- quality controls of S9 (e.g., enzymatic activity, sterility, metabolic capability): Every S9-batch is tested for its metabolic activity by the use of specific substrates, requiring different enzymes of the P450-isoenzyme family. The mutagenicity of 2-aminoanthracene, benzo[a]pyrene, and 3-methylcholanthrene is thus determined once for every S9-batch. Clear increases in the number of revertants for S. typhimurium TA 98, TA 100, and TA 1537 with all positive controls and for TA 1535 with 2-aminoanthracene are used as an acceptance criterion for each S9-batch. In this study 2-aminoanthracene, and benzo[a]pyrene for TA 102, are used as the concurrent positive controls for the different strains in the presence of S9 mix.