Determining fluoride distribution and influencing factors in groundwater in Songyuan, Northeast China, using hydrochemical and isotopic methods

Abstract

Groundwater is the main source of drinking water for residents of the Songnen Plain, and its high fluoride content affects the health of residents. Previous studies have revealed hydro-geological conditions for fluoride enrichment, but relatively little research has been done on hydrogeochemical processes. In this study, the analysis of the stable isotopes and the water chemistry of 444 groundwater samples showed that high-fluoride groundwater has the characteristics of high Na+ and high HCO3−, and the pH is neutral to weakly alkaline. Geochemical analysis revealed that fluorite in the sedimentary layer is the main source of fluoride in the groundwater. In addition, the concentration of F− is related to the alkaline environment, human activity, fluorite solubility, cation exchange, and silicate weathering. The relationship between δ18O and F− indicates that evaporation does not have a notable effect on F− enrichment. Hydrogen and oxygen isotope analysis, combined with previous survey results on the groundwater circulation in Songyuan, show that the increase of the F− concentration in the Quaternary confined aquifer is either related to submerged overflow or to the destruction of the aquifer structure, due to artificial abstraction, indicating the effects of water cycle on the diffusion of F− between different aquifers.