Assessment of Deep Groundwater Quality and Associated Human Health Risks in the Heilonggang Basin, North China

Anomalous enrichment of geogenic fluoride and iodine in groundwater has become a major geogenic environmental concern in the Heilonggang Basin of the eastern North China Plain. In this study, 353 deep groundwater samples were collected to assess groundwater quality and human exposure risks. Piper diagrams, inverse distance weighting interpolation, the entropy-weighted water quality index (EWQI), the US Environmental Protection Agency human health risk assessment (HHRA) framework, and Monte Carlo simulation (MCS) were integrated to evaluate the health risks associated with F^- and I^- exposure. Groundwater pH ranged from 6.40 to 8.99, and the groundwater was generally weakly alkaline. Na-Cl was the dominant hydrochemical facies. I^- concentrations ranged from below the detection limit to 0.96 mg/L, while F^- concentrations ranged from 0.42 to 8.14 mg/L. Both constituents were markedly enriched in the eastern coastal area of Cangzhou. The EWQI assessment indicated that only 47.8% of the samples were classified as having excellent or good water quality. Poorer groundwater quality was mainly observed in the eastern coastal zone. The estimated health risk from drinking-water ingestion was substantially higher than that from dermal contact. For fluoride exposure, the mean hazard index (HI) exceeded the acceptable threshold for adults, children, and infants across the study area. Monte Carlo sensitivity analysis further showed that exposure concentration was the primary determinant of health risk, accounting for 68.7%-68.9% of the total variance. Infants and young children were particularly susceptible to exposure. These findings demonstrate that deep groundwater in the eastern Heilonggang Basin poses potential health risks due to elevated fluoride and iodide levels. The results provide a scientific basis for groundwater management and for preventing endemic diseases in comparable groundwater systems across the North China Plain.