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

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 (FH2O) and KCl solution (FKCl) ranged from 0.58 to 25.55 mg kg-1 and from 0.67 to 21.35 mg kg-1, respectively; hence, FH2O 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.