# Temporal Variations of Heavy Metal Sources in Agricultural Soils in Malta
## 3 Results and Discussion
### Chemical Analysis
#### 3.2.1 Descriptive Statistics
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{3}{*}{**Element**} & **Mean** & **Study From** & **Study from** & **Study from** & **Portugal-** & **Study from** & **Concentration** & **Target** \\  & **Concentra-** & **Spain by** & **Iraq by** & **Greece by** & **Spain** & **Egypt by** & **target** & **Values for** \\  & **tions in This** & **[PERSON], et al.** & **[PERSON], et al.** & **[PERSON], et al.** & **Border by** & **[PERSON],** & **Values for** & **Malta by** \\  & **Study** & **(2006)** & **(2015)** & **(2010)** & **[PERSON], et al.** & **et al.** (2020)** & **Soil (ppm)** & **86/278/EEC** \\  & **(mg/g)** & **(mg/kg)** [4]** & **(mg/kg)** [33]** & **(mg/kg)** [34]** & **(pmpm)** [36]** & **(pm)** [37]** & **(mg/kg)** [38]** \\ \hline Co & 0.100 & 7 & 3.430 & 8.300 & - & 31 & 20 & - \\ Cr & 0.339 & 27 & 11.590 & - & 0.850 & 128 & 100 & - \\ Cu & 0.818 & 23 & 2.010 & - & 1.230 & 61.800 & 36 & 100 \\ Fe & 2594.401 & 13,608 & 235.770 & - & - & 62,583 & - & - \\ Mn & 41.898 & 295 & - & - & - & 1099 & 200 & - \\ Ni & 0.461 & 21 & 8.960 & 9.430 & 1.950 & 70.600 & 35 & 70 \\ Pb & 3.034 & 23 & 3.820 & 161.360 & 3.160 & 30.700 & 85 & 100 \\ Sr & 9.969 & - & - & - & - & 308 & - & - \\ Zn & 207.262 & 53 & 5.500 & 3.520 & 0.640 & 143 & 50 & 200 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Heavy metals contents in Mediterranean soils. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{3}{*}{**Variable**} & **Symbol** & \multirow{3}{*}{**Unit**} & \multicolumn{4}{c}{**Descriptive Statistics**} \\ \cline{3-6}  & & & **Pre-Harvesting** & **Post-Harvesting** & **Mean** & **Standard** \\  & & & **Concentrations** & **Concentrations** & **Mean** & **Deviation** \\ \hline Cobalt & Co & HB/g & 0.150 & 0.047 & 0.100 & 0.055 \\ Chromium & Cr & HB/g & 0.450 & 0.197 & 0.339 & 0.214 \\ Copper & Cu & HB/g & 1.456 & 0.108 & 0.818 & 1.092 \\ Iron & Fe & HB/g & 3814.549 & 729.829 & 2594.401 & 1290.501 \\ Manganese & Mn & HB/g & 66.338 & 15.118 & 41.898 & 27.021 \\ Nickel & Ni & HB/g & 0.824 & 0.0915 & 0.461 & 0.370 \\ Lead & Pb & HB/g & 4.373 & 1.331 & 3.034 & 4.026 \\ Strontium & Sr & HB/g & 10.050 & 10.197 & 9.969 & 1.236 \\ Zinc & Zn & HB/g & 254.888 & 157.437 & 207.262 & 59.237 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Descriptive statistics of heavy metal contents in soil in \(\mu\)g/g—Pre-harvesting and Post-harvesting stages. this study are in fact polluted with high Zn content and aid in outlining possible Zn sources to remediate and reduce such contamination. The only study that determined Sr content is by [PERSON], et al., (2020) but the values documented by this work are by far higher than found in this study [36]. No limit reference values were found for Sr content in agricultural soil. The distributions at the pre-harvesting stage of Co and Ni are symmetrical since the skewness coefficient is close to zero. The other distributions are asymmetrical since a discrepancy between the mean and median values could be observed, and high values for the skewness coefficients resulted. From the post-harvesting stage analysis, the distributions of Sr and to a certain extent of Zn for Field A resulted symmetrical proving homogenous distributions. Cr is the only elemental distribution that is symmetrical and thus homogenous over Field B in both sampling stages. Non-point sources could be attributed to the origin of these homogenous distributions, such as air pollution effects from vehicle, aircraft emissions, industrial emissions, and urban dust. [PERSON], et al., (2010) suggested that Co and Ni are derived from the parent material since their highest concentrations were recorded at a lower sampling depth (<25 cm) and both metals are usually rich in soil with high organic matter [34]. The other distributions for Fe, Zn, Mn, Sr, Pb, Cu, and Cr could be linked to the dumping of waste or inorganic material, falling hunting shots, and the use of paint and oil on site.