## 3 Results and Discussion
### Tungsten Uptake by Plants  
The concentration of tungsten in plants grown in the control soils (CT) was always under the limit of detection, thus the data are not reported. Considering the plants grown in the spiked soils, the uptake of tungsten was lowest in soil A and highest in soil C, with intermediate values in soil B. Data are reported in Table 3.  
Considering the mean of the five concentrations (from 10 to 100 mg kg\({}^{-1}\)), the tungsten concentration in the root portions increased with respect to soil A by an average factor of 2 in soil B and of 9 in soil C, respectively. A similar trend was found in the aerial part of the plants with an increase with respect to plants grown in soil A by an average factor of 3 and 15 in plants grown in soils B and C, respectively. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Shoot**} & \multicolumn{2}{c}{**Root**} \\ \cline{2-7}
**W in soil (mg kg\({}^{-1}\))** & **Soil A** & **Soil B** & **Soil C** & **Soil A** & **Soil B** & **Soil C** \\ \hline CT & 283 \(\pm\) 13.2a & 279 \(\pm\) 10.4a & 285 \(\pm\) 13.8a & 118 \(\pm\) 7.2a & 116 \(\pm\) 12.4a & 126 \(\pm\) 9.0a \\
10 & 281 \(\pm\) 14.6a & 275 \(\pm\) 14.7a & 295 \(\pm\) 19.3a & 115 \(\pm\) 9.1a & 114 \(\pm\) 10.1a & 124 \(\pm\) 8.3a \\
30 & 276 \(\pm\) 15.1a & 257 \(\pm\) 14.1a & 278 \(\pm\) 15.4a & 123 \(\pm\) 4.3a & 117 \(\pm\) 7.1a & 118 \(\pm\) 7.6a \\
40 & 263 \(\pm\) 11.2a & 263 \(\pm\) 12.9a & 251 \(\pm\) 16.1a & 129 \(\pm\) 8.6a & 121 \(\pm\) 8.6a & 122 \(\pm\) 8.1a \\
50 & 284 \(\pm\) 18.6a & 259 \(\pm\) 10.1a & 245 \(\pm\) 18.5a & 110 \(\pm\) 9.6a & 125 \(\pm\) 5.9a & 119 \(\pm\) 7.4a \\
100 & 251 \(\pm\) 16.3a & 269 \(\pm\) 16.5a & 269 \(\pm\) 13.6a & 119 \(\pm\) 5.1a & 116 \(\pm\) 4.9a & 115 \(\pm\) 5.9a \\ \hline \hline \end{tabular} Note: At each tungsten soil concentration, values with different letter in the same rows separately for shoots and roots are statistically different at \(p<0.05\).  
\end{table} 
Table 2: Biomass production (mg dry weight) of shoot and root grown in the soils with increasing tungsten concentrations. CT is the original soil. Values are the mean \(\pm\) standard deviation. The effects of tungsten on the physiological responses of plants were not studied, unless exclusively concerning the production of biomass. There are many studies that address these aspects to which refer for further deepening [30; 36]. Finally, we considered the dose-uptake relationship and the internal distribution of tungsten between the roots and shoots, which may have occurred within the time frame of this experiment. Table 3 clearly shows that the amount of tungsten in the plants differed significantly in the three soils at each tungsten concentration. Regardless of the type of soil, tungsten mainly accumulates in the roots, probably as a protective action, as tungsten does not play any essential role in the plant [37]. In fact, the translocation factor (TF), defined as the ratio between the tungsten concentration in the shoots and in roots, is always lower than 1 (Figure 1). Taken as the average at the different concentrations of tungsten in the soil, the TF values ranged from 0.19 (soil A) to 0.30 (soil C), with an intermediate value (0.25) in soil B. A different behavior of TF was observed between the three soils. It is worth noting that in soil C, as the concentration of tungsten increased, the TF decreased. Since, TF describes the passage of tungsten from the roots to the aerial part of the plants, the results obtained suggest that in the presence of high concentrations of tungsten in soils, the roots play a protective role acting as a filter and accumulating organ. These results are in agreement with those reported for _Raphanus sativus_ L. (radish) grown in an alkaline substrate [38]. Conversely, in soil A, as the concentration of tungsten increases, the TF increases. Soil B showed an intermediate trend; in fact, the TF increases up to a concentration of 40 mg kg\({}^{-1}\) of tungsten added to the soil, and then decreases.