[Characteristics of forms of fluorine in soils and influential factors]

Forms of fluorine in 15 different soils were studied using sequential chemical extraction procedure. The fluoride forms in soils were separated into five fractions: water soluble fluoride (Ws-F), exchangeable fluoride (Ex-F), fluoride bound to Fe/Mn oxides (Fe/Mn-F), bound to organic matter (Or-F), and residual fluoride (Residual-F). The contents of different fluoride forms were decreased in the order: Residual-F >> Ex-F > Ws-F > Or-F > AoFe-F. Correlation analyses showed that Ws-F was significantly correlated with Ex-F (r = 0.775* *). Ex-F was correlated with Fe/Mn-F (r = 0.5753*) and Organic-F (r = 0.5529*). Stepwise linear regression analysis was used to test the effect of various soil components on the contribution of fluoride forms, indicating that soil pH, organic matter, clay content, and exchangeable calcium content were the important influential factors and pH was the most important influential factor. In addition, soil parent materials had also influence on forms of fluorine.