DISTRIBUTION OF SOIL ELEMENTS AND ITS RELATIONSHIP WITH KASCHIN-BECK DISEASE IN KBD AFFLICTED REGIONS——A CASE STUDY OF RANGTANG COUNTY, SICHUAN PROVINCE
Rangtang County, Sichuan Province where the prevalence rate of Kaschin-Beck disease (KBD) is relatively high and hence was selected as a typical case in this study to explore distribution characteristics of soil elements andits relationship to KBD. Soil samples were collected from two soil layers (0 ～20 cm and 20 ～40 cm) in natural and cultivated fields, separately for analysis of mechanical composition and total concentrations of nine soil elements. Resultsshowed that the subsoil is higher than the topsoil in contents of Fe2O3 , Co, Se and percentage of physical clay, but lowerin contents of Mo and percentage of physical sand. As the local natural soils are less disturbed by human activities, no significant difference was found on the physicochemical properties between different soil layers or soil profiles (p O 0.05 ).The distribution of Mo and Se elements in the soil led to poor crop uptake of the two elements, thus causing the local population, especially children, nutritional deficiency in Se and Mo, which is demonstrated to be closely related to KBD. Affecred by the parent materials and pedogenesis of the soils, Fe2O3, Co and Mn similar in physical and chemical properties, as well as Zn, Cu and Hg all showed a better positive correlation (p ＜ 0.01). However, no significant correlation was observed between these elements and the clinical prevalence of Kaschin-Beck disease. A total of 23 administrative villages involved in this study were divided into four groups by an ascending sequence in terms of clinical prevalence of Kaschin-Beck disease, i.e. Group Ⅰ (n = 6, incidence rate 14.02％ ～ 19.87％ ), Group Ⅱ (n = 6, incidence rate 24.62％ ～ 28.20％ ) , Group Ⅲ ( n = 6, incidence rate 28.45％～ 36.26％ ) and Group Ⅳ (n = 5 incidence rate 37.30％ ～ 53.66％ ). Due to the adsorption of Se by soil clay and Fe2O3, which are similar in distribution characteristics, the disease is getting more severe with decreasing soil clay, Fe2O3 and Se content in the soil. The distribution of Hg in soil was just contrary to that of Se. However, no evidence is confirmed that antagonism exists between Se and Hg in soil low in both.
SoilPhysical claySeleniumKaschin-Beck diseaseRangtang County
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