*3.4. Correlation Matrix*

Table 5 presents the correlation matrix among pseudo-total metals. In general, the correlations were in accordance with the results obtained by PCA.

Interestingly, all elements except Cd, Pb, Zn, and Hg were significantly (p < 0.01) correlated with Fe, a mostly lithogenic element. The correlation was negative for As and positive for the other elements.


**Table 3.** Total explained variance.

**Table 4.** Matrix of principal components analysis (significant loading factors are highlighted in bold).


Al metals associated in PC1 with positive loadings (Ti, V, and Fe) correlated positively with each other (p < 0.01). As and Hg correlated positively with each other (p < 0.05) and negatively with Fe, Ti, and V (p < 0.01), except Hg with Fe. Remarkably, the correlation between Ti and V was extremely high (r = 0.980, p = 0.0000).

The three elements combined in PC2 (Ni, Cr, and Co) correlated positively to each other (p < 0.01). Furthermore, the four elements combined in PC3 (Pb, Zn, Cd, and Cu) correlated positively to each other (p < 0.01).

**Table 5.** Spearman's correlation coefficient matrix between pseudo-total metal concentrations in the soils studied.


\* significant at p < 0.05 level; \*\* significant at p < 0.01 level.

## *3.5. Influence of Soil Depth and Gleyic Properties*

The concentrations of pseudo-total and bioavailable Cd and Zn, pseudo-total Cr and Ni, and bioavailable Cu were higher in surface horizons (Table 6).

The concentrations of pseudo-total Co, Cr, Fe, and Ni were higher in soils with gleyic properties than in soils without gleyic properties (Table 7). Furthermore, the concentrations of bioavailable Co, Ni, and Ti were higher in soils with gleyic properties than in soils without gleyic properties.

**Table 6.** Mean values and standard deviations of the concentrations (mg kg<sup>−</sup>1) of pseudo-total and Mehlich-3 extractable PTEs from surface (n = 35) and subsurface (n = 56) horizons of the urban soils studied and significance of equality of means (T-test). Significant differences (p ≤ 0.05) highlighted in bold.



**Table 7.** Mean values and standard deviations of the concentrations (mg kg<sup>−</sup>1) of pseudo-total and Mehlich-3 extractable PTEs of the urban soils studied, without gleyic properties (n = 62) and with gleyic properties (n = 29), and significance of equality of means (T-test). Significant differences (p ≤ 0.05) highlighted in bold.
