The Use Of Benchmark Dose Method In Health Risk Assessment Of Children In Florosis Area After Water Supply Improvement

Fluorine is one of the elements which is widely distributed and closely related with human health, it has double effects to human health. Insufficient or exceed intake can all have adverse effect to human health. If the intake of fluorine is insufficient or exceed, the prevalence of dental caries will all increase; If the intake is exceed for a long time, it cause the endemic fluorosis of which main features is dental fluorosis and skeletal fluorosis.Health risk assessment is base on some principles, it overall evaluate the adverse effect of human health affect by environmental harmful factors. The classical health risk assessment includes four steps: hazards identification, dose-response assessment, exposure assessment, risk characterization.Now more and more researchers tend to use benchmark dose(BMD)method to make reference dose(RfD). Compared with traditional no observed adverse effect level(NOAEL)method, BMD method has the following advantages:①overall assesses the dose-response curve, not like NOAEL method only focus on one dose;②use confidence interval to evaluate and consider variation factors;③base on benchmark response(BMR) to chose,acknowledge the BMD related response level, BMR can be set up by researchers;④BMD method provide a more credible method, avoid the incidence of extreme events caused by NOAEL. This research used BMD method in health risk assessment of children in fluorosis areas after water supply improvement.Objective: Use the BMD method in health risk assessment of children in fluorosis areas after water supply improvement, analyze the relationship between urine fluoride and each indicators of biological effects, calculate the BMD of each indicators of biological effects and find the sensitive indicators of surveillance, forecast the health level of children in fluorosis areas after water supply improvement..Method: Base on the time of water supply improvement and water fluoride, we selected four villages from fluorosis area(village A,B,C,D) and one control village(village E) of which residents have the same living habits with the four villages. We adopted the introduction of Ion selective electrode method to determine the content of fluoride in drinking water and urine, record the time of water supply improvement of each village, examine the prevelacne of dental fluorosis and caries. We random selected 100 students(half male half female) in each village and determine their AKP,BGP,CT in serum and bone mineral density. We make urine fluoride as exposure indicator, use BMD method to calculate the BMD and BMDL of fluoride exposure to each indicator of health effects. We use health risk assessment of children in fluorosis areas after water supply improvement, assess the health level of children in fluorosis areas after water supply improvement.Results: Before water supply improvement, fluoride in drinking water of four fluorosis villages of Shantou Chaonan are all above 1.0mg/L, prevalence of dental fluorosis is 76.99%; After water supply improvement until 2009, except village A, prevalence of dental florosis in other village decreased to the normal level. The prevalence of dental caries of control village is higher than that of fluorosis villages.Base on the dose-response relationship, BMDL of urine fluoride to prevalence of dental florosis,AKP,BGP,Z score is 0.71 mg/L,1.19 mg/L,0.56 mg/L,1.50 mg/L.Outer exposure level of fluoride in Shantou Chaonan is low, inner exposure level of village A which has the shortest water supply improvement time is higher than that of control village, inner exposure level of village D and C which have longest water supply improvement time is lower than that of control village.Combined with the results of same kind research, it is suggested that the biological exposure limits of urine fluoride in florosis area after water supply improvement should be≤1.5mg/L.Conclusion: Through long time water supply improvement in Shantou Chaonan, it has significant effect. Each indicator of health effect decreased to normal level. Biological exposure limits of drinking water fluoride and urine fluoride calculated by BMD method is safe and reasonable. There are 2.74% and 0.77% children have health risk in florosis area and normal area, it is predicted that 15～20 years after water supply improvement in florosis area, fluoride will not cause specific changes of health effect.