Spatial variation and fractionation of fluoride in tobacco-planted soils and leaf fluoride concentration in tobacco in Bijie City, Southwest China

Abstract

Fluorosis is a chronic systemic disease induced by excessive intake of fluoride (F⁻). Fluoride in water and foods has been widely concerned, while limited reports focused on F⁻ in soils and tobacco leaves which could transfer to human body. In the present study, we mainly focused on the distribution of F⁻ in tobacco-planted soils and tobacco leaves in Bijie City, Southwest China. Soil total F⁻ concentration ranged from 443.7 to 5,979 mg kg⁻¹. The level of F⁻ extracted by water (F_H2O) and KCl solution (F_KCl) ranged from 0.58 to 25.55 mg kg⁻¹ and from 0.67 to 21.35 mg kg⁻¹, respectively; hence, F_H2O could be used to indicate the bioavailability of soil F⁻ in the study area. The sequential extraction of F⁻ show that the residual and exchangeable F⁻ was the highest (97.44–99.73% of the total F⁻) and lowest (less than 0.25%) fractions of collected soil samples, respectively. According to the distribution of total and soluble F⁻ in the soil profiles at the depth of 0–100 cm, soils were polluted mainly at the 0–40 cm layer. The soluble F⁻ content in rhizosphere soils were higher than that in bulk soils, and tobacco leaves accumulated F⁻ ranged from 16.73 to 111.3 mg kg⁻¹ which was affected by soil pH and Ca content. Tobacco leaves F⁻ level was related to the maturity of the leaves, with the F⁻content of medium leaves being higher than that of top leaves. More attention should be paid to tobacco with high F⁻ content since F⁻ pollution may transfer to human body via tobacco smoking.