Accumulation of Airborne Fluoride in Soils

Abstract Soil contamination by atmospheric fluorides was studied in the vicinity of an aluminum smelter. Soil profiles at various distances from the emission source were sampled and the samples analyzed for total and water‐extractable F. Both measurements, in particular the water‐extractable fraction, reflected the gradient of F exposure. The F concentration of the soil solution exhibited a similar dependence upon distance from the emission source. Over a distance of 8.8 km the total F concentration decreased from 2,700 to 616 µ g F g −1 , the water‐extractable fraction from 292 to 10 µ g F g −1 , and the F concentration in the soil solution from 8.2 to 0.3 µ g F mL −1 . Within an extensively sampled profile, the total F concentration was more‐or‐less constant, whereas the water‐extractable fraction increased significantly with depth. A soil column experiment was conducted in the field in order to estimate the rate of F accumulation and translocation. The F fluxes into and out of the main root zone were estimated to be in the order of 7.7 ± 3.5 and 5.4 ± 2.1 g F m −2 year −1 , respectively, which is roughly an equivalent of 5% of the F stored in a comparable uncontaminated profile.