Water Quality And Health Risk Assessment Before And After Water Improvement Project For The Endemic Fluorosis Areas In Hancheng

Hancheng is located in the transition zone between the Guanzhong Plain and the Loess Plateau in northern Shaanxi.It has an arid and semi-arid climate.Groundwater is an important source of drinking water in this area.Relevant departments found in daily drinking water quality monitoring that there was an unsafe drinking water problem with drinking water fluoride content exceeding the standard,and found drinking water-type fluorosis patients in endemic disease investigation.Therefore,the local water conservancy department carried out the water quality improvement project to reduce fluorine.The earliest water improvement project has been nearly 30 years.In this study,the water quality data for the fluorosis villages before water improvement were collected.Water quality data of monitoring points including the fluorosis villages were collected in 2020 after water improvement.The physical and chemical parameters of water before and after water improvement in villages with fluorine disease were compared and analyzed.The improved water quality evaluation method was used to evaluate the water quality before and after the modification.The Monte Carlo model was used to assess the uncertain health risks.The results show that:（1）The projects in fluorosis villages have been running well after the water reform.The fluorine content of the water in the repeated monitoring after the water reform meets the national drinking water standard.The existing drinking water-type fluorosis patients were all born before carrying out the water improvement project.The detection rate of dental fluorosis among children aged 8～12 years was significantly reduced.The water safety problem for residents suffering from fluorosis has been improved through the fluoride reduction and water improvement project.（2）Before and after the water improvement projects,the concentration of most chemical indicators and over-standard rate of each indicator concentration in the dry season is lower than that in the wet season.Theoretically,the water quality in the dry season is better than that in the wet season.The concentration of each index was within the standard limit of drinking water after water modification,while the different chemical indexes in each monitoring point exceeded the standard before water modification.The concentration of each chemical index was reduced and improved compared with that before the water treatment,especially the concentration of F^-was significantly lower than that before the water improvement.It is believed that the water improvement project can solve the safety problem of drinking water with high fluoride.（3）The water quality index method is combined with the deterministic health risk assessment method.The results showed that pollutants with a high risk to human health are calculated with a higher weight.Factors that contribute more to the health risk index have higher weight in the water quality index method.After water improvement,the water quality comprehensive index of the villages with fluorine disease was lower than that before water improvement,and the water quality grade was improved.It can be considered that the local fluorine reduction and water improvement projects have achieved certain results.To a certain extent,the safety problem of drinking water with high fluoride in the village was solved.（4）By comparing the possible health risks of drinking water to human body before and after water modification,the health risks after water modification are less than before water modification.Comparing the certainty and the uncertainty health risk evaluation results based on Monte Carlo method,it is found that most of the uncertainty health risk prediction results have a higher probability of exceeding the standard than the deterministic health evaluation index.In the sensitivity analysis,the concentration of non-carcinogenic factor F^-had the greatest impact on the total non-carcinogenic risk,and the concentration of carcinogenic factor Cr⁶⁺accounted for the largest proportion in the carcinogenic risk index,which was the same as the results in the deterministic health risk assessment.