Mutagenicities of Bangkok and Tokyo river waters.

Samples of water from the Chao Phraya river and some connected canals in Bangkok, Thailand, and from the Sumida and Ara rivers in Tokyo, Japan, were tested for mutagenicity using blue rayon to adsorb the mutagens. The samples from the Chao Phraya river and connected canals at sites located 50-150 km from the river mouth taken in May 1993 showed a mutagenicity of 87-1213 revertants per 0.05 g blue rayon extract towards S. typhimurium YG1024 in the presence of S9 mix. Samples from most sites taken in December 1993, which follows the rainy season, showed a lower mutagenicity than those taken in May, possibly due to dilution by the larger volume of water in the river and canals in December. Water samples from the Sumida river were collected in July 1993 and February 1994, and those from the Ara river in January 1994. Mutagenicity of samples from all sites of the Sumida and Ara rivers, which were located 2-30 and 2-20 km, respectively, from the river mouth was also clearly detected in the presence of S9 mix and did not differ much, being 155-748 revertants of YG1024 per 0.05 g blue rayon extract. These results demonstrated that the water in all three rivers contained some frameshift mutagens.