Background Shanghai is an international megacity, where the increasing demand for drinking water of its large population bring into focus the safety of drinking water.
Objective This study evaluates the safety of drinking water in the main urban area of Shanghai through the mutagenicity analysis of organic substances in drinking water.
Methods In the dry season (from December 2015 to February 2016), level season (from March to May 2016), and wet season (from June to September 2016), samples of source water and finished water were collected from three water plants that draw water from Qingcaosha Reservoir, a water source that supply for the main urban area of Shanghai, and samples of pipeline water and tap water were collected at the monitoring points in the main urban area (including 10 monitoring points in 7 districts located in west of the Huangpu River). Samples were collected in three periods, once in each period, and 5L each time. XAD-2 absorbable resin was used to enrich the nonvolatile organic matter in water samples, setting low, medium, and high (0.25, 0.50, 1.00 L·dish-1) dose groups, and the potential mutagenicity of Salmonella typhimurium TA98 strain and TA100 strain was detected by bacterial reverse mutation assay. TA98 strain was used to detect frameshift mutation, while TA100 strain was used to detect base substitution mutation, and activated metabolic system (S9) was added to determine whether there were indirect mutagens in water samples.
Results Among the collected water samples, four samples were positive for TA98 strain in the bacterial reverse mutation assay, but were not mutagenic with TA100 strain, and the positive results only showed in the groups without activated metabolic system (-S9). In regard to water periods, the positive rate was higher in dry season (50%), followed by level season and wet season (25%). In regard to sample types, the positive rate of source water was higher (100%), followed by finished water (33.3%), and both pipeline water and tap water samples were negative. There was a significant difference in the reverse mutation ratio (MR) between -S9 and +S9 of TA98 strain in the same water sample (P < 0.05). The MR values of TA98 strain in different water periods (P < 0.05) showed significant differences; the MR values of TA100 strain in different water periods were significantly different (P < 0.05). There were significant differences in MR values of TA98 strain among different types of water samples (P < 0.05). The MR values of TA100 strain did not reach the positive standard, but the change trend was consistent with the values of TA98 strain.
Conclusion The nonvolatile organic compounds in tested drinking water of Shanghai are a kind of direct mutagenic substances which can cause frameshift mutation. The potential mutagenicity of drinking water is higher in dry season, followed by level season, and lower in wet season. In different types of drinking water, source water has strong potential mutagenicity, followed by finished water, and pipeline water and tap water have no mutagenicity.
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