Objective:To analyze the types and distribution characteristics of elements in drinking water from endemic fluorosis areas with water improvement in Xi'an City, understand the relationship between fluoride and various elements, and conduct health risk assessment on potential high-risk elements.Methods:From May to June 2017, one endemic fluorosis area with water improvement (Gaoling District, Huyi District, Lintong District) was selected according to the northeast, the southwest and the due east directions of Xi'an City as the survey area. Sixteen endemic fluorosis villages were selected from each endemic area, and 2 water samples were collected from each endemic village to detect fluoride and 12 elements such as chromium, manganese, ferrum, copper, zinc, arsenic, selenium, molybdenum, cadmium, antimony, barium, and lead. Hygienic evaluation was conducted according to national standards, and the potential high-risk elements (arsenic, molybdenum) were assessed for health risk through the health risk assessment model recommended by the National Environmental Protection Agency of the United States.Results:The water samples from the endemic fluorosis areas in Xi'an City mainly contained seven elements: barium, ferrum, molybdenum, arsenic, zinc, manganese, and chromium. The content of copper and selenium was relatively low, while the content of cadmium, antimony, and lead was extremely low. The fluoride content in water samples from Gaoling District and Lintong District was relatively high, and the fluorine, arsenic, molybdenum elements was pairwise positively correlated ( P < 0.05). The molybdenum element in water samples from Lintong District exceeded 9.38% (3/32). The fluoride in the water samples of Huyi District was relatively low, and the arsenic, molybdenum elements was positively correlated ( r = 0.84, P < 0.001), and the arsenic element exceeded the standard by 25.00% (8/32). The main health risk of drinking water in endemic fluorosis areas with water improvement in Xi'an City was arsenic exposure, with children at a higher risk than adults, and the areas of Huyi District, Lintong District, and Gaoling District declined, the risk of cancer (CR) of Gaoling District was < 10 -4 and hazard quotient (HQ) was < 1. However, in the areas of Huyi District and Lintong District (except HQ of adults), there was a higher risk (CR > 10 -4, HQ > 1). Children in one endemic fluorosis village in Lintong District had a higher non carcinogenic risk of molybdenum (HQ > 1). Conclusions:The drinking water in endemic fluorosis areas with water improvement in Xi'an City mainly contains 7 elements, especially arsenic and molybdenum, which need to be regularly monitored. Some areas have high health risks of arsenic in water, and monitoring, management, and related epidemiological investigations need to be strengthened. At the same time, it is necessary to actively monitor other toxic and harmful substances that may be introduced during the water improvement process to prevent the occurrence of secondary health problems.

Objective:To observe the application of case-based problem-based learning (PBL) teaching in the postgraduate education of radiography.Methods:A total of 48 postgraduates in the Batch 2019/2020 of professional masters majoring in radiography were selected as research objects, and they were divided into observation group ( n=24, Batch 2020) and control group ( n=24, Batch 2019). The students in the control group were taught by traditional teaching, and the students in the observation group were taught by case-based PBL teaching method. The differences in imaging diagnosis level and structured assessment scores of the two groups of students and their evaluation of the teaching process were analyzed. SPSS 20.0 was applied to perform the t test and chi-square test. Results:The imaging diagnosis ability of the students in the observation group (84.98±7.51) was significantly higher than that in the control group (78.21±6.96) , and the difference was statistically significant ( P<0.05). The students in the observation group had higher ability of imaging diagnosis skills and case analysis and diagnosis during the structured assessment ( P<0.05). The students in the observation group had higher overall satisfaction with the teaching process than those in the control group ( P<0.05). Conclusion:The case-based PBL teaching is of great help in improving the clinical thinking and imaging diagnosis ability of postgraduates majoring in radiography. In the application, it is necessary to continuously improve and supplement the teaching implementation plan according to the teaching evaluation and feedback.