## 4 Discussion
### Correlations  
In order to show the relationships between metal concentrations and physicochemical parameters, a correlation matrix was performed on the obtained data set. Thus, high correlations (r = 1, or r > 1) indicate a perfect relationship or a very strong relationship between the variables, while \(p\) values assess the significance of the relationships between the values; a low \(p\) value indicates a statistically significant relationship between the variables, whereas a high \(p\) value suggests that the observed correlation could indicate an insignificant relationship [69]. In this study, the 0.1 probability level statistical test (\(p<0.1\)) was used to determine the degree of association between pairs of variables. The results between the assessed physicochemical parameters and heavy metals showed positive and negative and significant (\(p<0.1\)) and insignificant correlations (\(p>0.1\)) (Table 6). \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline  & **AI** & **MC** & **PV** & **RI** & **IV** & **SV** & **TPC** & **Mn** & **Cr** & **Cu** & **Cd** & **Pb** & **Co** & **Ni** \\ \hline
**AI** & 1.00 & \(-0.34\) & 0.25 & 0.26 & \(\mathbf{-0.65}\) & 0.16 & 0.36 & \(-0.27\) & \(-0.32\) & \(-0.22\) & \(-0.11\) & \(-0.13\) & \(-0.26\) & \(-0.32\) \\
**MC** & & 1.00 & \(-0.28\) & \(-0.34\) & 0.43 & 0.16 & \(-0.29\) & \(-0.40\) & 0.57 & 0.25 & 0.04 & \(-0.02\) & \(-0.44\) & 0.02 \\
**PV** & & & 1.00 & \(-0.15\) & \(-0.50\) & \(-0.25\) & 0.41 & \(\mathbf{0.63}\) & 0.04 & \(-0.25\) & \(-0.48\) & \(-0.31\) & 0.53 & \(-0.12\) \\
**RI** & & & & 1.00 & 0.36 & 0.52 & \(-0.05\) & 0.04 & \(-0.38\) & \(-0.22\) & 0.30 & \(-0.18\) & 0.03 & \(-0.61\) \\
**IV** & & & & & 1.00 & 0.22 & \(-0.56\) & \(-0.07\) & \(-0.05\) & \(-0.17\) & 0.36 & \(-0.05\) & \(-0.11\) & \(-0.05\) \\
**SV** & & & & & & 1.00 & 0.32 & \(-0.54\) & 0.39 & 0.11 & \(-0.24\) & 0.25 & \(-0.58\) & \(\mathbf{-0.66}\) \\
**TPC** & & & & & & & 1.00 & 0.03 & 0.27 & 0.08 & \(-0.18\) & \(\mathbf{-0.64}\) & \(-0.07\) & \(-0.51\) \\
**Mn** & & & & & & & & 1.00 & \(-0.15\) & 0.00 & 0.10 & \(-0.31\) & \(\mathbf{0.97}\) & 0.02 \\
**Cr** & & & & & & & & & 1.00 & \(\mathbf{0.72}\) & \(-0.40\) & 0.19 & \(-0.14\) & \(-0.18\) \\
**Cu** & & & & & & & & & 1.00 & 0.04 & 0.13 & 0.12 & \(-0.04\) \\
**Cd** & & & & & & & & & & 1.00 & 0.25 & 0.10 & \(-0.20\) \\
**Pb** & & & & & & & & & & & 1.00 & \(-0.38\) & \(-0.32\) \\
**Co** & & & & & & & & & & & & 1.00 & 0.13 \\ \hline \end{tabular}  
* The values in bold are significant (the \(p\)-value is below 0.1); r: perfect = 1, very strong = \(0.75\), strong = \(0.5\), moderate = 0.3, weak = 0.1. +: positive correlation, \(-:\) negative correlation. \(p\)-value \(<0.1\) significant, \(p\)-value \(>0.1\) insignificant.  
\end{table} 
Table 6: The pairwise Pearson correlation coefficients. For the physicochemical parameters, a strong, negative, and significant (\(p<0.1\)) correlation was observed between the acidity and iodine value \(r=0.65\), showing that, in most samples, acidity was observed to vary inversely regarding the iodine value. The significant correlation is given by the nature of free acids in the oil samples. Similarly, a strong but non-significant (\(p>0.1\)) negative correlation was observed between IV and PV (r = 0.50) and IV and TPC (r = 0.56), respectively, indicating that an increase in the value of one member of the pair (e.g., high unsaturated fatty acid content), will result in a decrease in the value of the other. On the other hand, a strong but insignificant positive correlation was observed between the RI and SV (\(r=0.52\)), the strong relationship being a measure of the fatty acid chain length. Regarding the relationship between the metals, a positive, significant correlation was observed between Co and Mn at a value of r = 0.97, showing the existence a similar origin in the soil matrix. The next significant correlation involves the Cu-Cr pair with r = 0.72; similarly, moderate correlations were observed between the Co-Pb and Cr-Cd pairs.