Seventeen samples of tap water in Bangkok and 2 neighboring provinces were collected in winter and summer, concentrated and tested for mutagenic activity using the Ames Salmonella mutagenesis assay. Preliminary results demonstrated that concentrated tap water exhibited clear mutagenicity towards S. typhimurium TA100 and YG1029, but not towards TA98 and YG1024, in the absence of S9 mix, and the addition of S9 mix markedly decreased the mutagenicity to both tester strains. Amberlite XAD-2 resin, but not blue rayon, was able to adsorb mutagens from water at pH 2.
Our data clearly demonstrated that all tap water samples prepared by chlorination of Chao Phraya River water were mutagenic to strain TA100 without S9 mix, inducing 3,351 ± 741 and 2,216 ± 770 revertants/l, in winter and summer, respectively. On the other hand, however, tap water samples prepared from ground water were not mutagenic. Furthermore, it was found that boiling for only 5 min and filtration through home purifying system containing activated charcoal and mixed resin units were very effective to abolish the mutagenicity of water. Storage of water also significantly decreased the mutagenicity, however, it took 2-3 weeks to totally abolish it. Additionally, we also found 1 out of 6 brands of commercially available bottled drinking water to be mutagenic, with about 26 % of the average mutagenicity of tap water.
The results in the present study clearly demonstrated that chlorinated tap water in Bangkok and neighboring provinces contain direct-acting mutagens causing capable of causing base-pair substitution. Boiling and filtration of tap water through home purifying systems may be the most effective means to abolish the mutagenicity. Some brands of commercial bottled waters may also contain mutagens which may be derived from tap water.
)