## 3 Results
### Statistical Models (Polynomials Time Regression)

Table 2: Results of statistical analysis, for the interpolation (using first-degree polynomial) of lettuce mass variation over time, grown in soil with 4.5% zinc concentration. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Term** & **Coefficient** & **Std Error** & **95\% CI Low** & **95\% CI High** & **VIF** & **T** & **P** \\ \hline \(t^{0}\) & 1.656 & 1.218 & \(-1.153\) & 4.466 & NaN & 1.359 & 0.152 \\ \(t\) & 0.175 & 0.083 & \(-0.017\) & 0.368 & 14.5 & 2.106 & 0.053 \\ \(t^{2}\) & \(-0.0008428\) & 0.001168 & \(-0.003536\) & 0.00185 & 14.5 & \(-0.722\) & 0.291 \\ \hline \end{tabular}
\end{table} 
Table 3: Results of statistical analysis, for the interpolation (using second-degree polynomial) of lettuce diameter crowns variation over time, grown in soil with 4.5% zinc concentration. The interpolation curves corresponding to the polynomial Equation (2) are shown in Figure 5.  
Similarly, the polynomial regression expressions of time dependence were obtained for the other two soil contaminations, for the plant mass and their height, in accordance with the way lettuces have grown in the three types of soil. The graphical representations from Figure 6 demonstrate the regressions obtained. The three characteristics represented graphically have a generally monotonous tendency (within the entire 68-day monitoring period). Polynomial curves of a higher degree show that there are some points of local extreme, which could deviate from reality, which should be further researched from a biological or physical perspective. It can be observed that the linear interpolation confirms the inverse proportionality between the intensity of soil contamination and the increase of the plant's mass. The second-degree interpolation curves show that towards the end of the monitoring period, the three characteristics (mass, Zn concentration, and height) cease increasing or even have decreasing tendencies. This behavior is most likely generated by the polynomial function of the second degree. However, in the case of plant mass, both the third- and fourth-degree interpolation functions indicate decreasing tendencies at the end of the monitoring period, but only for the lowest soil \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Term** & **Coefficient** & **Std Error** & **95\% CI Low** & **95\% CI High** & **VIF** & **T** & **P** \\ \hline \(t^{0}\) & 0.59 & 1.309 & \(-\)2.506 & 3.685 & NaN & 0.45 & 0.343 \\ \(t\) & 0.424 & 0.176 & 0.008801 & 0.839 & 76.185 & 2.415 & 0.034 \\ \(t^{2}\) & \(-\)0.01 & 0.006169 & \(-\)0.025 & 0.004191 & 478.927 & \(-\)1.685 & 0.099 \\ \(t^{3}\) & 0.00009331 & 0.00005934 & \(-\)0.000047 & 0.0002336 & 200.478 & 1.573 & 0.115 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of statistical analysis, for the interpolation (using third-degree polynomial) of lettuce diameter crowns variation over time, grown in soil with 4.5% zinc concentration. Figure 5: Time dependence of the mass of lettuces grown in soil contaminated with 4.5% zinc concentration, for 1 to 4 degree polynomial interpolations. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Term** & **Coefficient** & **Std Error** & **95\% CI Low** & **95\% CI High** & **VIF** & **T** & **P** \\ \hline \(t^{0}\) & 0.142 & 1.427 & \(-\)3.35 & 3.634 & NaN & 0.099 & 0.381 \\ \(t\) & 0.657 & 0.321 & \(-\)0.129 & 1.444 & 246.875 & 2.044 & 0.06 \\ \(t^{2}\) & \(-\)0.028 & 0.021 & \(-\)0.079 & 0.023 & 5281 & \(-\)1.331 & 0.155 \\ \(t^{3}\) & 0.0005041 & 0.0004744 & \(-\)0.0006568 & 0.001665 & 12380 & 1.063 & 0.209 \\ \(t^{4}\) & \(-\)0.00003033 & 0.000003474 & \(-\)0.00001153 & 0.000005468 & 2948 & \(-\)0.873 & 0.252 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Results of statistical analysis, for the interpolation (using fourth-degree polynomial) of lettuce diameter crowns variation over time, grown in soil with 4.5% zinc concentration. contamination concentration (1.5%). In the other cases, the tendency is increasing, more or less convincingly, until the end of the monitoring period.