## 3 Results and Discussion
### PCA and Soil Spectral Characteristics  
Using PCA, two principal components were extracted (Table 3), together explaining approximatively 86% (PC1: 71.23%; PC2: 14.95%) of the information contained in the initial variables. The distribution of variables in the plane defined by these two components (Figure 2) shows that much of the variables contribute strongly to the first PC; only one variable (Tri-CB) contributes significantly and positively to the second PC. PCBs18, Hepta-CB, Hexa-CB, and EOX are positively correlated among them, and negatively correlated with Tetra-CB and Penta-CB, as found in a previous work [26]. Using PCA and CA, soil samples were classified into three groups (Figure 3), separated one from the other along the first principal axis. Group C1 was characterised by the highest values of Tetra-CB and Penta-CB, while group C3 was characterized by: (i) the highest content of PCB congeners with high numbers of chlorine atoms in the biphenyl molecule (Hexa- and Hepta-CB), (ii) the highest concentration of total PCBs (PCBs18), and (iii) the highest content of extractable organic halogens (EOX); group C2 had intermediate chemical characteristics between those of groups 1 and 3. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Statistics**} & \multirow{2}{*}{**EOX**} & \multirow{2}{*}{**PCBs18**} & \multirow{2}{*}{**Tri-CB**} & \multicolumn{2}{c}{**Tetra-**} & \multirow{2}{*}{**Penta-CB**} & \multirow{2}{*}{**Hexa-**} & \multirow{2}{*}{**CB**} \\  & & & & & & & & \\ \cline{2-7} Min & 0.1 & 0.1 & 0.0 & 0.3 & 15.5 & 26.0 & 0.6 \\ Max & 5000.0 & 16,991.3 & 8.2 & 34.9 & 64.7 & 48.2 & 38.0 \\ Mean & 622.2 & 2350.2 & 2.0 & 6.3 & 32.8 & 40.3 & 18.6 \\ CV \% & 213.9 & 207.2 & 130.2 & 125.4 & 40.5 & 14.3 & 70.5 \\ Skewness & 2.2 & 2.2 & 1.5 & 2.1 & 0.4 & \(-\)0.6 & 0.2 \\ \hline \hline EOX = extractable organic halogens; PCBs18 = sum of the 12 polychlorinated biphenyls dioxin-like and 6 indicators-polychlorinated biphenyls, Tri-CB, Tetra-CB, Penta-CB, Hexa-CB, Hepta-CB = percent of tri-, tetra-, penta-, hexa-, and hepta-chlorobiphenyls in the PCBs18. & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Descriptive statistics of EOX and PCB contents in the soil samples. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **PC1** & **PC2** & **PC3** & **PC4** & **PC5** & **PC6** & **PC7** \\ \hline Eigenvalue & 4.99 & 1.05 & 0.58 & 0.22 & 0.14 & 0.03 & 0.01 \\ Variability (\%) & 71.23 & 14.95 & 8.21 & 3.11 & 2.06 & 0.37 & 0.06 \\ Cumulative (\%) & 71.23 & 86.18 & 94.39 & 97.51 & 99.57 & 99.94 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Principal component analysis of EOX and PCB contents. Mean reflectance spectra of soils from each of the three groups (Figure 4) show some evident differences in the overall reflectance (albedo), the convexity of the spectra, and the slopes in different spectral regions. Figure 3: Scatterplot of the soil samples on the plane of the first two principal components resulting from the application of PCA to EOX and PCB contents. C1, C2, and C3 identify the three groups of soil samples resulting from the application of the Cluster analysis to the scores of the first two main components. Figure 2: Contribution of EOX and PCBs to the first two principal components resulting from the application of PCA to the same parameters. Differences in the overall reflectance are noticeable in the NIR, between 800 and 2450 nm. In particular, as the concentration of total PCBs (PCBs18) and related variables (Hexa-CB, Hepta-CB, and EOX) increases, the overall reflectance in this region decreases. The influence of PCBs8 on the spectra slopes in the visible and first part of the NIR regions also appears evident (Figure 4). Specifically, as the PCBs8 contents increases, the slope in the green (550-600 nm), red (600-800 nm), and NIR (800-1100 nm) ranges decreases distinctly.