MUTAGENIC EFFECTS OF STYRENE AND STYRENE OXIDE

Styrene and its presumed metabolite styrene oxide were tested in the Salmonella/liver-microsome test on the tester strains TA1535, TA1537, TA1538, TA98 and TA100 of Salmonella typhimurium. Styrene oxide, in the concentration range 1-10 μmoles per plate, was mutagenic on TA1535 and TA100, both in the absence and the presence of a rat-liver microsomal system. Styrene, on the other hand, in the concentration range 10-3 to 15 μmoles per plate, was not mutagenic in any of the tester strains, regardless of the presence or absence of a 9000 × g supernatant of rat-liver homogenate. Two differently induced microsomal fractions were used, one induced with Aroclor 1254 and one with another PCB mixture, Clophen C. Styrene was negative in both systems. Styrene is presumed to be metabolized to styrene oxide, and in an attempt to potentiate the possible mutagenicity of styrene, two inhibitors of the metabolic breakdown of styrene oxide were added to the homogenates. They were 1,1,1-trichloropropene 2,3-oxide, an inhibitor of epoxide hydratase and diethyl maleate, an inhibitor of the glutathione conjugation pathway. This did not result in any mutagenic effect of styrene in the test. Our conclusion is that in the Salmonella/liver-microsome test, styrene oxide is mutagenic whereas its presumed precursor in the presence of a metabolizing system is not. This might indicate that when styrene is tested together with a rat-liver microsomal fraction, the concentration of styrene oxide is too low to be detected as mutagenic. © 1979.