Bioaccessibility studies and human health risk assessment of potentially toxic elements in soils from Mechanic Workshops in Ogun State

Abstract

Soils in urban areas are usually contaminated by various potentially toxic elements (PTEs) which have potential impacts on human health and the environment. Some of the major activities that contribute to the pollution of soil are automobile repair workshops since the activities are often uncontrolled. This study examined PTE contamination in soils from automobile workshops in Ogun State, aiming to assess the concentrations, contamination factor, and human health risks of manganese (Mn) and cadmium (Cd) in soils from five mechanic workshops at Ijebu Ife, Ijebu Mushin, Ijebu Ode, Mowe and Sagamu. Samples were taken at the workshops from the upper soil layer of 0 to 10 cm. The samples were subjected to physicochemical characterisation and acid digestion and the PTEs were determined using AAS. Contamination factors, bioaccessibility, and risk assessment to human health were determined. Soil pH values varied between 8.1 to 9.0, which shows that the soils were alkaline. The mean total Mn concentrations were within the range of 42.0±1.3 - 64.8±1.5mg/kg and the Cd varied between 0.3±0.05 to 1.6±0.1mg/kg. The contamination factor value revealed a low degree of contamination of Mn and Cd in the locations. The mean bioaccessibility for Mn and Cd concentrations ranged from 19.30±0.03 to 64.40±0.1 mg/kg and 0.10±0.01 to 1.20±0.02 mg/kg respectively. Hazard quotient showed no significant concern for human exposure to the Mn and Cd in the soil via oral, dermal or inhalation pathways. In conclusion, Mn and Cd contamination was generally low in all the sites. However, this study recommends continued monitoring and implementation of environmental protection measures in such areas to prevent the accumulation of PTEs beyond tolerable contamination levels.