations. Figure 3: TF values for the 11 trace elements (TEs) at each sampling location according to the plant species: (**A**) _O. picensis_, (**B**) _S. velutina_, and (**C**) _A. subfusiformis_. The red line indicates TF = 1, the low limit for element enrichment. Figure 3A shows a general tendency for the TF values for most of the trace elements: LM > LG > CH, except for Mn, Ni, and Co, where the higher TF values in LG were not related to higher concentrations in soil. Concentrations in soil of Cu, Zn, As, and V are above the guideline values for the world in at least one of the studied locations, as mentioned in Table 3 and by previous works in this area [10]. Regarding the present TF results, _O. picensis_ showed enrichment with Pb, Ni, Cr, As, and Cu (TFs > 1), as well as potential enrichment with Zn (TFs >0.5), so this species can be selected as a native plant for phytoremediation in highly polluted soils, especially in acidic soils with very low organic matter content, such as LM soils. Similarly, TF values obtained for the _S. velutina_ species were above 1 for Ni (1.381) and Pb (1.329) in LM and only for Ni (1.225) in CH. As Figure 3B shows, TFs for all of the trace elements in LM were higher than those obtained for the CH location, which is positively related to the closeness of LM to the industrial complex and the high soil element concentrations. Considering the present TF results, _S.