Contamination and Hazard Risk Assessment of Potentially Toxic Elements in Road Dust Lagos, Southwest, Nigeria

Abstract

The purpose of this study was to determine the concentration, sources of pollution and health risks associated with 16 potentially toxic elements (PTEs) in 120 urban road dust samples in the city environ of Lagos, southwest, Nigeria. For all road dust samples, Zn, Se, Mo, Ag, Cd and Pb were higher than background values as defined by Upper Continental Crust (UCC) values, whilst 50, 96, 3, 20, 20, 5 and 5% of the samples showed higher values for U, Cu, V, As, Cr, Ti and Fe, respectively. The spatial distribution maps showed that pollution hotspots for Pb, Zn, Cu, Cr, Se, Ag, Cd and Mo were concentrated in densely populated areas with a high volume of traffic and industrial areas such Ikeja, Ojo, Alimosho and Kosofe regions. Ninety five percent of the samples provided a Pollution Load Index (PLI) greater than 1, indicating the presence of pollution inputs. The calculated Contamination Degree (CD) was between 10 -174 for PTE's with an average of 58, exhibiting a moderate to very high degree of contamination. The potential ecological risk index (RI) ranged from 39 -3496, with a mean value of 678 where 7% of the samples provided a low ecological risk index, 5% a moderate risk, 34% and 38% a considerable and very high ecological risk. The non-carcinogenic health risk index showed that Mo, Pb and Co accounted for 87% of the Heath risk index value for both children and adults with a low to moderate exposure risk following the order: dermal > ingestion > inhalation. The carcinogenic risk showed that Ni posed no carcinogenic risk in the dust, Co and As were within low risk, Pb and Cd posed a low and moderate carcinogenic risk to both children and adults in the study area. Road dusts from industrial and densely populated residential areas with high traffic influx exhibited a higher pollution and health risk index compared to less densely populated residential areas in Lagos. This confirmed vehicular traffic as the main source of the PTEs in the dust samples of the study area.