Dynamic analysis of groundwater chemistry from 1997 to 2018 in the eastern part of Yongning County, Ningxia Hui Autonomous Region of northwestern China: Integration of Bayesian water quality assessment and health risk assessment.

Groundwater is an important part of water resources, with many characteristics: widespreading, steady changing, good water quality, and usable. Therefore, it is an ideal drinking water source. However, with the rapidly economic development and the accelerated urbanization process, the problem of groundwater pollution has become increasingly serious. In this study, the eastern part of Yongning County was taken as the study area, 30 groundwater samples from 1997 to 1998, 2007 to 2008, and 2017 to 2018 were selected for water quality assessment and health risk assessment. The results showed that the groundwater chemical type had a tendency to change from HCO₃-Ca·Mg type to SO₄·Cl-Ca·Mg type, and the rock weathering was the important factor controlling the groundwater hydrochemistry in the eastern part of Yongning County. The water quality evaluation of Mn and As was grade II, and the water quality evaluation of Cu, Zn, Cr⁶⁺, Cd, and Mo was grade I. Both carcinogenic and non-carcinogenic risks were higher in children than in adults, the acceptable frequency of adults was higher than that of children, and the area with higher risks was distributed in the central and easternmost regions of Yongning County. As was a more sensitive factor to carcinogenic risk than Cr⁶⁺. Therefore, we should pay more attention to the governance of As and the health of children's drinking water. Special attention also should be paid to the water environment protection in the eastern parts of Yongning County. Water quality assessment and health risk assessment in the study area lay a foundation for water pollution control and water environmental protection in the future. PRACTITIONER POINTS: The hydrochemical type changes from HCO₃-Ca·Mg type to SO₄·Cl-Ca·Mg type, which is mainly affected by rock weathering. According to the Bayesian water quality assessment: Mn and As was II, and Cr belongs to I is small. As was the main carcinogenic factor, Mn was the main non-carcinogenic factor, and the risk was higher in children than adults.