Hydrochemical Characteristics and Nitrate Health Risk Assessment in a Shallow Aquifer: Insights from a Typical Low-Mountainous Region

Wolong Town, Pingquan City, is located in a typical low-mountainous area of northern China, where groundwater is a crucial drinking water resource, thus, investigating groundwater’s hydrochemical characteristics and assessing nitrate-related health risks are vital for protecting, developing, and utilizing water resources. In this study, 66 groundwater samples were collected and analyzed for physicochemical parameters and major ion concentrations. Results showed that the groundwater in Wolong Town was weakly alkaline (average pH = 7.6), and classified as fresh water with TDS ranging from 90.0 to 900 mg/L. The dominant hydrochemical type was identified as HCO3−-Ca2+. Hydrochemical evolution was jointly regulated by natural water-rock interaction, anthropogenic nitrogen input, and environmental redox differentiation. Among these, water-rock interaction was the primary driver, where the hydrochemical composition was mainly shaped by the dissolution of halite, calcite, dolomite, and gypsum, coupled with cation exchange. Nitrate was the primary groundwater pollutant, with concentrations varying from 0.94 to 259 mg/L; elevation, soil type, and population density were key drivers influencing nitrate distribution. Health risk assessment indicated that nitrate posed significantly higher non-carcinogenic risks to infants and children than to adults, and long-term consumption of groundwater with excessive nitrate might induce adverse health effects. This study enhances understanding of shallow groundwater’s hydrochemical evolution and nitrate contamination-related health risks, thereby providing theoretical support for the sustainable development, utilization, and quality protection of groundwater resources in semi-arid low-mountainous areas.