Spatial Variability and Health Implications of Heavy Metals in Wadi Al-Hamd’s Groundwater: A Multivariate and Risk-Based Approach

This study comprehensively evaluates heavy metal (HM) contamination and associated health risks in 31 groundwater samples from Wadi Al-Hamd, northwest Saudi Arabia. Cd, Pb, Zn, As, Cr, Cu, Ba, and Ni showed variable concentrations, some elements approaching WHO guideline values in localized samples. The analyzed HMs showed variable concentrations, with As reaching 5.02 µg/L (50% of WHO guideline) in sample M27. The heavy metal pollution index (HPI) ranged from 0.15 (M29) to 10.07 (M27), with values below 15 indicating low pollution overall, while the metal index (MI) ranged from 0.022 (M29) to 0.621 (M27), all below the threshold of 1 for safe water, indicating geogenic enrichment, particularly in arsenic and nickel. Principal component analysis identified three PCs explaining 73.58% of total variance, with PC1 (35.50%) dominated by Zn-Cu-Ni (geogenic weathering) and PC2 (23.62%) by As-Cd (redox-driven dissolution). Health risk assessment via chronic daily intake (CDI), hazard quotient (HQ), and hazard index (HI) models confirmed negligible non-carcinogenic risks (HI < 1) for both adults and children, though children exhibited 1.5–2 times higher exposure. The highest HQ values were observed for As (HQoral-child: 0.365 in M27), approaching but not exceeding safety thresholds. Dermal exposure contributed minimally (<1% of total risk). The average lifetime carcinogenic risk (LCR) due to exposure to arsenic through drinking water aligns with the US EPA’s acceptable risk range of 1 × 10−6 to 1 × 10−4 (average 1.18 × 10−5 for adults, 2.06 × 10−5 for children). These findings align with regional studies, but highlight localized As high values for few samples. The study underscores the dominance of natural weathering in HM release and provides a framework for targeted groundwater management in arid regions.