Fluoride is widely distributed in the natural environment and closely affects human health (Liu et al., 2021). In general, 80−90% of the fluoride in the human body is concentrated in the bones and teeth. Appropriate absorption of fluoride is beneficial to human growth and bone metabolism (Meng et al., 2021). However, excessive fluoride intake leads to dental fluorosis, skeletal fluorosis and other diseases, which seriously affects health (Yin et al., 2021). Numerous studies have shown that high fluoride concentrations in drinking water (> 1.0 mg L−1) can cause dental fluorosis and even bone fluorosis (Ahada et al., 2019; Narsimha et al., 2018).
Drinking water with a high fluoride concentration remains a challenge impacting the health of millions of people worldwide (Marghade et al., 2020; Narsimha et al., 2018). Drinking water fluorosis occurs widely worldwide and is prevalent to varying degrees in more than 50 countries and regions in Asia (India, Bangladesh, China, Thailand, Sri Lanka, etc.), Europe (Russia, Bulgaria, Italy, etc.), Africa, the Americas and Oceania (Zhang et al., 2016). China used to have one of the most serious epidemics of drinking-type fluorosis, with 1115 counties, 75,287 villages, and 72.07 million people affected (Zhang et al., 2020).
The Tibetan Plateau (TP) is one of the areas where both brick tea-type fluorosis and drinking-type fluorosis are prevalent (Lou et al., 2020). Researchers considered drinking brick tea to be the main cause of fluorosis in the TP because the average fluoride content of brick tea in this area is approximately 800 mg kg−1, which is far above the national safe threshold of brick tea fluoride concentration (300 mg kg−1) (Zhang et al., 2019; GB 19965, 2005). Therefore, previous studies on fluorosis in the TP were mainly focused on brick tea, ignoring the endemic of drinking-type fluorosis, which may mislead fluorosis prevention and treatment in the TP. In addition, it has been confirmed that compared with other fluorosis endemic areas, the same quantity of brick tea fluoride intake in the TP causes more severe fluorosis symptoms (Liu et al., 2020), which suggests that the superposition of fluoride intake via other pathways, such as through drinking water, makes fluorosis more serious. Unfortunately, to date, no data on the water fluoride concentration in the TP are available in the published literature.
The TP is the cradle of major Chinese river systems, including the Yellow River, Yangtze River, and Mekong River. Moreover, several important rivers in Southeast Asia, such as the Ganges, Indus, and Salween rivers, originate in this region. The TP is considered the “Asian Water Tower”, providing fresh water for nearly one-third of the world’s population (Qiao et al., 2021) and playing a vital role in maintaining human health and economic and social development. The water quality of the TP has a profound influence not only on China but also on all of southeast Asia. Therefore, it is of great significance to study the distribution and influencing factors of water fluoride in the TP.
Currently, the distribution of surface water fluoride is thought to relate to both natural and anthropological factors. Hydrochemical characteristics influenced by regional climate, topography and anthropogenic activities (Yin et al., 2021; Zhang et al., 2019; Liu et al., 2020; Ma et al., 2021). The temporal and spatial distribution of water resources and changes in water quality caused by climate conditions have generated a lot of research interest from scientists and governments in various countries (Zhang et al., 2021). However, most studies have focused on the impact of climate change on the amount of water, and relatively few studies have concentrated on changes in water quality (Ran et al., 2021; Duan et al., 2020). There is almost no discussion on the impact of climate change on fluoride distribution in water. Climate change affects the regional surface water cycle by changing the temporal and spatial distribution of meteorological factors such as air temperature and precipitation, influencing the migration and transformation of compounds and ions in the water (Gomiero et al. 2014; Rocha et al., 2015). Moreover, the change in topography in the plateau region leads to an uneven distribution of surface elements and makes the region prone to endemic diseases (Xu et al., 2018; Hettithanthri et al., 2021). Anthropogenic activities, such as effluent dischange, agriculture, will also influence hydrochemical characteristics (Kulk et al., 2021; Markogianni et al., 2016).
In this study, the fluoride concentrations in the surface water of major rivers and typical lakes in the TP were systematically analysed to clarify the spatial-temporal variation in fluoride and to estimate the health risks posed by surface water. Simultaneously, the possible anthropological activities, regional climate, and topography factors affecting the concentration and distribution of fluoride in the TP were discussed. This study is the first attempt to investigate the distribution characteristics, influencing factors, and human health risks of fluoride in the surface water over the TP, and it can provide a scientific basis for fluorosis prevention, water resource utilization, agricultural production, and animal husbandry in the plateau region.