Spatial evolution analysis of groundwater chemistry, quality, and fluoride health risk in southern Hebei Plain, China

The present study investigated ion and fluoride concentrations in groundwater and their associated health risks to local populations in the southern Hebei Plain during 2018-2020. A total of 336 groundwater samples were collected from monitoring wells at 112 different locations. Statistical analysis, Gibbs diagram, principal ion ratio, and saturation index were carried out to clarify the chemical characteristics and control mechanism of groundwater. The results indicated that the groundwater types in the study area were mainly HCO₃-Ca, Cl-Na, and SO₄-Ca. The concentrations of cations and anions were Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ and HCO₃^- > SO₄^2- > Cl^- > NO₃^- > F^-, respectively. Based on the water chemical parameters, the pollution index of groundwater (PIG) was used to comprehensively evaluate the water quality. The results showed that during the study period, 60.41% of groundwater samples were suitable for drinking purposes, and 39.59% needed purification treatment to meet the requirements of drinking water standards. The groundwater quality in the western pre-hill plain areas was good, while the water quality in the northeastern and southeastern areas was poor and contaminated to varying degrees. Groundwater quality was mainly affected by the combined effect of total dissolved solids (TDS), Na⁺, Mg²⁺, Cl^-, SO₄^2- and HCO₃^- concentrations. Fluoride concentrations in the groundwater samples ranged from 0.07 to 8.51 mg/L, with 44% of the samples containing fluoride below the recommended limit of 0.5 mg/L, which would put the population at risk of dental caries. Also, 8% of the samples exceeded the permissible limit for fluoride in drinking water (1.5 mg/L), which would expose the local population to the risk of fluorosis. The human health risk evaluation of fluoride showed significant differences in non-carcinogenic effects between two different groups of children and adults. HI_in values ranged from 0.08 to 10.19 for children and 0.03 to 4.65 for adults, with hazard indices greater than 1 at 29.16% and 10.11%, respectively. This indicates that children have a greater exposure risk than adults, and the entropy of higher risk is mainly distributed in the northeast of the study area. Based on the above analysis of the spatial evolution of groundwater chemistry, water quality, and fluoride health risks in the southern Hebei Plain region, corresponding protection and management measures were proposed, which also provided reference significance for the effective use of drinking water and health risk prevention in the region.