Continental-scale distribution and source identification of fluorine geochemical provinces in drainage catchment sediment and alluvial soil of China

Endemic fluorosis is a worldwide health concern, which may be related to enhanced fluorine (F) in soil via food-to-mouth or respiratory system activity exposure to humans. Until now, continental scale data on F in the pedosphere is still deficient in China. In this paper, the distribution of enhanced F and the factors influencing this distribution are investigated using data of the China Geochemical Baseline project. The median values of F were 488 and 456 ppm in top and deep soil, respectively. In terms of spatial distribution, F in topsoil of China presents coastal and mountain low-value zones, central-south plain and southwest Karst high-value zones, and a northwest arid basin high-value zone. Thirty-three F geochemical provinces were delineated with F values of >700 ppm, which were predominately associated with geological background, intensive evaporation, and human activities. The formation of a high F anomaly area from the central–southern part to the southwestern part of China was related to the calcium-enriched soil and the superimposed coupling of multiple factors including the high F geological background, such as F-enriched organic matter strata, F-enriched phosphorus-bearing strata, F-enriched gypsum salt strata and mineralization processes. The high F anomaly area in northwestern China was not only related to the high geological background, but also associated with the secondary enrichment caused by evaporation.