# Temporal Variations of Heavy Metal Sources in Agricultural Soils in Malta
## 4 Conclusions  
The results obtained in this research increase the knowledge of heavy metals and their possible sources in Maltese agricultural soils. Physical studies have proven that the soil tested has a high organic content proving it healthy and abundant in natural nutrients making it adequate for crop cultivation. Concentrations obtained indicate that the fields under study are not polluted by heavy metals since none of the concentrations quantified exceed reference limits set by legislation. All elemental concentrations have decreased between the pre-harvesting and the post-harvesting sampling stages, proving the uptake of heavy metals by the growing crops from the soil matrix.  
The PCA carried out on the nine heavy metals reviewed at the pre-harvesting and post-harvesting stages, identified by two principal components, demonstrate the concentration dependency of all the elements to their possible sources affecting agricultural soils, except for Zn, whose concentration was marginally high even after harvesting the crops. The geo-accumulation index proved that the fields are moderately/strongly contaminated with Zn content.  
Results from the pre-harvesting stage indicate that Cr, Cu, Fe, Mn, and Pb are associated with anthropogenic sources available including the precipitation of pollutants in the rain from the atmosphere, fertilizer addition to prepare the soil for crop cultivation, urban dust, and vehicle and industrial emissions. Post-harvesting results for the same elements suggest a prevalent lithogenic source mixed with an anthropogenic one in the case of Cr, Fe, and Mn. Fe is only partially affected by the concentration available in the soil matrix due to the high natural Fe content typical of the soil. Results for Co and Ni reflect that, at the pre-harvesting stage, these elements were linked to a lithogenic origin, while at the post-harvesting stage their content was linked to an anthropogenic origin which could be originating from surrounding activities in the vicinity of the fields by neighboring industry, and other farming practices. Sr content, although concentration dependent, varies inversely to the other elements concentrations. Sr content remained relatively unchanged between the pre-harvesting and post-harvesting sampling stages hinting at natural sources.  
A health risk assessment study associated with the heavy metal content observed, showed that the concentrations available in both fields do not pose a carcinogenic risk or a hazard to human health upon ingestion or inhalation of the soil being studied during exposure. An assessment of the potential ecological risks associated with heavy metals content in the soil have demonstrated that the area studied is not contaminated by any of the metals except for Zn which creates a moderate to strong contamination but gives an overall low potential ecological risk.  
The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app12063120/s1](https://www.mdpi.com/article/10.3390/app12063120/s1)]([https://www.mdpi.com/article/10.3390/app12063120/s1](https://www.mdpi.com/article/10.3390/app12063120/s1)), Figure S1: Geographical information of the study areas and positioning of sampling points.  
Conceptualization, C.C. and F.L.; methodology, C.C. and F.L.; formal analysis, C.C. and F.L.; writing--original draft preparation, C.C. and F.L.; writing--review and editing, C.C. and F.L. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.