Investigation Of Fluoride Source In Coal-burning Endemic Fluorosis Areas In Xinhua County

ObjectiveTo investigate the origin of fluoride in the coal-combustion endemic fluorosis areas in Xinhua County of Hunan Province; and to explore the pathway entering into the body, in order to provide scientific data for making preventive measures in the regions.MethodsFour primary schools (three fluorosis schools and one control school) were selected from Xinhua county of Hunan province. The prevalence of dental fluorosis of children aged 8-12 years in Grade 3~5 of every school was investigated. The villages in which the schools located were divided into three groups based on the prevalence of dental fluorosis. The samples of household around the schools in three groups were collected, including drinking water, indoor and outdoor air, coal, briquettes(the mixure of coal and binder clay), briquette ash, binder clay, fresh chillies and rice grown in the local soils, farming soils(soils in vegetable fields and paddy fields). The F content in these samples was determined by fluoride ion selective electrode method, in accordance with the Chinese National or Professional Standards. The volatile quantity of fluoride per kilogram briquette was calculated. Chi square test was performed to test??ther there was significant difference in the prevalence of dental fluorosis among groups. ANOVA of complete randomized design was applied to analyze the difference in F content of all samples among three groups. The correlativity of F content among different samples was analyzed by Pearson correlation.ResultsThe significant difference was found in the prevalence of children`s dental fluorosis among three groups (P<0.001). The F concentration of water in three groups ranged from 0.05mg/L to 0.18 mg/L, which was under the national standard. The F concentration of indoor air in fluorosis areas was higher than that in non-fluorosis area but the difference was not statistically significant (P>0.05). The volatile quantity of fluorine per kilogram briquette showed significant difference (P<0.05) and it was higher in fluorosis areas than that in control area (P<0.05 ), there was no statistical difference between two fluorosis groups (P>0.05). A positive correlation was observed between the volatile quantity of fluorine per kilogram briquette and the F concentration of indoor air (r=0.648, P<0.01).The F content of coal in three groups ranged from 31.29 to 122.15 mg/kg. The F content in coal and briquette ash showed no statistical difference among groups (P>0.05). The F levels of briquettes, binder clay showed significant difference (P<0.01) and it was higher in fluorosis areas than that in control area (P<0.01), there was no statistical difference between two fluorosis groups (P>0.05). The fluoride content in the briquettes correlated with that in binder clay(r=0.627, P<0.01). The volatile quantity of fluorine per kilogram briquette and the fluoride content in indoor air were positively correlated with the fluoride content in the briquettes, with r=0.742, 0.508 respectively.The F content in fresh food(chillies, rice) had statistically significant difference among three groups(P<0.01), it was higher in fluorosis areas than that in control area (P<0.01) and there was no statistical difference between two fluorosis groups (P>0.05).The F content of farming soils showed significant difference (P<0.01), and it was higher in fluorosis ar??than that in control area (P<0.01), there was no statistical difference between two fluorosis groups(P>0.05). There was significant correlation between the F content of soils in vegetable fields and that in chillies(P<0.01), the F content of soils in paddy fields and that in rice had good linear relationship (P<0.05).Conclusion1 The F content in binder clay is high but that in coal is not. The main fluoride source polluting indoor air resulting from coal combustion is binder clay in Xinhua County fluorosis areas.2 The F content of fresh foodstuff (chillies, rice) is higher than in control area in Xinhua County. It is one of the important pathway by which the fluoride entered into body. Fluorine in farming soils is an important source of the F content in foodstuff.