# Application of Biochar for the Restoration of Metal(loid)s Contaminated Soils
## 3 Results
### Effects of Biochar on Metal(Ioid)-Mobility  
High concentrations of metals are present in the contaminated soils compared to the uncontaminated soil tested (Table 1). The total concentration of metals present in the analysed soils does not vary significantly between the beginning and the end of the experiment, since it is a closed-box experiment carried out for a limited period. However, differences in the content of the different form of metal(Ioid)s analysed were observed between treatments. Distribution of the soluble and bioavailable forms of the metal(Ioid)s varied between RA and NC soils depending on the element studied. Thus, concentration of the soluble and bioavailable forms of As and Pb were lower in RA than in NC, unlike Zn and Cu which showed higher concentrations in RA, especially in the case of the soluble Zn (Table 2). In the amended soils, the soluble fraction of Zn significantly decreased with respect to the unamended contaminated soil, especially in the 8% treatment where it dropped up to 13-fold. The bioavailable fraction of Zn in the amended soils also decreased significantly with respect to the RA, dropping by half in RA8B, thus reducing its potential toxicity (Table 2). In both cases, however, soluble and bioavailable concentrations were higher \begin{table}
\begin{tabular}{c c c c} \hline  & **RA** & **RA4B** & **RASB** & **NC** \\ \hline
**Pb_s** (\(\mathrm{\SIUnitSymbolMicro kg}\)/kg) & 0.54 \(\pm\) 0.27 a & 0.88 \(\pm\) 0.62 a & 0.27 \(\pm\) 0.18 a & 16.53 \(\pm\) 3.84 b \\
**As_s** (\(\mathrm{\SIUnitSymbolMicro kg}\)/kg) & 4.83 \(\pm\) 0.29 a & 6.33 \(\pm\) 1.99 a & 5.57 \(\pm\) 2.76 a & 6.67 \(\pm\) 0.25 a \\
**Zn_s** (\(\mathrm{\SIUnitSymbolMicro mg}\)/kg) & 5.37 \(\pm\) 0.17 d & 3.39 \(\pm\) 0.06 c & 0.41 \(\pm\) 0.01 b & 0.02 \(\pm\) 0.01 a \\
**Cu_s** (\(\mathrm{\SIUnitSymbolMicro mg}\)/kg) & 0.33 \(\pm\) 0.02 c & 0.07 \(\pm\) 0.01 b & 0.02 \(\pm\) 0.01 a & 0.02 \(\pm\) 0.01 a \\ \hline
**Pb_b** (\(\mathrm{\SIUnitSymbolMicro kg}\)/kg) & 31.50 \(\pm\) 1.09 a & 40.50 \(\pm\) 2.35 b & 59.92 \(\pm\) 5.03 c & 6063 \(\pm\) 63.12 d \\
**As_b** (\(\mathrm{\SIUnitSymbolMicro mg}\)/kg) & 57.42 \(\pm\) 0.66 a & 56.92 \(\pm\) 1.30 a & 94.58 \(\pm\) 2.35 c & 84.17 \(\pm\) 0.78 b \\
**Zn_b** (\(\mathrm{\SIUnitSymbolMicro mg}\)/kg) & 8.97 \(\pm\) 0.40 d & 6.96 \(\pm\) 0.18 c & 4.19 \(\pm\) 0.06 b & 3.26 \(\pm\) 0.04 a \\
**Cu_b** (\(\mathrm{\SIUnitSymbolMicro mg}\)/kg) & 6.01 \(\pm\) 0.06 d & 5.27 \(\pm\) 0.05 b & 5.64 \(\pm\) 0.03 c & 2.64 \(\pm\) 0.03 a \\ \hline \end{tabular}
\end{table} 
Table 2: Soluble (_s) and bioavailable (_b) metal(Ioid) s content (mean \(\pm\) SE) in the non-contaminated soil (NC), in the unamended contaminated soil (RA) and in soil amended with biochar at 4% (RA4B) and 8% (RA8B) at the end of the experiment. Different letters indicate significant difference (\(p<\) 0.05) between treatments according to [PERSON]’s post-hoc test. Figure 2: pH and electrical conductivity (EC, \(\mathrm{\SIUnitSymbolMicro g}\)/m) of non-contaminated soil (NC) unamended contaminated soil (RA) and RA soil amended with biochar at 4% (RA4B) and 8% (RA8B) at the final time of the experiment. Error bars represent the standard deviation. Different letters for each parameter represent statistically significant differences (\(p<\) 0.05) according to [PERSON]’s post-hoc test. than in NC. In the case of Cu, its concentration decreased significantly both in the soluble fraction, where RA8B treatment reached similar values to the non-contaminated soil, and in the bioavailable fraction, although to a lesser extent since concentrations in RA8B treatment were higher than NC. In contrast, the soluble fraction of Pb showed no significant differences between amended and contaminated soil, while the bioavailable fraction increases with the percentage of amendment. However, the highest values of mobile forms of Pb were found in the non-contaminated soil. In the case of As, the soluble fraction did not show any significant difference between RA, RA4B, and RA8B (or with NC).