Human and ecological risk assessment of heavy metals in different particle sizes of road dust in Muscat, Oman

Heavy metal contamination of Hg, As, Cu, Cr, Zn, and Pb was investigated in three different fractions 45, 125, and 200 μm of road dust in Muscat, Oman. Dust samples were collected from three different traffic roads, viz. high, medium, and low based on traffic volume and then sieved individually before they analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES). Cu has the highest level among the analyzed metals while the lowest amount was for Hg. Most of the metals in all traffic sites have higher concentration in finer fraction and the concentrations of Cu, Pb, and Zn in HT road dust decreased significantly from finer fraction (45 μm) to bigger fraction size (200 μm). The risks of analyzed heavy metals to the urban ecosystem and human health were calculated by the potential ecological risk index and human exposure model, respectively. Risk index levels of studied metals in the three fractions and roads vary from strong to very strong potential. Hg found to have the greatest contribution in risk index in the three different fractions and roads. The values of risk levels for individual metal contamination in the dust street samples from different roads and fractions were ranked in the following order: Hg > Cu > Pb > Cr > Zn. Ingestion is the main pathway of exposure to road dust particles for both children and adults, followed by dermal contact absorption. The HI for children and adults exposed to 45- and 125-μm particles were higher than exposed to 200-μm particles, which indicated that finer particles tend to have higher non-carcinogenic risk. The non-carcinogenic risks of the studied heavy metals to children and adults are within safe threshold value; however, health risks of Cr, Pb, and Cu were relatively high for children.