Ecological Risk Assessment and Pollution Models of Trace Metal Concentrations in Road Dust in parts of Enugu, Southeastern Nigeria

Abstract

Trace metal levels in road deposited sediments (RDS) from paved roads in Enugu metropolis, southeastern Nigeria were evaluated. The study aimed at determining the level of heavy metals in the RDS, with the objectives of identifying the sources of these pollutants in the environment.  Thirty-two (32) RDS samples from 10 selected major roads in Enugu were collected for this study. The concentration of Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb was analyzed using a flame atomic absorption spectrophotometer. The levels of physicochemical properties; pH, electrical conductivity (EC), total organic matter (TOM), and total organic carbon (TOC) was also established using standard procedures. The metal concentrations (mg/kg) were in the range; Cr (0.67 - 3.67), Mn (2.33 - 7.67), Fe (408.33 - 512.33), Co (3.00 - 61.75), Ni (39.67 - 193.67), Cu (11.50 - 90.00), Zn (1.00 - 31.67), Cd (0.00 - 1.33), and Pb (0.00 - 46.67). The pH, EC, TOC and TOM of the RDS samples range between 6.75-8.39, 556 - 578.67 μS/cm, 0.43 % - 3.49 % and 1.27 % - 10.35 % respectively. The relationships between the parameters were ascertained with correlation analysis. The likely source of these metals was recognized with principal component analysis and hierarchical cluster analysis, deployed to identify the potential source of these metals in the RDS. The results suggested that Mn concentrations did not exceed the crustal level. However, elevated Pb and Cd levels were recorded in the RDS samples. The models showed good consistency, indicating average to considerable levels of contamination of most parts of the studied major roads. PCA result revealed that metals in the RDS originated from three main sources which include the crustal, vehicular, and industrial sources.