Evaluating the pollution footprint of traffic-derived trace elements in roadside soil and the associated risks in a non-metropolitan city

Abstract

This study evaluated the influence of multiple traffic-related conditions, including proximity to a road, car parking, highway, road junction, and transport stop, commonly observed yet largely overlooked in many non-metropolitan cities of developing nations, on trace element (TE) contamination in roadside soil and the associated risks in a secondary South African city. Among the evaluated TEs (As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sb, Zn), mean Cu and Pb concentrations exceeded national soil quality guidelines at 100% and 86% of sites, respectively, whereas pollution assessment revealed generally moderate Sb, Pb, Cr, Ni, Co, Mn, and Zn contamination at > 71% of sites; indicating 73% of TEs as potential environmental threats. Of the seven examined localities, a mean pollution load index above 1 suggested soil pollution at a site affected by most traffic conditions. Regression analysis indicated positive relationships between road proximity and concentrations of all TEs, with significant (p < 0.05) associations for 75% of the identified contaminants, along with As and Ba. Significant positive correlations between TEs exhibiting higher contamination suggested shared sources. This was further supported by principal component analysis, which associated 73% of TEs with one or more traffic variables, primarily road proximity, transport stop, and highway, and secondarily car parking. Moreover, origin from multiple traffic sources was suggested for most TEs. Nearly moderate ecological risks for Cd and Pb at two sampling points, and potential cancer risks for children from As, require follow-up investigation. The findings provide valuable insights into the globally underexamined pollution footprint of multiple traffic-related factors and highlight the need for their management to promote ecosystem sustainability in comparable cities.