Contamination and risk levels of metals associated with urban street dust in Riyadh, Saudi Arabia

Urban street dust was collected from 22 locations in Riyadh, Saudi Arabia, and nine metals (Pb, Cr, Zn, Co, Cu, Al, Fe, Mn, and Ni) were investigated. The concentrations of these metals were employed in several common contamination evaluation indices to examine the contamination and the health risk caused by metals. Evaluation of these indices showed that they had variable degrees of contamination sensitivity. For individual contaminating elements (Pb, Cr, Zn, Co, Cu, and Ni), the sensitivities of the contamination of contamination factor (CF), the potential ecological risk (Ei), and geo-accumulation index (Igeo) were very similar. Therefore, these indices should yield very similar results. However, enrichment factor (EF) exhibited a different sensitivity pattern for determining the contamination caused by metals compared with the contamination level indicated by the other indices used in this study. Therefore, to avoid potential false indication of contamination, it is not recommended to use EF alone for determining contamination level. As indicated by four contamination evaluation indices (CF, Ei, Igeo, and EF), Riyadh was mainly contaminated by Pb. However, the health risk assessment results revealed that the Pb contamination level did not exceed the significant risk level for non-cancer effects. The cancer risk values indicated a negligible cancer risk to inhabitants of Riyadh exposed to metals associated with street dust. Considering the comprehensive contamination evaluation indices, the ecological risk index (RI) showed that about 77% of the sampling locations featured high ecological risk of which approximately 41% also featured high contamination indicated by pollution load index (PLI).