Distribution characteristics and risk assessment of fluoride in surface water of urban typical rivers.

Fluoride is a common element in the Earth’s crust, widely distributed in the natural environment, and is also an important pollutant found in water resources (Qasemi et al., 2020; Ali et al., 2023; Qasemi et al., 2023). While a moderate intake of fluoride is beneficial to human health, excessive consumption can lead to adverse effects such as dental caries, dental fluorosis, and skeletal fluorosis (Li et al., 2017; Abiye et al., 2018; Li et al., 2019; Katiyar et al., 2020; Yin et al., 2021; Calero et al., 2022). Research indicates that the primary source of fluoride poisoning in humans is drinking water. The World Health Organization (WHO) recommends that fluoride concentrations in drinking water should not exceed 1.5 mg/L, while China sets a stricter limit of 1.0 mg/L (Narsimha and Rajitha, 2018; Ahada and Suthar, 2019; Yadav et al., 2019). Statistics reveal that fluoride overdose has affected >50 countries worldwide, with over 200 million people at risk. China is among the most severely impacted countries by drinking water fluorosis (He et al., 2020; Zhang et al., 2020; Mukherjee and Singh, 2022). Therefore, understanding the spatiotemporal variations of fluoride in water is crucial for addressing water quality issues.

Researches on fluoride pollution primarily focus on the distribution of high-fluoride groundwater, hydrochemical characteristics, and source analysis. Various factors, such as water temperature, pH, hardness, and the solubility of fluoride-containing minerals, can influence the fluoride content in water (Amouei et al., 2012; Ali et al., 2019; Yousefi et al., 2019b; Li et al., 2020a; Qasemi et al., 2020; Xiao et al., 2022). Hydrogeochemical processes, geological conditions, and rock weathering also influence fluoride enrichment (Dehbandi et al., 2018; Li et al., 2018; Kalpana et al., 2019). Studies in typical fluoride poisoning areas indicate that fluoride pollution poses greater risks to children than adults, potentially reducing children’s IQ by 16 % (Yu et al., 2018; Qasemi et al., 2020; Qasemi et al., 2023). Surveys show that groundwater in India, China, Kenya, Argentina, and Ethiopia frequently contains excessive fluoride levels (Ali et al., 2016; Zhang et al., 2017). Previous research on fluoride pollution has mainly focused on groundwater (Narsimha and Sudarshan, 2017; Huang et al., 2022; Tanwer et al., 2023). However, fluoride from surface water can also enter groundwater through hydrological cycles, posing risks to human health. Since the 1960s, China has undertaken efforts to improve water resources to reduce fluoride content but has rarely conducted systematic surveys on fluoride concentration in surface water or corresponding health risk assessments.

Rivers are crucial water resources for industry, agriculture, and daily life. They also serve as discharge sites for significant amounts of industrial wastewater, agricultural runoff, and domestic sewage. The quality and quantity of river water entering lakes directly influence the extent of lake pollution, acting as the primary driving force behind it. Chaohu Lake, one of China’s five major freshwater lakes, is located in Hefei, Anhui Province. The main surface water systems flowing through Hefei include the Nanfei River, Ershibu River, Pai River, and Shiwuli River. Among these, the main tributaries of the Nanfei River flowing through the urban area are the Sili River, Erli River, Banqiao River, and Shijia River. This study focuses on the Ershibu River, a significant tributary of the Nanfei River and an important component of the lake’s water system. Due to the discharge of industrial wastewater and agricultural runoff, the water quality of the Ershibu River is severely affected by fluoride pollution. However, there remains a lack of systematic understanding regarding the concentration distribution, influencing factors, and ecological and health risks of fluoride in the surface water of the Ershibu River.

Health risk assessment is a key topic in risk management strategies, with the calculation of the target hazard quotient (HQ) being the most common method. The HQ value quantifies the degree and likelihood of health hazards posed by harmful elements(Yousefi et al., 2019a). Additionally, Monte Carlo simulation is a crucial technique for assessing the probability of health risks from fluoride exposure, and its accuracy and reliability have been well established (Ali et al., 2021). This study focuses on the Ershibu River basin and aims to: (1) investigate the spatial and temporal variations in fluoride concentrations in surface water bodies within the basin; (2) identify the main sources of fluoride pollution in the water environment using a principal component analysis-multiple linear regression (PCA-MLR) model; and (3) evaluate the health risks associated with fluoride pollution by utilizing a health risk assessment model combined with Monte Carlo simulation. This study will provide a scientific basis for the management and control of fluoride pollution in this region.