Health Risk Assessment of Heavy Metal Pollution and Microbial Contamination of Borehole Water Sources in close proximity to Dumpsite in Kaduna, Nigeria

Abstract

Borehole water is widely used for drinking because it is generally considered a safe groundwater source; however, its quality may be compromised when boreholes are located near poorly managed waste disposal sites. This study assessed heavy metal contamination, bacteriological quality, bacterial diversity, antibiotic resistance, and associated health risks of borehole water collected near a military-operated dumpsite within the Nigerian Defence Academy (NDA), Kaduna, Nigeria. Fifty borehole water samples were analyzed for Cu, Zn, Co, Cr, Pb, Mn, Cd, and Ni using Flame Atomic Absorption Spectrophotometry. Microbiological quality was determined by Total bacterial and Coliform counts, while antibiotic susceptibility was evaluated using the Kirby–Bauer disk diffusion method following Clinical and Laboratory Standards Institute guidelines. Heavy metal concentrations were generally below guideline limits, although selected toxicants showed narrow safety margins. Maximum concentrations were Cu (0.1056 mg/L), Mn (0.0144 mg/L), Pb (0.0117 mg/L), and Cd (0.0030 mg/L), with cadmium reaching the World Health Organization and Nigerian drinking water limits. Noncarcinogenic risk assessment indicated a hazard index below 1, while chromium presented a low but non-zero lifetime cancer risk. Total bacterial counts ranged from 3.02 ± 0.08 to 4.89 ± 0.14 log₁₀ CFU/mL, and coliform counts from 1.02 ± 0.11 to 2.79 ± 0.09 log₁₀ CFU/mL. Predominant isolates included Staphylococcus aureus (80%), Escherichia coli (70%), Pseudomonas aeruginosa (60%), and Klebsiella pneumoniae (50%). Multidrug resistance was common, particularly among P. aeruginosa and E. coli. These findings highlight significant groundwater contamination and the need for improved waste management, routine monitoring, and water treatment before consumption.