| Abstract: | The wastewater contained mutagens which induced mutations in Salmonella typhimurium TA1535, TA1538, TA98 and TA100. By the use of nitroreductase-proficient and -deficient tester strains, it was possible to demonstrate that the mutagens were to a great extent aromatic nitro compounds. 30-40% of the mutagenicity could be related to the 16 identified nitroaromatic compounds. Although 13 of these induced mutations, one single compound, 3,5-dinitrobenzoic acid, was responsible for more than 80% of their total mutagenicity. p-Nitrobenzoic acid was used for further studies of the enzymatic nitroreduction leading to the formation of reactive intermediates. The bacterial enzymes and the active metabolites did not seem to be oxygen-sensitive, as the mutagenicity was decreased when anaerobic incubation was applied. The addition of dicoumarol resulted in a decreased effect, indicating that bacterial DT diaphorase or an enzyme with similar properties is responsible at least in part for the activation of this compound. Under our experimental conditions rat-liver enzymes were not able to produce any detectable amounts of mutagenic metabolites of p-nitrobenzoic acid when the nitroreductase-deficient strain TA100NR was used. |
