Mutation spectra in Salmonella TA98, TA100, and TA104 of two phenylbenzotriazole mutagens (PBTA-1 and PBTA-2) detected in the Nishitakase River in Kyoto, Japan

Abstract

Previous studies have identified two potent aromatic amine mutagens in the Nishitakase River, a tributary of the Yodo River, which serves as the main drinking water supply for the Osaka area in Japan. The two potent mutagens are 2-[2-(acetylamino)-4-[bis(2-methoxyethyl)amino]-5-methoxyphenyl]-5-amino-7-bromo-4-chloro-2 H-benzotriazole (PBTA-1) and 2-[2-(acetylamino)-4-[ N-(2-cyanoethyl)ethylamino]-5-methoxyphenyl]-5-amino-7-bromo-4-chloro-2 H-benzotriazole (PBTA-2). PBTA-1 and PBTA-2 are presumed to be formed from azo dyes discharged in a reduced form from dye factories to sewage treatment plants where they become chlorinated and are then discharged into the river. PBTA-1 and PBTA-2 account for 21% and 17% of the mutagenic activity of the Nishitakase River, respectively. Here we determined the mutation spectra induced by these two mutagens in TA98, TA100, and TA104 at 30–35, 8–10, and 2×, respectively, above the background. In TA98, the PBTA compounds produced identical mutation spectra, with 100% of the revertants containing the hotspot 2-base deletion of CG within the (CG) 4 sequence. In TA100, 73% of the revertants were GC→TA transversions, with most of the remaining being GC→AT transitions; the spectra produced by the two compounds in TA100 were not significantly different ( p=0.8). In TA104, as in TA100, the majority (83%–87%) of the revertants were GC→TA transversions, with most of the remaining revertants (11%–13%) being AT→TA transversions. Thus, 83%–87% of the mutations induced by the PBTA compounds in TA104 were at G/C sites. The mutation spectra produced by the two compounds in TA104 were not significantly different ( p>0.08). PBTA-1 and PBTA-2 are structurally similar and have similar mutagenic potencies and mutation spectra in the respective strains. The mutation spectra produced by the PBTA compounds (100% hotspot deletion in TA98 and primarily GC→TA transversions in TA100 and TA104) are similar to those produced by other potent aromatic amines, which is the class of compounds from which the PBTA mutagens derive.