Abstract:

Objective To understand the levels of six disinfection by-products in drinking water in Dongcheng District of Beijing City from 2023 to 2024，including trichloromethane，dichlorodibromomethane，dichlorobromomethane，tribromomethane，dichloroacetic acid，and trichloroacetic acid，and to assess their health risks to the population. Methods From 2023 to 2024，collect the effluent from water plants in the jurisdiction，municipal terminal water from corresponding pipelines，and secondary water supply for chlorine disinfection byproduct detection. Use the health risk assessment method recommended by the US Environmental Protection Agency（USEPA） to evaluate the health risks of disinfection by-products exposed to adults through drinking water routes in the jurisdiction，and analyze the concentration differences of disinfection by-products in different water quality types（effluent water，municipal terminal water，secondary water supply），years，and water periods（wet season，dry season）. Results The detection rate of six chlorine disinfection by-products ranged from 81.88% to 100.00%. There were statistically significant differences in the concentrations of chlorodibromomethane，dichlorodibromomethane，and dichloroacetic acid among different water quality types（χ²=14.272，28.641，13.330，all P<0.01）. The three disinfection by-products had the highest concentration in factory water and the lowest concentration in municipal terminal water. There were statistically significant differences in the concentrations of dichlorodibromomethane，dichloroacetic acid，and trichloroacetic acid in different years（χ²=7.775，8.236，12.385，all P<0.01），and the concentrations of the three disinfection by-products were all higher in 2023. There were statistically significant differences in the concentrations of monochlorodibromomethane，tribromomethane，and dichlorodibromomethane in different water periods（χ²=13.125， 50.434，32.008，all P<0.01）. The concentrations of monochlorodibromomethane and tribromomethane were higher in the dry season than in the wet season，and the concentration of dichlorodibromomethane was higher in the wet season than in the dry season. The maximum R-value of 6 disinfection by-products had a carcinogenic risk of less than 1.00×10^-4，which was lower than the maximum acceptable risk specified by USEPA. Among them，chloroform had the highest carcinogenic risk，with a median R-value of 3.000×10^-5 and an R-value range of 0.002×10^-5-5.053×10^-5. Except for the median R value of bromomethane，which was less than 1.00×10^-6，the median R values of the other five chemical pollutants were all greater than 1.00×10^-6（0.591×10^-5-3.000×10^-5），indicating a certain carcinogenic risk but within an acceptable level. The non-carcinogenic risk of the six disinfection by-products was far less than 1，with chloroform having the highest non-carcinogenic risk. The median HQ value was 9.679×10^-2，ranging from 0.006×10^-2 to 16.299×10^-2. Conclusion The carcinogenic and non-carcinogenic risks of six disinfection by-products in drinking water in Dongcheng District of Beijing City are within an acceptable range，with trichloromethane as the key indicator of concern.

Key words: Drinking water, Chlorine disinfection, Disinfection by-products, Health risk assessment