Hydrochemical Characterisation, Heavy Metal Pollution, and Human Health Risk Assessment of Groundwater in Selected Coastal Communities of the Niger Delta, Nigeria

Groundwater is the primary source of domestic water supply in many coastal communities of the Niger Delta, Nigeria, despite increasing threats from heavy metal contamination associated with natural geological processes and anthropogenic activities. This study assessed the concentrations of heavy metals in groundwater and evaluated the associated human health risks in selected coastal communities of the Niger Delta. Twenty-four borehole water samples were collected and analysed for physicochemical parameters and heavy metals using standard analytical procedures. Heavy Metal Pollution Index (HPI), chronic daily intake (CDI), Hazard Quotient (HQ), Hazard Index (HI), lifetime carcinogenic risk (CR), Pearson correlation, and Principal Component Analysis (PCA) were employed to evaluate groundwater quality, identify contamination sources, and estimate potential health risks. Groundwater was slightly acidic to neutral, with pH values ranging from 5.72 ± 0.05 to 7.41 ± 0.03, while electrical conductivity and total dissolved solids ranged from 184.6–648.3 µS/cm and 118.2–412.5 mg/L, respectively. Iron exhibited the highest concentration (0.21–1.34 mg/L), whereas Pb, Cd, As, and Cr exceeded World Health Organization guideline values in several locations. HPI values ranged from 34.7 to 176.8, classifying 25.0%, 54.2%, and 20.8% of groundwater samples as low, moderate, and highly polluted, respectively. HI values ranged from 0.56–1.38 for adults and 1.12–2.63 for children, indicating greater non-carcinogenic health risks among children. The cumulative carcinogenic risk (3.8 × 10⁻⁵–1.6 × 10⁻⁴) exceeded the acceptable USEPA threshold in some locations. Correlation and PCA revealed that groundwater contamination originated from both geogenic processes and anthropogenic activities, including petroleum exploration, industrial discharges, artisanal refining, and improper waste disposal. The study demonstrates that heavy metal contamination poses significant public health concerns in the study area and recommends routine groundwater monitoring, pollution control measures, and appropriate treatment before domestic consumption.