Investigation of Fluoride Source in Coal-burning Endemic Fluorosis Areas in Hunan Province

Objective To explore the origin of fluoride in the coal-combustion endemic fluorosis areas in the middle part of Hunan Province and to provide basic data for making preventive measure in the regions. Methods In November, 2006, the prevalence rate of dental fluorosis of children aged 10-12 years were examined, the villages were divided into three groups based on the prevalence rate of dental fluorosis. The fluoride content in the drinking water, coal, briquettes, briquette ash, clay and indoor air was determined by fluoride ion selective electrode. The quantity of fluoride release was calculated. Results There was no significant difference in the concentration of fluoride in water among the three groups, and it was below 1.0 mg/L in fluorosis and non-fluorosis areas. The fluoride levels in the coal, briquette ash and indoor air showed no statistical difference among groups. The fluoride levels of briquettes, clay and the quantity of fluorine release showed significant difference (P0.01, P0.05, P0.05) and it was higher in fluorosis areas than that in control area(P0.05 or P0.01). The fluoride content in the briquettes was positively correlated with that in clay (r=0.561, P0.05). Conclusion As the coal combustion, the fluoride source is mainly from the clay used as the binder and selecting low fluoride content clay as the binder should be taken as the important measure to prevent fluorosis in the middle part of Hunan province.