Human and ecological risk assessment, geo-accumulation, and source apportionment of road dust heavy metals in a semi-arid region of central Iran

This investigation aims to identify sources and assess the concentrations, spatial distribution patterns, and ecological and health risks of Zn, Pb, Cu, Ni, Cr, and Cd from road dust (RD) samples collected from Qom, Iran. Samples were collected from the surface of the roads, and were air-dried for 15 days. Debris including hair and leaves were removed from samples by using 1000-mu m nylon sieve. One gram of each dried samples were digested according to US environmental protection agency (USEPA) method using HCl, HNO3, and H2O2 for analysis of heavy metals (HMs), and utilising inductively coupled plasma optical emission spectrometry (ICP-OES). The mean concentrations for all HMs have higher values in the warm season with total mean concentrations of Zn = 227.3 > Pb = 130.1 > Ni = 94.2 > Cu = 78.7 > Cr = 39.5 > Cd = 2 mg/kg. Furthermore, correlations between all concentrations have been investigated using Pearson's method after approving normal distribution for all HMs through Kolmogorov-Smirnov (K-S) test. The spatial distribution of Pb, Zn, and Ni show higher concentrations in the periphery of Qom, while Cu, Cr, and Cd are almost the same for the whole city. The geo-accumulation index (I-geo) categorised all HMs as uncontaminated (average I-geo <0) except for Pb and Zn with average I-geo of 1.52 and 1.01, respectively. Ecological risk (E-r) analysis confirms lower risk for all HMs (average E-r <40). The warm season exhibits a higher potential ecological risk index (average RI = 81.73) for all components compared to the cold season (average RI = 75.85). Hazard index (HI), and carcinogenic risk assessment (CRA) values ranged lower than 1 and 10(-6), respectively, and thus, revealed negligible health risks for individuals. Positive matrix factorisation (PMF) points to four factors for HMs dominantly affected by traffic-related and anthropogenic activities (contributing 38.56%), and natural sources (accounting for 32.45%) in the cold and warm seasons, respectively.