Contamination and human health risk assessment of heavy metals in soil of a municipal solid waste dumpsite in Khamees-Mushait, Saudi Arabia

Abstract

The aim of this study was to evaluate the impact of heavy metal contamination from a municipal solid waste dumpsite on surface and deep soils as well as leaves of native plants in Khamees-Mushait city, Saudi Arabia. Heavy metal concentrations in surface and deep soil samples followed the order: Mn ≫ Zn > Cr > Pb > Ni ≈ Cu > Co while those in leaves samples followed the order Mn > Cu > Cr > Zn > Ni > Co > Pb > Cd, indicating different levels of metal uptake by plant. The r values of paired sample t-tests for the concentrations of each element in surface and deep soils indicate insignificant variation between heavy metal concentrations in surface and deep soil samples. Extreme correlation (r > 0.8) was observed for Co-Cr and Co-Pb, while no significant correlation was observed for Mn and Zn with other metals, suggesting different sources of Mn and Zn in the matrix of soil samples. Hierarchical cluster analysis showed no correlation between geographical locations and total heavy metal concentrations, indicating heterogeneous dumping of different domestic wastes in the site. The geochemical index and GIS mapping suggest extremely pollution by Co, Ni and Pb in the northwest of the study area and strong pollution by Cu, Cr, Mn and Zn in the southwest and northeast of the study area. However, the noncancer risk from all examined heavy metals through ingestion, inhalation and dermal exposure pathways for adults and children was insignificant. Furthermore, cancer risk from Co, Ni and Zn through inhalation exposure pathway was within the acceptable level while Cr reported unsafe cancer risk levels for both children and adults.