Study On The Related Influencing Factors Of Incidence Of Coal-burning Polluted Endemic Fluorosis

Objective: To explore the environmental chemical elements thatrelated to the coal-burning polluted endemic fluorosis; to assess therelationship between fluorosis and the contents of some chemical elements(Cu, Zn, Ca, Mg and Fe) in human blood; to assess the impact of theinteraction between these chemical elements and urine fluoride on theoccurrence of fluorosis; to provide a scientific basis for the comprehensiveprevention and control of the disease.Methods:(1) ecologic study: Cluster random sampling was used and38towns were randomly chosen from the55towns of Wushan and Fengjiecounty.The prevalence of dental fluorosis among8~12years old childrenwas checked by Dean’s method. The prevalence rate was calculated in eachtowns.The contents of the following11chemical elements in soil wasmeasured: F, Zn, Cu, I, Se, Cd, Cr, As, Ni, Hg and Pb.The associationbetween the dental fluorosis and the chemical element contents in thesurface soil was analyzed by the Spearman rank correlation.Selected the research areas of high content level of Cd and F in Jianping town while lowcontent level of Cd and F in Dachang town in Wanshan county usingpurposive sampling.Using Spearman rank correlation to analysis theassociation between the contents of F and the contents of Cd,in soil,rocks,crops, water, hair and urine,in Jianping and Dachang town,respectively.(2)case-control study:Multi-stage stratified cluster random sampling was usedand200children and90adults were enrolled.Fasting blood and urinesamples were collected.The difference of the contents of chemical elements(Cu,Zn,Ca,Mg and Fe) in blood and urine fluorine between cases andcontrols were analyzed by t-test.The interaction between urine fluorine andthe contents of Cu, Zn, Ca, Mg and Fe in blood was analyzed by layeredOR,Breslow-Day homogeneity test and Cochran-Mantel-Haenszel method.Results:(1) the results of ecological study: In Wushan county, theprevalence of dental fluorosis was positively correlated with the contents ofF and Cd in the surface soil, and negatively correlated with the contents ofCu, Zn and Se. Correlation coefficient was1.0000,0.9053,-0.6617,-0.7353,-0.5143, respectively (P＜0.05). This was also true in Fengjiecounty and the correlation coefficient for association was0.9959,0.9298,-0.5728,-0.8308,-0.6533, respectively. In Wushan county, the contents ofurine F and urine Cd had a strong positive correlation, The contents ofurine F and Cd in hair had a weak positive correlation, And the contents ofF and Cd in hair had a strong positive correlation, too. The correlation coefficient was0.9114,0.4743,0.9506, respectively.(P＜0.05).(2) theresult of case-control study: In children, the blood Zn of cases (70.88±9.28μmol/L) was lower than controls (75.53±10.78μmol/L)(P＜0.05). Theblood Cu (30.28±2.58μmol/L) and urine fluorine (0.74±0.36mg/L) ofcases were higher than controls (28.45±4.05μmol/L,0.48±0.21mg/L)(P＜0.05). While in adults, blood Zn in cases (91.13±10.29μmol/L) was lowerthan controls (99.57±11.73μmol/L)(P＜0.05). Blood Mg, Fe and urinefluorine of cases (1.57±0.19mmol/L,8.17±1.01mmol/L,2.37±1.01mg/L)were higher than controls (1.46±0.16mmol/L,7.72±0.96mmol/L,0.92±0.85mg/L)(P＜0.05). After the control of the fluoride, there was asignificant difference of prevalence rate of fluorosis between groups withnormal and abnormal contents of blood Zn (χ~2=3.8217, P=0.0506), Ca(χ~2=13.7248, P=0.0002), Mg (χ~2=3.9778, P=0.0461). While the differencebetween groups with normal and abnormal content of blood Cu (χ~2=0.2165,P=0.6417) and Fe (χ~2=0.8052, P=0.3695) was not significant.Conclusions:(1) The prevalence rate of dental fluorosis in twocounties was positively or negatively associated with contents of F, Cd, Cu,Zn and Se in the surface soil. Further study on the relationship betweenthese chemical elements and endemic fluorosis is needed.(2) The contentsof F and Cd in biological samples from subjects of two towns werepositively correlated. The damages to human bodies caused by cadmiumpoisoning and fluorosis were quite similar, presented by yellow dyed teeth and osteoporosis. Cd may affect the pathogenic process of fluoride.(3)Thecontents of Zn was reduced in patients with coal-burning fluorosis in twocounties. This shows that fluorine may reduce content of Zn in humanbodies.(4)If the significant level was0.1, then there may exist aninteraction between urine F and blood Ca in pathogenesis of fluorosis. Thecontents of blood Zn, Ca, and Mg play an important role in the process offluorosis, and people in endemic areas should strengthen the detection ofthese elements.