Hydrochemical insights into spatiotemporal characteristics of groundwater salinization and health risk assessment of fluoride in the south bank of Yellow River irrigation area, Northwest China.

The groundwater salinization problem in the south bank of the Yellow River irrigation area is severe, restricting the sustainability of groundwater resources. However, the groundwater salinization formation mechanism is unclear. Accordingly, this study analyzed the chemical characteristics and salinization mechanism of groundwater based on hydrochemical analyses (self-organizing maps, SOM), isotope analyses (δ¹⁸O and δD), and quantitative models (Rayleigh distillation model), as well as evaluating the potential health risks of fluoride. The results indicated that surface water and groundwater in the study area had high salinity and weak alkalinity, with the fluoride and total nitrogen (TN) content exceeding Grade III water standards. Additionally, only 42% of the water samples were suitable for drinking, with nitrogen sources being the main cause of water quality deterioration. Around half of the samples were unsuitable for irrigation. The spatial and temporal distribution of total dissolved solids (TDS) in the irrigation area was influenced by autumn irrigation. Overall, groundwater salinization was primarily attributed to evaporite dissolution, cation exchange, silicate weathering, and human inputs. Evaporation was not the main influencing factor. In addition, the non-carcinogenic risk of fluoride in the water body decreased as follows: infants > children > adult females > adult males. The results of this study deepen understanding of the relationship between changes in groundwater quality and the ecological environment in semi-arid inland areas, thereby promoting the rational utilization and scientific management of groundwater resources in the irrigation area.