Assessing the use of known mutagens to calibrate the Salmonella typhimurium mutagenicity assay: I. Without exogenous activation

Abstract

There has been an increasing need in genetic toxicology to progress from strictly qualitative tests to more quantitative tests. This, in turn, has increased the need to develop better quality assurance and comparative bioassay methods. In this paper, two laboratories tested 10 Salmonella mutagens in order to determine the usefulness of selected chemicals as potential reference materials to calibrate the Salmonella assay. If variance within a bioassay is sufficiently low and the rankings of the compounds are of acceptable consistency, the chemicals later could be evaluated for use as standard control compounds, as audit materials, and as standard reference materials for comparative bioassay efforts. The results demonstrated that the chosen chemicals (with the possible exception of dimethylcarbamylchloride) provide such consistent results in the Salmonella mutagenicity bioassay that they can be used for semi-quantitative calibration and as possible bioassay controls, special audit chemicals, and potentially as reference standards in comparative bioassay efforts. Reference standards, whether used as audit materials or in comparative bioassays, must be used concurrently with the test substances of interest; used without bias; used in a standardized, highly controlled bioassay; and be tested across an appropriate dose range. The study also shows that when these compounds are used as reference standards much care must be given to the number and spacing of doses if highly reproducible slope values are to be generated. We recommend use of a pilot test to establish a dose range for definitive tests and the placement of doses for the definitive tests within the first half of the linear dose-response curve. For appropriate comparisons, one should replicate the tests using the defined dose range and analyze the results in a non-biased statistical manner.