Toxic fluoride and carbonate bound fluoride in sediments from typical fluorosis areas.

Fluoride contamination in groundwater is a significant environmental issue globally, with serious implications for human health and agriculture (Ali et al., 2016). In the Yuncheng Basin of Shanxi Province, China, fluoride contamination has been a pressing concern due to the region’s high fluoride levels in both groundwater and sediments (Hao et al., 2023; Li et al., 2015). Understanding the mechanisms of fluoride mobilization and its association with sediment characteristics is crucial for developing effective mitigation strategies.

Fluoride, a naturally occurring element, can become problematic when it accumulates in high concentrations (Edmunds and Smedley, 2012; Jha et al., 2011). Its mobilization in sediments and groundwater is influenced by various geochemical processes. Recent studies have highlighted the role of sediment composition, mineralogy, and particle size in fluoride distribution and mobility (Gao et al., 2024). For instance, Wang et al., 2023a, Wang et al., 2023b demonstrated that fine sediment particles have a higher fluoride adsorption capacity due to their larger surface area and higher reactivity (Wang et al., 2023a). Similarly it is investigated the role of carbonate minerals in fluoride retention and release, noting that carbonate-bound fluoride can significantly impact groundwater quality (Du et al., 2022).

The Yuncheng Basin, known for its high fluoride concentrations, offers a unique opportunity to study fluoride behavior in sedimentary environments. Previous research has identified elevated fluoride levels in groundwater, with concentrations often exceeding recommended limits for drinking water (Chen et al., 2021). This study aims to further investigate the fluoride geochemistry of sediments in the basin, focusing on the forms of fluoride present, their association with sediment properties, and the influence of carbonate minerals.

Recent advances in analytical techniques have enabled more precise assessments of fluoride in sediments. Methods such as sequential extraction procedures and advanced spectroscopic techniques have improved our understanding of fluoride speciation and distribution. For instance, sequential extraction has been applied to identify various fluoride forms, including carbonate-bound and Fe-Al-bound fluoride, providing insights into their environmental behavior (Gao et al., 2024).

While previous studies by Zhang et al. (2022) and Wang et al., 2023a, Wang et al., 2023b from our laboratory have examined the hydrogeochemical mechanisms and microbial contributions to fluoride mobilization in groundwater of the Yuncheng Basin, these works did not explore the relationships between sediment grain size and specific fluoride fractions. This is the first comprehensive study to quantitatively assess the correlation between fluoride speciation in sediments and grain size distribution in the Yuncheng Basin. This novel approach helps to understand better the geochemical behavior of fluoride under varying sedimentological conditions.

This study builds upon existing knowledge by analyzing sediment samples from a borehole in Shandongzhuang Village, Qijizhen, within the Yuncheng Basin. We employ a combination of alkali fusion-ion selective electrode methods, particle size analysis, and X-ray fluorescence spectroscopy to characterize sediment fluoride content and its associations with sediment composition. By examining the correlation between fluoride content and particle size, as well as the role of carbonate minerals in fluoride mobilization, this research aims to contribute to a deeper understanding of fluoride dynamics in contaminated sedimentary environments (Fig. 1).