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. The level of F extracted by water (F) and KCl solution (F) ranged from 0.58 to 25.55 mg kg and from 0.67 to 21.35 mg kg, respectively; hence, F 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 which was affected by soil pH and Ca content. Tobacco leaves F level was related to the maturity of the leaves, with the Fcontent 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.