## 4 Results and Discussion
### Chemical Partitioning
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Trace Element** & \begin{tabular}{c} **F1** \\ **(Exchangeable +** \\ Acid Soluble)** \\ \end{tabular} & \begin{tabular}{c} **F2** \\ **(Reducible)** \\ \end{tabular} & \
\begin{tabular}{c} **F3** \\ **(Oxidizable)** \\ \end{tabular} &
\begin{tabular}{c} **F4** \\ **(Residual)** \\ \end{tabular} \\ \hline \hline \multicolumn{5}{c}{Amended soil (sample T10)} \\ \hline Cr & 0.096 \(\pm\) 0.012 & 0.201 \(\pm\) 0.011 & 4.80 \(\pm\) 0.16 & 20.4 \(\pm\) 1.77 \\ Ni & 2.79 \(\pm\) 0.29 & 17.7 \(\pm\) 1.16 & 9.64 \(\pm\) 0.99 & 14.2 \(\pm\) 0.4 \\ Cu & 23.2 \(\pm\) 2.2 & 554 \(\pm\) 24 & 282 \(\pm\) 22 & 398 \(\pm\) 12 \\ Zn & 116 \(\pm\) 17 & 436 \(\pm\) 46 & 158 \(\pm\) 9 & 203 \(\pm\) 17 \\ As & 0.545 \(\pm\)0.078 & 0.406 \(\pm\) 0.028 & 9.94 \(\pm\) 0.85 & 263 \(\pm\) 6 \\ Cd & 0.538 \(\pm\) 0.043 & 0.878 \(\pm\) 0.026 & 0.180 \(\pm\) 0.017 & 0.267 \(\pm\) 0.008 \\ Sb & 1.30 \(\pm\) 0.23 & 2.32 \(\pm\) 0.16 & 1.03 \(\pm\) 0.10 & 65.6 \(\pm\) 3.37 \\ Tl & 0.068 \(\pm\) 0.03 & 0.104 \(\pm\) 0.006 & 0.029 \(\pm\) 0.011 & 1.26 \(\pm\) 0.04 \\ Pb & 0.089 \(\pm\) 0.013 & 0.604 \(\pm\) 0.014 & 0.173 \(\pm\) 0.08 & 639 \(\pm\) 18 \\ \hline \hline \multicolumn{5}{c}{Control soil (sample ST10)} \\ \hline Cr & 0.375 \(\pm\) 0.010 & 9.7 \(\pm\) 0.77 & 6.65 \(\pm\) 0.53 & 38.6 \(\pm\) 5.52 \\ Ni & 2.43 \(\pm\) 0.19 & 1.20 \(\pm\) 0.13 & 0.848 \(\pm\) 0.082 & 12.4 \(\pm\) 2.1 \\ Cu & 149 \(\pm\) 4 & 182 \(\pm\) 13 & 95 \(\pm\) 9 & 335 \(\pm\) 43 \\ Zn & 35.6 \(\pm\) 1.1 & 14 \(\pm\) 1.0 & 8.39 \(\pm\) 0.8 & 96 \(\pm\) 15 \\ As & 0.671 \(\pm\) 0.056 & 139 \(\pm\) 10 & 3.19 \(\pm\) 0.32 & 553 \(\pm\) 69 \\ Cd & 0.095 \(\pm\) 0.007 & 0.089 \(\pm\) 0.010 & 0.030 \(\pm\) 0.003 & 0.283 \(\pm\) 0.037 \\ Sb & 0.423 \(\pm\) 0.067 & 14.2 \(\pm\) 0.16 & 1.33 \(\pm\) 0.12 & 185 \(\pm\) 11 \\ Tl & 0.026 \(\pm\) 0.003 & 0.105 \(\pm\) 0.011 & 0.039 \(\pm\) 0.003 & 2.20 \(\pm\) 0.05 \\ Pb & 0.047 \(\pm\) 0.004 & 52.2 \(\pm\) 3.6 & 0.284 \(\pm\) 0.055 & 1619 \(\pm\) 60 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Total trace element concentrations (in mg kg\({}^{-1}\)) analyzed by ICP-OES. The ability of PHE in the amended soil, expressed as the ratio between the most labile fraction (F1) and the sum of all other fractions (F2 + F3 + F4), decreased in the following order (values shown in brackets): Cd (0.41) > Zn (0.15) > Ni (0.07) > Cu, Sb (0.02) > As, Cr, Pb, Tl (<0.01). Accordingly, Cd is the most labile PHE in soil under the current conditions of the amended mini plot whereas mobility of the other PHE remains very low unless specific environmental conditions are induced in the soil system. Interestingly, the most labile PHE (Cd, Zn, Ni, and Cu) are those that have been concentrated in a greater proportion in the soil surface as a result of the MWS amendment. By comparing the fractionation pattern of PHE in topsoil, there are significant statistical differences between treated and untreated soil (Figure 7). The fraction of Cu, Zn, and Ni soluble in acetic acid (F1) was significantly lower in the amended soil than in the control soil (\(p<0.01\)). In contrast, the extractability of Cd, Sb, and Tl was significantly higher in the amended soil (\(p<0.01\)). The increased association of Cd with fraction F1 after soil amendment may suggest immobilization through carbonate precipitation by increased soil pH rather than sorption by cation exchange. It seems possible that adsorption could have been inhibited or limited due to the competition with Ca\({}^{2+}\) ions for binding sites [41]. Figure 7: Geochemical partitioning of trace elements in amended soil (sample T10) and control soil (sample ST10). Extraction yields are expressed as percentage of extracted trace elements in operationally defined soil chemical fractions: (F1) water soluble, exchangeable and weak acid soluble; (F2) reducible; (F3) oxidizable; and (F4) residual.