Human health risk assessment of heavy metals in drinking water sources in three senatorial districts of Anambra State, Nigeria

Direct exposure to heavy metals (HMs) in drinking water beyond the allowable tolerable limit can adversely affect human health. The study evaluated the hazards (cancer and non-cancer) of HMs in drinking water for both children and adults based on hazard quotients (HQ) derived from the concentration of HMs in drinking water in Anambra State, Nigeria. Eighty-one water samples were collected from 5 water sources (borehole, well, sachet water, harvested rain, and stream water) in 3 districts of Anambra State, and their concentrations of selected HMs lead (Pb), cadmium (Cd), and mercury (Hg) were analyzed by Atomic Absorption Spectrometry (AAS). The health risks were assessed based on the concentrations of HMs in the water samples ingested orally. The concentrations of the HMs were higher than the permissible limits recommended by international agencies. The chronic daily intake (CDI) indices in the studied areas were highest for Cd. The CDI indices in the borehole, well, sachet water and, stream water samples were Cd>Hg>Pb for both populations. The CDI was higher in children compared to adults exposed to the same water sources. The hazard quotient (HQ) indices for HMs in the various water sources were in the order Cd>Pb>Hg for both populations. The hazard index (HI) of Pb was highest in rain water while that of Hg and Cd were highest in stream water for both adults and children. The incremental life cancer risk (ILCR) in the studied areas showed a higher risk for children than adults. Cadmium was a major risk factor and children at greater cancer risk than adults. Generally, the HQ and ILCR were greater than international standards with values for children higher than adults. The contribution of Cd towards HI and ILCR in all cases was significant. This study showed the concentrations of the HMs in drinking water sources, and their attendant HQ and ILCR. These values were higher than the permissible limits set by international agencies. The results demonstrated enormously worrisome risks for children than adults.