Spatial distributions and probabilistic risk assessment of exposure to heavy metals in groundwater in a peri-urban settlement: case study of Atonsu-Kumasi, Ghana

Abstract

Heavy metal contamination has been of major concern at local, regional, and global scales due to its direct effect on human health. In this study, physico-chemical parameters and heavy metals (Cr, Cd, Fe, Zn, Pb, Cu, Zn and Mn) concentration in drinking water comprising of 12 mechanized boreholes (MBH) and 44 hand dug wells (HDW) in Atonsu, a suburb of Kumasi, Ghana were assessed. Carcinogenic and non-carcinogenic health risk assessments, sensitivity and uncertainty analysis for children and adults were carried out using Monte Carlo simulations technique. The results showed that, the chemical composition of the groundwater varies over a wide range both in salinity and ionic composition but lowly mineralized (TDS« 1000 mg/L). All the physic-chemical parameters were below their respective guideline values. However, about 21% of HDW had NO3− values above the guideline value of 50 mg/L. Co, Cr, Cu and Cd were below the detection limit of the instrument used for the analysis. Mn and Zn showed appreciable levels in some wells but below their respective guideline limits. However, 88.63% and 83.33% of the hand dug wells and boreholes had Pb above the guideline values. The non-carcinogenic hazard index (HI) for adult and children with respect to Fe and Mn were >1 signifying some level of risk. However, the carcinogenic HI with respect to Pb was <1. A sensitivity analysis for the oral and dermal exposure pathways for both adults and children indicated that the most important factors in the risk model are (1) the amount of the heavy metal consumed, (2) exposure duration and (3) ingestion rate. To protect public health, reduction of the metal's concentrations, proper construction of the wells to prevent runoff seepage and comprehensive water quality monitoring program are recommended to avoid/minimise the potential risk to the population.