Risk assessment of potentially toxic elements in groundwater using Monte Carlo simulation and geoaccumulation index near mechanical workshops premises, Omu-Aran

Abstract

Major activities in automobile workshops involve the release of toxic substances into the surrounding soil and water, which could pose adverse impact on human health. This study aimed at conducting a Monte Carlo simulation-based risk assessment for the concentrations of heavy metals (Lead (Pb), Iron (Fe), Chromium (Cr), Cadmium (Cd), and Arsenic (As)) and geoaccumulation index of these potentially toxic elements in the vicinity of mechanical workshops in Omu-Aran, Nigeria. Forty-eight samples were collected in hand-dug wells (HDWs) near automobile workshop premises and one control point in Omu-Aran. The water samples were subjected to acid digestion as a preparation step prior to evaluating their concentrations using an Atomic Absorption Spectrophotometer. The classification of contamination levels was determined using the geoaccumulation index (Igeo). Physicochemical and heavy metals parameters were determined in the groundwater samples using standard APHA methods. Data analyses were carried out by Monte Carlo Simulation and ANOVA at α0.05. All heavy metals (Pb, Fe, Cd, Cr, and As) were significantly different from control and above permissible limits. The detected heavy metal falls within categorized into three Igeo classifications, following Muller's interpretation: significantly to exceedingly contaminated (Cd), moderately to significantly contaminated (Pb, Cr, and As), and ranging from uncontaminated to moderately contaminated (Fe). Based on the result obtained from the Monte Carlo’s simulation, the observed hazard index (HI) values suggest that children have a higher likelihood (84%) of exceeding an HI value of 1 compared to adults (20%) when exposed to Cr in hand-dug wells (HDWs). In the case of Pb exposure via oral pathways, the computed lifetime carcinogenic risk (LTCR) values are comfortably below the 10−4 threshold, indicating no expected carcinogenic risk from Pb exposure. However, for Cr exposure in children through hand-dug wells (HWs), the LTCR values range from 0 to 2.14*10−4, signifying a potential risk associated with current Cr levels. The groundwater within the vicinity of auto mechanic repair activities areas in Omu-Aran has been greatly impacted negatively.