Impact of microbial activity on fluoride release from sediments in areas with high fluoride groundwater: Mechanisms, sources and the lithology diversity.

This study explores the interplay between microbial activity and sediment lithology in influencing fluoride release from sediments. Sediment samples, collected from Yuncheng Basin: a region known for significant groundwater fluoride contamination, exhibit fluoride concentrations well above the global average, ranging from 206.2 mg/kg to 780.9 mg/kg. These samples comprising silt, silt loam, and sandy loam, are enriched with minerals such as quartz, calcite, albite, chlorite, and illite. Microbial batch incubation reveals that microbial activity significantly enhances fluoride release, particularly in silt loam sediments. The results from sequential extraction first timely identified that the carbonate-bound and Fe-Al-bound fluoride fractions are the most affected forms of fluoride by microbial activity, highlighting the roles of mineral dissolution and desorption in fluoride mobilization. Further batch incubation experiments demonstrate significant increases in fluoride concentrations, especially in silt loam sediments, indicating the role of microbial processes in accelerating fluoride release. Additionally, the study unveils diverse patterns of dissolved elemental concentrations during incubation, with varying release patterns for calcium, magnesium, iron, aluminum, and manganese. These findings illustrate the complex biogeochemical interactions that govern fluoride mobilization in these sediments. Sequential extraction studies further elucidate the intricate mechanisms of fluoride release, with microbial activity primarily influencing the release of carbonate-bound and Fe-Al-bound fluoride. This study also sheds light on the co-dissolution of fluoride and calcium, offering valuable insights into geochemical processes driven by microbial interactions within the sediment matrix.