the levels of two aromatic amine mutagens , 2-[2-(acetylamino)-4-[bis(2-methoxyethyl)amino]-5-methoxyphenyl]-5-am ino-7-bromo-4-chloro-2h - benzotriazole ( pbta-1 ) and 2-[2-(acetylamino-4-[n-(2-cyanoethyl)ethylamino]-5-methoxyphenyl]-5-a mino-7-bromo-4-chloro-2h - benzotriazole ( pbta-2 ) , were quantitatively analyzed in the yodo river system in japan . 
 the river water samples were collected at nine sampling sites from the yodo river system twice or three times between may and july in 1997 . 
 pbta-1 and pbta-2 in the river water samples were concentrated on blue rayon columns , partially purified by high - performance liquid chromatography ( hplc ) on reverse - phase columns , then quantified by hplc with an electrochemical detector . 
 the amounts of pbta-1 and pbta-2 in the water samples were < 0.01 - 1.91 and < 0.01 - 2.25 ng / l , respectively . 
 high levels of pbta-1 and pbta-2 were detected in the samples collected within 4 km downstream of two sewage plants , which are located along the banks of the nishitakase river , a tributary of the yodo river system , and these samples showed stronger mutagenicity in salmonella typhimurium yg1024 with s9 mix than the other water samples . on the other hand , 
 the river water samples from upstream of the sewage plant were weakly or not mutagenic and pbta-1 and pbta-2 were not detected . 
 these results confirmed that a major source of pbta-1 and pbta-2 in the yodo river system is effluent from the sewage plants and that discharged mutagens , including pbta-1 and pbta-2 , are diluted and/or decomposed while moving down the yodo river system.imagesfigure 1figure 2figure 3figure 4figure 5