## 3 Results
### Resistivity of Cd in Cacao Farms  
After calibration, the 2D-ERT technique was useful in the field to analyze Cd in cacao subsoils. The tomography of farms in the Araucan municipalities showed the lowest resistivity range related to Cd (401-840 Ohm\(\cdot\)m) as shown in Figure 4A-C and Table 1, whereas higher resistivities were obtained at farms from Muzo and San Vicente de Chucuri municipalities (1616 and 1837 Ohm\(\cdot\)m, respectively), corresponding to 2.49 \(\pm\) 0.3 and 2.76 \(\pm\) 0.2 mg\(\cdot\)kg\({}^{-1}\) Cd, respectively, as shown in Table 1. The plots of 2D-ERT in farms from Muzo and San Vicente de Chucuri are shown in Figures 5B and 6C, respectively. Interestingly, except for Arauquita measurements, soil Cd levels higher than 1 \(\pm\) 0.4 mg\(\cdot\)kg\({}^{-1}\) also exceed 1000 Ohm\(\cdot\)m of resistivity values. At the Araucan farms (Figure 4A-C), the distribution of resistivity showed a tendency for a laminar formation, observed after the trial pit excavation. The resistivity values ranging from 401-840 Ohm\(\cdot\)m corresponds to highly saturated alluvial material when compared with other samples taken from the same location. The resistivity found at the sampled points did not show evidence of rock material content nor rock formation processes. Between 0.40-1.36 m soil depth, the deposition of clay material was observed with a resistivity ranging from 578-821 Ohm\(\cdot\)m related to semi-compacted clay. In the Tame municipality farms, a resistivity below 246 Ohm\(\cdot\)m was associated to the phreatic level observed in the assessed pits. Between 0.146-0.437 m depth, resistivity values ranging from 802-899 Ohm\(\cdot\)m (Figure 4C) were related to sandy-loam content. Regarding the Cd content in the municipalities, for instance in Arauquita, in the Ap boundary 1.16 mg\(\cdot\)kg\({}^{-1}\) was observed (see Table 1), whereas, in other soil depth, the Cd content was lower (ranging 0.03-0.07). In contrast, in farms from Muzo, between 5-15 cm depth, we found higher Cd content (ranging 2.01-2.49 mg\(\cdot\)kg\({}^{-1}\)). In farms from San Vicente, the higher Cd content was observed in boundary C, at 70 cm soil depth with 2.76 mg\(\cdot\)kg\({}^{-1}\), followed by boundary A in the first cm of soil depth (2.46 mg\(\cdot\)kg\({}^{-1}\)). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & **Arauquita** & & & **Muzo** & & **San Vicente** & \\ \hline
**Depth** & **Cd** & **Resistivity** & **pH** & **Cd** & **Resistivity** & **pH** & **Cd** & **Resistivity** & **pH** \\
**[cm]** & **[mg\(\cdot\)kg\({}^{-1}\)]** & **[Ohm\(\cdot\)m]** & **pH** & **[mg\(\cdot\)kg\({}^{-1}\)]** & **[Ohm\(\cdot\)m]** & **pH** & **[mg\(\cdot\)kg\({}^{-1}\)]** & **[Ohm\(\cdot\)m]** & **pH** \\ \hline
1 & 1.16 \(\pm\) 0.04 & 840.15 \(\pm\) 0.71 & 4.8 & 0.73 \(\pm\) 0.20 & 789.00 \(\pm\) 0.53 & 4.0 & 2.46 \(\pm\) 0.30 & 1616.00 \(\pm\) 0.95 & 4.9 \\
5 & 0.06 \(\pm\) 0.06 & 743.65 \(\pm\) 0.88 & 4.8 & 2.01 \(\pm\) 0.20 & 1305.00 \(\pm\) 0.47 & 4.2 & 1.13 \(\pm\) 0.20 & 1002.00 \(\pm\) 0.74 & 4.8 \\
15 & 0.04 \(\pm\) 0.03 & 620.11 \(\pm\) 0.46 & 5.1 & 2.49 \(\pm\) 0.30 & 1616.00 \(\pm\) 0.66 & 5.1 & 0.72 \(\pm\) 0.30 & 618.00 \(\pm\) 0.22 & 6.5 \\
30 & 0.07 \(\pm\) 0.07 & 574.53 \(\pm\) 0.53 & 5.6 & 0.50 \(\pm\) 0.50 & 556.00 \(\pm\) 0.89 & 5.6 & 0.97 \(\pm\) 0.40 & 617.00 \(\pm\) 0.49 & 6.8 \\
70 & 0.03 \(\pm\) 0.01 & 401.89 \(\pm\) 0.67 & 5.9 & 1.00 \(\pm\) 0.40 & 1300.00 \(\pm\) 0.97 & 5.5 & 2.76 \(\pm\) 0.20 & 1815.00 \(\pm\) 0.63 & 4.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Pseudo-total Cd content [mg\(\cdot\)kg\({}^{-1}\)], resistivity [Ohm\(\cdot\)m] and soil pH of composite soil samples collected per boundary of the pits dug in the municipalities of Arauquita, Muzo, and San Vicente de Chucuri. Data are shown as an average of the farms assessed per municipality. Both Cd and resistivity values are shown as mean \(\pm\) SD. At a farm in Muzo, the 2D-ERT shows a mixed deposition of parent material, SOM, and rock formations (Figure 5B).