Objective: To investigate the distribution characteristics of trichlormethane in school drinking water in Jiangsu Province, and to evaluate the health risks and influencing factors of students exposed to trichlormethane, so as to provide a scientific basis for the disinfection and safety of school drinking water. Methods: A total of 315 schools (123 primary schools, 142 junior high schools, 20 high schools, and 30 universities) in Jiangsu Province were selected by a stratified sampling method. Water samples in the wet period (from July to September) of 2023 and in the dry period (from January to March) of 2024 in each school were collected, and 630 drinking water samples were collected. According to the Standard Examination Methods for Drinking Water (GB/T 5750-2023), drinking water samples were analyzed for trichlormethane, and the health risks of trichlormethane exposure in drinking water for students were assessed using the health risk assessment method recommended by US Environmental Protection Agency. The Kruskal-Wallis H rank sum test and Mann-Whitney U test were performed to analyze concentrations and health risks of trichlormethane in school drinking water in different groups. Results: The concentration of trichlormethane in school drinking water in Jiangsu Province was 8.9 (4.6, 14.0) μg/L. The carcinogenic risk of trichlormethane in school drinking water was 9.8×10 -6 (5.3×10 -6 , 1.7×10 -5 ), which was an acceptable low risk. The amount of drinking water per unit body weight and the concentration of trichlormethane in tap water samples were important factors affecting the carcinogenic risk in drinking water for students. Comparison of carcinogenic risks exposed to trichlormethane in drinking water were as follows:primary school students in lower grades had the highest risk of carcinogenesis, with a risk of 1.2×10 -5 , the wet period (1.3×10 -5 ) >the dry period (7.6×10 -6 ), river source water (1.0×10 -5 ) >lake source water (6.8×10 -6 ), liquid chlorine disinfection (1.1×10 -5 ) > sodium hypochlorite disinfection (9.3×10 -6 ), conventional treatment (1.4×10 -5 ) > advanced treatment (9.6×10 -6 ), with statistically significant differences ( Z=88.1, 3.7 , -3.2, -2.7, P <0.05). The non carcinogenic risk of trichlormethane in school drinking water was 1.4×10 -2 for less than 1, and the non carcinogenic risk was acceptable. Conclusions The carcinogenic and non carcinogenic risks of trichlormethane in school drinking water are acceptable in Jiangsu Province, and the primary school students in lower grades are key indicators for risk management of trichlormethane in drinking water. According to the characteristics of the source water, appropriate disinfection methods and water treatment processes are selected to reduce the content of trichlormethane and control health risk.

The Standards for drinking water quality(GB 5749-2022), which has taken effect on April 1, 2023, stipulates that limit values of aesthetic and chemical characteristics of drinking water can be temporarily adjusted in emergencies. However, the national standard does not clearly specify the adjusted period and limit values. This study is based on the principle that the human body will not cause acute toxic damage during short-term exposure, considering the acceptability such as chromaticity, smell, and taste in drinking water, referring to the drinking water quality standards of different countries and regions including the World Health Organization, the United States, the European Union, Japan, Australia, etc. We discussed the limited values during emergencies for 21 aesthetic and chemical characteristics from GB 5749-2022 to guaranine the drinking water safety and human health in emergencies.

The Standards for drinking water quality(GB 5749-2022), which has taken effect on April 1, 2023, stipulates that limit values of aesthetic and chemical characteristics of drinking water can be temporarily adjusted in emergencies. However, the national standard does not clearly specify the adjusted period and limit values. This study is based on the principle that the human body will not cause acute toxic damage during short-term exposure, considering the acceptability such as chromaticity, smell, and taste in drinking water, referring to the drinking water quality standards of different countries and regions including the World Health Organization, the United States, the European Union, Japan, Australia, etc. We discussed the limited values during emergencies for 21 aesthetic and chemical characteristics from GB 5749-2022 to guaranine the drinking water safety and human health in emergencies.

Time-series and case-crossover are two main study designs in environmental epidemiology. However, due to the differences in design principles and model construction between the two analyses, the results of the two analyses may not be consistent. Herein, we examined the short-term effect of cold spells on cardiovascular mortality in Nanjing using both time series and case-crossover analyses, aiming to provide a basis for the selection of appropriate research design in environmental epidemiology.
Humans ; Cross-Over Studies ; Time Factors