Heavy Metals and Microorganisms in Borehole Water Around the Olusosun Dumpsite in Lagos, Nigeria: Occurrence and Health Risk Assessment

Dumpsites are the most cost-effective and widely used method of waste disposal. However, studies have linked dumpsites to groundwater contamination, necessitating a safety assessment of groundwater sources near dumpsites. The safety of borehole water near the Olusosun dumpsite in Ojota, Lagos, Nigeria, was investigated in this study. Water samples were collected at distances of 100, 200, and 300 m from the dumpsite and subjected to conventional heavy metal analysis and microbiological tests. The average daily intake (ADI) and hazard quotient (HQ) of heavy metals were also estimated. The heavy metal analysis revealed that copper (Cu) and iron (Fe) levels exceeded permissible limits recommended by the World Health Organization (WHO) at the three locations, while manganese (Mn), lead (Pb), and cadmium (Cd) concentrations were within non-permissible levels only at the distances of 100 and 200 m. The concentrations of other heavy metals tested, such as zinc (Zn), nickel (Ni), and chromium (Cr), were within tolerable limits. The ADI of heavy metals at the three locations was within acceptable levels. However, the HQ of Cd in all the locations, as well as Pb at the distance of 100 m and Cr at distances of 100 and 200 m, was greater than the threshold of 1. The microbiological analysis revealed that all the water samples had non-permissible bacteria and coliform counts. The results obtained suggest that the borehole water around the dumpsite is grossly contaminated, with contamination levels increasing significantly (P ≤ 0.05) with closeness to the dumpsite (100 > 200 > 300 m). Therefore, there is a need for heavy metal remediation and disinfection of the dumpsite.