Source identification and health risk assessment of urban groundwater nitrate contamination in Chongqing, southwestern China

Chongqing, southwestern China Excessive nitrate (NO 3 ⁻) concentrations in groundwater pose considerable threats to human health. The identification of nitrate along with its transport mechanisms in groundwater systems and the associated human health risks is a critical challenge that requires urgent attention, particularly in urban areas. To reach the goals, 41 groundwater samples were collected from the urban area of Chongqing. Nitrate is the primary chemical parameter that exceeds regulatory standards (20 mg/L) in the groundwater of the study area, with an average concentration of 19.47 mg/L, and 20 % of the samples surpassing the threshold. The results of natural background levels and Moran’s index revealed that elevated NO 3 ⁻ concentrations were distributed within the Guanyinxia anticline, an area predominantly characterized by cropland. The Bayesian MixSIAR model indicated that agricultural activities were the primary contribution (27.7 % - 77.6 %) to the nitrate source in groundwater. In the Guanyinxia anticline, nitrate derived from agricultural activities accounts for more than 70 % of the total nitrate in groundwater. Hydrodynamic field simulations demonstrated that nitrate in groundwater predominantly migrated downward along the orientation of rock strata in the anticline. Human health risk assessment revealed that children may face non-carcinogenic risks due to nitrate exposure, with a maximum hazard index of 15.553. The non-parametric method further demonstrated minimal error in Monte Carlo simulations when applied to datasets containing outliers. These findings provide valuable insights into source identification and health risk assessment of urban groundwater nitrate contamination around the world. • NBLs and Moran’s index identified the anomalous nitrate concentrations. • More than 70 % of nitrate concentrations in hot spots originated from agricultural activities. • The nitrate in groundwater primarily transports downward along the orientation of rock strata. • Children are the most vulnerable population to the non-carcinogenic risks posed by nitrate. • Non-parametric Monte Carlo simulation produced a more accurate health risk assessment.