Effect of Origin on Chemical Extractability of Fluorine in Soil and Its Consequence on Human Health Risk

Abstract

Exposure to fluorine (F) in soil increases the risks of dental and skeletal fluorosis and osteoporosis. Therefore, it is important to accurately determine the soil F concentration, and quantitatively evaluate the factors that affect the human health risk of soil F. Differences in soil F concentrations were investigated based on source type (anthropogenically contaminated or naturally enriched) and determination method (perchloric acid extraction-distillation (PAED) or alkali fusion-filtration). A soil sample without contamination history (background F concentration = 208 mg·kg⁻¹) was collected and injected with sodium fluoride (NaF) to prepare anthropogenically F-contaminated soil. Mica gravel (> 2 mm) was ground and mixed with quartz powder to mimic soil components of natural F origin. The F concentration in anthropogenically contaminated soil did not significantly differ between methods (slope = 0.959, p > 0.05). The concentration in the naturally F-enriched soil analyzed using alkali fusion-filtration was approximately twice that of the sample analyzed using PAED (slope = 0.548, p < 0.05). This significant difference was ascribed to the abundance of chemically stable F. Non-carcinogenic hazard quotients for children differed between methods in naturally F-enriched soil, at 1.335 (alkali fusion-filtration) and 0.641 (PAED). These findings offer valuable insights for assessing, managing, and remediating soils contaminated or enriched with F.