# Temporal Variations of Heavy Metal Sources in Agricultural Soils in Malta
## 3 Results and Discussion
### Chemical Analysis  
#### 3.2.1 Descriptive Statistics  
The concentrations of the heavy metals studied listed in decreasing order are Fe > Zn > Mn > Sr > Pb > Cu > Ni > Cr > Co as shown in the descriptive statistics for the pre- and post-harvesting results in Table 5. The concentration results obtained indicate primarily that \begin{table}
\begin{tabular}{c c} \hline \hline
**Risk Factor Level** & **E\({}_{\text{i}}\) Value** \\ \hline Low potential ecological risk & E\({}_{\text{i}}\) < 40 \\ Moderate potential ecological risk & \(40\leq\text{E}_{\text{i}}\) < 80 \\ Considerable potential ecological risk & \(80\leq\text{E}_{\text{i}}\) < 160 \\ High potential ecological risk & \(160\leq\text{E}_{\text{i}}\) < 320 \\ Very high potential ecological risk & \(320\leq\text{E}_{\text{i}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Classification for the Potential Ecological Risk Factor (E\({}_{\text{i}}\)) [29]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Geo-Accumulation Index Level** & **Igeo Class** & **Igeo Value** \\ \hline Uncontaminated & 0 & Igeo \(\leq\) 0 \\ Uncontaminated/ moderately contaminated & 1 & 0 \(<\text{I}_{\text{geo}}\) < 1 \\ Moderately contaminated & 2 & 1 \(<\text{I}_{\text{geo}}\) < 2 \\ Moderately/strongly contaminated & 3 & 2 \(<\text{I}_{\text{geo}}\) < 3 \\ Strongly contaminated & 4 & 3 \(<\text{I}_{\text{geo}}\) < 4 \\ Strongly/extremely contaminated & 5 & 4 \(<\text{I}_{\text{geo}}\) < 5 \\ Extremely contaminated & 6 & 5 \(<\text{I}_{\text{geo}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Classification of geo-accumulation index (Igeo) [29]. the fields under study are not polluted by heavy metals since none of the concentrations quantified exceed reference limits set by legislation as documented in Table 6.  
With reference to Table 6, micronutrients Fe, Zn, and Mn presented higher concentrations in agricultural soil while Cr and Co had the lowest values, which results match findings from Spain and Iraq reported by [PERSON], et al., (2006) and [PERSON], et al., (2015) [4,33] respectively. Upon comparison of means for each element reviewed during the post-harvesting stage, it is observed that all concentrations have decreased considerably, except for Sr content which has slightly increased. This reduction in concentration may be attributed to several physical environmental changes such as the weather, water content variation due to differences in seasons, pH levels in the soil and crop uptake of the heavy metals analyzed which varies according to the macronutrient content and the time of crop harvesting [11,15,39]. The average heavy metals concentrations for all samples collected over both sampling stages do not exceed the reference values for Malta outlined in the 86/278/EEC Directive for agricultural soils except for Zn content which average exceeds the limit values marginally. Another study carried out by Briffa (2020) about agricultural soil in Malta used Dutch and Finland reference values for concentration limits [37]. The concentration results obtained in this study are within these limit values except for Zn content. Compared to other studies carried out in the Mediterranean region shown in Table 6, Zn content was higher but still within the legislation range outlined. The closest documented results (with an exception to Zn) are the ones reported by [PERSON], et al., (2014), which focused on soil from the Caia area in Portugal and Spain [35]. Further statistical analysis shall confirm whether the fields in