Hydrogeochemical Features And Disease-related Analysis In Kaschin-beck Disease Area, Zamtang County, Northwest Sichuan Plateau

The pathogeny of Kaschin-Beck Disease is very complex, and it is difficult to get unified recognition on the research of pathogeny in a short term, but it is an extremely urgent and imperative task to relieve patients'sufferings from KBD in Kaschin-Beck disease areas. Based on the common grounds of various etiological doctrines, the environmental factors, especially the hydrogeochemical factors in the typical area hit by KBD—Zamtang County in the northwest Sichuan Plateau, were studied in this paper, to provide scientific evidences and guides for comprehensive prevention and treatment of KBD.Firstly, features of geological environment and hydrochemistry characteristic in KBD area in China were summarized based on documentary surveys and investigation of patients'conditions. Secondly, the geological and hydrogeochemical environment of Zequ River and Duke River were studied through the quality analysis of the surface water, shallow groundwater (well water and spring water), and drilling groundwater (prospecting-mining wells) in Zamtang County. Thirdly, the relationship of KBD distribution with geological environment, especially hydrogeochemical environment was analyzed using statistical methodology, and an influencing factors model was established. Finally, measurements to prevent and treat KBD from the prospective of hydrogeochemistry were presented.The study mainly obtains results and conclusions as follows:(1) The definition of disease index is introduced to indicate conditions of KBD, and the feasibility of this indication is conducted with statistical methods. Apart from one non-disease area, Rangke Town, KBD are very serious in other eleven townships of Zamtang County. The disease index of Zequ River is 31.0, while that of Duke River is 23.96. Based on features of basin distribution, conditions of KBD are more serious in upstream areas than in downstream areas along the main stream basins for the characteristic of shallow cutting, meandering stream developed and runoff short in upstream areas.(2) Ground water in Zamtang County is divided into two categories: pore-space water in loosening rocks and bedrock fissure water. Pore-space water is mainly distributed in floodplain area, terrace and accumulation fan along the Zequ River, accounting for 0.71% of the whole county area. Bedrock fissure water is the most widely distributed underground water in the county, which can be further classified into two segments: weathering mesh fissure water and structural fissure water.(3) Constant ions of water in Zamtang County primarily are HCO₃^-, Ca²⁺, Mg²⁺, etc. Surface water and shallow groundwater in the county shows the low TDS characteristic less than 150mg/L, and its average amount of constant ion is less than the background value in Dadu River and Songpan non-disease area. Major ions and TDS of water in the county both show the regular of surface water < shallow groundwater <drilling underground water, indicating deep circulation groundwater represented by drilling water has long circulation route and can increase TDS of drinking water effectively.(4) Compared with the river water in source region of Yangtze River, trace elements of water in Zamtang County shows enrichment features generally, demonstrating the law that trace elements in the Zequ River are more than those in the Duke River. According to different sources of water, the density of trace elements is ranked roughly as: water from brooks>water from main steams>well water>drilling water>spring water, but in terms of specific elements, trace elements in different sources of water mentioned above are short of law with great difference.(5) Humic amount in the Zamtang County shows positive correlations with humic acid, fulvic acid and index of COD_Mn. According to river basins, total volume of humic acid in the Zequ River exceeds that in the Duke River. Specifically speaking, total volume of humic acid in the Zequ River ranges from low to high: drilling water<water from main streams<spring water<water from brooks<well water; while total volume of humic acid in the Duke River ranges from low to high: drilling water<average volume of river basins< water from main streams<water from brooks<spring water.(6) There is a relationship between geological environment in the Zamtang County and disease index of KBD as: disease index of the low mountains of erosion plateau is the highest, the second is the denudation hummocky plateau, and the lowest is the erosion alpine canyon; disease index in the mudstone areas is lower on the whole, while index in the other sand-slate areas is roughly higher. Among the three types soil of Zamtang County, disease index in brown soil and dark brown soil is the highest, the second is the countryside covered by meadow soil and disease index in the countryside with cinnamon soil is relatively lower. (7) For the purposes of this sample, it is found that KBD in the Zamtang County has a less obvious relationship both with trace elements and organic stuff respectively. Through the analysis of hydrogeochemical factors affecting KBD, the obviously negative correlation between KBD and constant index represented by TDS is obtained. Therefore, low TDS plays an essential role in KBD, but the trace elements and organic stuff has on unremarkable influence on KBD.(8) A hydrogeochemical influence model of KBD in Zamtang County is designed, taking mineralization and logarithm of constant ions as independent variables, and disease index as dependent variables. Simulation effect of the influence model is good. The influence model of Zequ River is y=149.687-23.852lnx, and the model of Duke River is y=104.478-16.592lnx (y stands for disease index; x stands for TDS); on the contrary, simulating effects of county structure is unsatisfying, indicating TDS is the main but not only factor of KBD, other geological environment factors or life-style can also have some impacts on KBD.(9) From the view hydrogeochemical point, some effective prevention approaches were put forward, such as safe water supply from deep well, immigration settlement and transferring children to non-disease areas to receive education, etc. Combining the correlation analysis of geological environment and conditions of KBD, the study also designs a feasible evaluation model of immigration settlement and site selection.