Fluorine Speciation in Loess in The Shaanxi Loess Plateau, Related Quality Assessment And Exposure Risks Implication

Abstract In this study, distributing characteristics of five fluorine (F) species in loess in the Shaanxi Loess Plateau (SLP) were determined including unextractable residual F (Fre), extractable water-soluble F (Fws), exchangeable F (Fex), F bound to Fe-Mn oxides (Ffm), and F bound to organics (For). The results show that unextractable Fre represents most percentage of Ftf in loess. Of the four extractable F species, the content of Fws is higher than the other three extractable F species in most loess samples. The loess in the southeast SLP has the highest Fws content while the loess in the southwest has the highest Ftf content. And the loess in the north SLP contains the lowest overall concentrations of Ftf and Fws. Similar to Fws, the respective content of Fex, Ffm, and For in the loess is also very low. However, the total of them and Fws cannot be negligible for F mobility in loess. Overall, the loess in the SLP can be assessed as inferior quality in terms of F as a result of high Fws content in most samples. Based on the F speciation in the loess, F exposure to grazing animals and humans, in fact to children, was assessed, indicating that F in the loess in the southwest SLP might pose a much greater risk to grazing animals than in other part of SLP as the loess contains more Ftf. However, there is no concern for the children’s exposure to loess F via ingestion in the study area in the present condition. As for the loess F risk to groundwater, it can be concluded that not only Fws but also the other extractable F including Fex, Ffm and For in loess may be responsible for the F enrichment in local groundwater in the area with the aid of the characteristics of F speciation in loess and distribution of local high-fluoride groundwater.