This paper is the result of groundwater contamination assessment.

Objective Groundwater serves as a crucial emergency water supply source in Xiamen City, Fujian Province. However, nitrate contamination has become increasingly severe due to industrialization and urbanization, posing threats to water supply safety and public health. This study aims to investigate the current status of groundwater nitrate contamination in Xiamen, assess its potential health risks to humans, and provide scientific evidence for groundwater pollution prevention and control. The findings will offer theoretical support for ensuring drinking water security and formulating effective groundwater management strategies.

Methods A total of 172 groundwater samples were collected from the study area. The nitrate contamination characteristics were analyzed using the single−factor pollution index method, and exposure risks for different populations (adult males, adult females, and children) were evaluated based on the non−carcinogenic human health risk assessment model established by the United States Environmental Protection Agency (USEPA).

Results The nitrate−nitrogen (NO₃⁻−N) exceedance rate in groundwater (based on the GB 5749—2022 standard limit of 10 mg/L) reached 49.4%, with 79.7% of groundwater samples contaminated by nitrate. Nitrate pollution was widespread across most of the study area. Domestic sewage from urban and rural areas was identified as the primary source of groundwater nitrate contamination. Compared to 1993, the average relative concentrations of NO₃⁻ and HCO₃⁻ in groundwater in 2019 increased by 17.5% and decreased by 15.3%, respectively. By 2019, the increase in NO₃⁻ relative concentrations significantly altered groundwater chemical composition, with 34.9% of samples classified as "nitrate−type water." Long−term exposure to high nitrate concentrations may pose non−carcinogenic health risks to 32.0% of adult males, 34.9% of adult females, and 55.2% of children.

Conclusions Groundwater nitrate contamination in Xiamen City is severe and poses a public health threat. It is recommended that the government strengthen sewage management and treatment in densely populated areas, mitigate anthropogenic impacts on groundwater, and ensure water supply safety.