Abstract
In order to assess the potential hazards to human health and aquatic ecosystem, we examined the mutagenic activity of sewage effluents, river waters, sediments and drinking water collected from the Yodo River system, Japan. We also compared the levels of mutagenic activity with the levels of 2-phenylbenzotriazole (PBTA)-type mutagens formed from corresponding dinitrophenylazo dyes via reduction and subsequent chlorination. We assessed mutagenicity in the O-acetyltransferase-overexpressing frameshift strain YG1024 of Salmonella with S9 mix. Sixty-six samples among 133 adsorbates (50%) obtained by the blue rayon hanging method collected from 1996 to 2005 were classified as extreme mutagenicity with more than 100,000 revertants per g blue rayon equivalent (BRE). The average mutagenicity of both sewage effluents and river waters at sites located below sewage plants was 382,400 revertants per g BRE (n=86), which was 4.4 times as higher than the downstream river waters (87,900 revertants per g BRE, n=47). PBTA-1 was detected in 33 samples among 76 (43%), and PBTA-2 was detected in 66 samples among 76 (87%), however, the concentration of these compounds fluctuated widely among the samples. Average concentrations of PBTA-1 and PBTA-2 were also much higher in sewage effluents and river waters at sites located below sewage plants (n=50, PBTA-1, 24.1 ng/g BRE; PBTA-2, 88.4 ng/g BRE) than they were in downstream river water samples (n=26, PBTA-1; 1.3 ng/g BRE, PBTA-2; 19.7 ng/g BRE). PBTA-1 and PBTA-2 accounted for 6% and 26% on average, respectively, of the total mutagenicity in all samples analyzed. Based on the concentrations of the PBTA-type mutagens and the effluent volume discharged from three sewage plants, we estimated that ~5 kg/year of PBTA- type mutagens including PBTA-1, PBTA-2, PBTA-3, PBTA- 4, PBTA-6, PBTA-7 and PBTA-8, were discharged from three sewage plants into rivers. Further studies showed that these PBTA-type mutagens in river water might not easily accumulate in the river sediment and these PBTA-type mutagens were not detected in drinking water. In the final study, we monitored quantitatively the mutagenic potency of water samples collected at twelve sites, including six sites mentioned above, from the Yodo River system using Sep-Pak C18 cartridge columns and Blue-Chitin columns. The average mutagenic activities recovered by these columns were 10,000 and 5,800 revertants/L. These findings demonstrate that the Yodo River system has been continually and heavily polluted with not only polycyclic planar mutagens, but also by a wide range of chemical mutagens released from sewage plants located along the tributaries for many years.
