## 3 Results and Discussions
### SEM-EDX Analysis Regarding Microstructure and Variability of Elements in Playground Soil  
The morpho-structure of soils picked-up from two different areas within a park (near and far from the play area) and different urban parks was analyzed by the SEM-EDX technique. Figure 4 highlights the SEM micrographs taken at 5000\(\times\) magnification, in five different sections randomly chosen in six samples from different locations. Generally, the fine powders show a compact surface with irregular shaped and different size particles, and low porosity.  
SEM images indicate the presence of both light and heavy elements in the studied soils, being recognizable through gray shades, from darkest to brightest. Therefore, different compounds, such as clay minerals, calcite, silica and many oxides, are highlighted by a specific geometry: spherical shaped and rod-like particles, well-defined edges or rounded flat microstructures. In addition, the semi-quantitative and qualitative EDX results support the imagistic results.  
By calculating the mean of the element percentages from five randomly scanned areas, we are estimating the elemental concentration and mineralogical diversity for each studied sample. Table 13 comprises data for 24 macro, micro and trace elements, with the atomic number ranging between C and Sr, which confirms the presence of minerals, organic matter and some heavy metals (Ni, Co, Hg, Pb, Sr, As) in the urban park soils.  
Figure 4: SEM imagistic results of soil samples collected from three areas in different city parks.  
Among the 24 identified elements, O (33.34 wt. % at 2 ES sample) and Si (14.63 wt. % at 3 PS sample) represent the major elements in all types of soil. The exception is carbon, whose values can be due on the one hand to the carbon tape used for soil fixation during analysis, and on the other hand to the presence of carbonate minerals (calcite--CaCO\({}_{3}\)) and CO\({}_{2}\) or the carbon footprint effect. Silicon is the most abundant microelement in the ecosystem [33]. Si-based compounds can be recognized from SEM images in both crystalline (as silicate matrices, clay and nonclay-like minerals) and amorphous phases. Other slightly inorganic elements are homogeneously distributed in all locations. Also, alkali metals are important in soil composition. K, Na, Mg and Ca are typically the higher accumulated elements in soil [84]. However, an alarming presence of toxic elements such as Hg (maximum of 3.52 wt. % at 10 PS sample), Pb (maximum of 3.39 wt. % at 10 PS sample) and Rb (maximum of 4.23 wt. % at 10 PS sample) in all the studied parks' soils was observed. The other important heavy metals are minors (below 1 wt. %). This fact could be explained by soil being positioned near industry areas and can be attributed to anthropogenic activities.  
Figure 5 shows the major and minor chemical element distribution maps in playgrounds' soils obtained through quantitative SEM-EDX analysis (Table 13, sample 2 ES). The EDX spectrum revealed the presence of the K-lines of C, N, O, Na, Mg, Al, Si, P, S, K, Ca, Ti, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb and Sr and the L-lines of Fe, Pb and Hg.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Average Concentration (wt. \%)**} \\ \cline{2-7}
**Element** & \multicolumn{2}{c}{**2**} & \multicolumn{2}{c}{**3**} & \multicolumn{2}{c}{**10**} \\  & **ES** & **PS** & **ES** & **PS** & **ES** & **PS** \\ \hline C & 19.57 & 25.28 & 25.30 & 46.83 & 33.19 & 34.76 \\ N & 1.21 & 1.25 & 1.24 & 1.91 & 0.82 & 1.44 \\ O & 27.01 & 29.90 & 31.52 & 26.2