# Temporal Variations of Heavy Metal Sources in Agricultural Soils in Malta
## 3 Results and Discussion
### Chemical Analysis
#### 3.2.3 Multivariate Statistical Analysis
Zn is the only element which for which a change in concentration between pre-harvesting and post-harvesting stage showed no particularly dominant link to its possible source. This is due to having high Zn concentration even available after growing crops. Such concentrations are probably affected by the accumulation of Zn content added anthropogenically over the years. Lithogenically, this owes its origin to the high natural Zn content in typical Mediterranean soils, while anthropogenic sources accounting for such accumulations including vehicle exhaust, combustion of fossil fuels, industrial emissions, and the leaching of wastewater [21; 36]. Concentration variations for Sr content are dominant and PC2 values for pre-harvesting and post-harvesting stages prove that its sources are of natural form. The negative correlations obtained with the Spearman's Rho and multivariate correlation analyses prove an inverse relation with the other elemental concentrations. Sr was attributed to the anthropogenic component in the work carried out by [PERSON], et al. (2020) [36], and to radioactive sources by [PERSON] (2018) [40]. As shown in the 3D scatter plots (Figure 2), Sr has a different coordinate loading from all other elements whose coordinates are closely grouped together. Sr is the most mobile element and since it can be present in a soluble or insoluble form, its uptake by plants during cultivation depends on its solubility state and thus its bioavailability [40]. Figure 2: 3D Scatterplot showing Principal 1, Principal 2, and Principal 3: (**a**) Pre-harvesting and Post-harvesting stages; (**b**) Pre-harvesting stage; (**c**) Post-harvesting stage. (Key: \(\times\) represents data from Field A pre-harvesting stage encircled in a black cluster; \(\bullet\) represents data from Field B pre-harvesting stage encircled in a black dashed cluster; \(\times\) represents data from Field A post-harvesting stage encircled in a red cluster; \(\bullet\) represents data from Field B post-harvesting stage encircled in a blue cluster. Co and Ni loadings in both the PCA and factor loading matrix show that their sources differed with fluctuating concentrations. Initial loadings and factor rotations demonstrate a dominant lithogenic origin at the pre-harvesting stage with loadings >0.8, although an anthropogenic origin is present. This confirms results documented by [PERSON], et al. (2006) and [PERSON], et al. (2020) but contrasts with those of [PERSON], et al. (2015) in the case of Co origins [4; 33; 36]. Loadings for Co and Ni with the post-harvesting stage analysis associate these elements to the anthropogenic source, although these are at a lower concentration. Such concentration variation in the results could have come about upon the combination with the surrounding activities in the vicinity of the fields, namely, from vehicular exhaust from neighbouring main roads, from the use of agricultural fertilizers which include natural manure for Field A and mineral fertilizer for Field B, from the leaching of wastewater which could possibly occur during precipitation seasons from neighbouring rabbit farms in the case of Field A, and from residues of fossil fuel combustion [18; 33; 35]. The latter source could be originating from an industrial zone in proximity of the fields, and from low flying aircraft at the airport which is close by. Increased activity during spring/summer months from such industry could possibly bring about such results. The overall analysis proves that Co and Ni content is not placing an anthropogenic negative effect on the soil because their effect was balanced out upon crop uptake.