Geochemical Assessment of Heavy Metal Contamination in North Riyadh Soils: Pollution Indices and Multivariate Source Apportionment

Abstract

This study provides baseline information for environmental assessment in North Riyadh, Saudi Arabia. It assessed the concentrations of eight heavy metals, namely cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), nickel (Ni), lead (Pb), vanadium (V), and zinc (Zn), in 28 surface soil samples collected across the area. Pollution status was evaluated using the contamination factor (CF), geoaccumulation index (Igeo), enrichment factor (EF), pollution load index (PLI), and degree of contamination (DC), while Pearson correlation, principal component analysis (PCA), and standardized hierarchical cluster analysis (HCA) were applied to identify the possible sources of these metals. Iron was the most abundant element (mean 8482.14 mg kg−1), consistent with its role as a major crustal constituent. Co, Cr, Fe, Ni, and V showed low contamination (CF < 1) and a predominantly geogenic origin, reflected in strong inter-element correlations and a dominant rotated principal component explaining 54.8% of the total variance; Cu, Pb, and, in particular, Zn departed from this pattern, loading together on a distinct secondary component (32.1% of variance) and showing localized enrichment at a small number of sites. None of the 28 samples exceeded the pollution threshold for PLI (all < 1) or DC (all < 8), indicating that the soils of North Riyadh remain overall unpolluted with respect to these eight metals. These findings provide an early geochemical baseline for the district and identify Cu–Pb–Zn enrichment near construction and traffic corridors.