Objective To understand the kinds and distribution levels of disinfection by-products (DBPs) and their potential health hazards in drinking water in Hangzhou main urban zone.

Methods According to the Drinking Water Standard Inspection Method (GB/T 5750-2006), in wet season (May and August) and dry season (January and November) of 2014, the concentrations of 13 DBPs and relevant physical and chemical indices were determined in 40 water samples from five centralized water supply systems and five households (finished water and tap water) in Hangzhou main urban zone. The health risks of DBPs via drinking water were assessed based on the cancer risk assessment model recommended by U.S. Environmental Protection Agency (EPA).

Results Trihalomethanes (THMs)i.e. trichloromethane (TCM), chlorodibromomethane (BDCM), and dichlorobromomethane (DBCM) were the principal DBPs in drinking water in Hangzhou main urban zone, and the concentrations in finished water and tap water were 0.7-51.7 μg/L and 2.1-27.9 μg/L respectively. The concentrations showed no seasonal variation (all Ps>0.05) and were not associated with water temperature, pH, and residual chlorine levels, but a strong correlation with the concentration of ammonia nitrogen in finished water was found (correlation coefficient, 0.448-0.643). In addition, the values of carcinogenic risk for DBPs in finished water and in tap water were 3.00×10^-6-6.25×10^-5 and 4.17×10^-6-3.69×10^-5 respectively; the values of non-carcinogenic risk were 3.45×10^-3-6.72×10^-2 and 4.39×10^-3-3.38×10^-2 respectively. Carcinogenic risks were all contributed by THMs, and BDCM and DBCM were the main contributors; but for non-carcinogenic risks, the five kinds of DBPs had almost equivalent contributions.

Conclusion THMs are the principal DBPs detected in the drinking water in Hangzhou main urban zone in 2014. Both the potential carcinogenic and non-carcinogenic health risks induced by DBPs through drinking water are within the limits recommended by U.S. EPA.