Quantitative Assessment of Heavy Metal Contaminants and Associated Non-Carcinogenic Risks in Groundwater of Asaba Metropolis

Abstract

Groundwater continues to be a significant source of drinking water in the Asaba metropolis. However, its quality might be compromised given the increasing rate of urbanization and unsustainable anthropogenic activities. This paper therefore assesses the concentrations of selected heavy metals: Cu, Zn, Fe, Cr and Ni in borehole water from ten locations across the study area. In addition, it evaluates the non-carcinogenic health risks associated with exposure through consumption by adults. Water samples were collected using standard methods and analyzed according to the guidelines of APHA and WHO. ADI values as well as HQ were calculated using United States EPA risk assessment models, while overall exposure was evaluated as HI. The mean concentration of Cu (0.302 mg/l), Zn (0.431 mg/l) and Cr (0.032 mg/l) were all within the recommended threshold. However, Fe exceeded the WHO aesthetic threshold of 0.3 mg/L in most of the sampling locations with values reaching 0.73 mg/L. Nickel is the most critical parameter in this study, with concentrations ranging between 0.13 and 0.35 mg/l and exceeded the WHO health-based guideline of 0.07 mg/l in all sampling sites. Overall, risk assessment revealed that HI values in most of the locations were less than 1, suggesting low non-carcinogenic risk to adults under normal consumption patterns. However, about two sites (Site V and Site VII) have HI > 1, largely influenced by elevated Ni and Cr concentrations. Thus long-term consumption may pose health problems to some residents. These findings underscore the synergistic effect of geogenic and anthropogenic activities on the quality of groundwater in Asaba. Overall, this present study calls for improved standards in borehole construction and regular monitoring of groundwater resource as well as targeted environmental management interventional measures necessary to safeguard public health and sustainable access to wholesome drinking water supply within the metropolis.