The third United Kingdom Environmental Mutagen Society collaborative trial: overview, a summary and assessment

An overview of the results of the third UKEMS collaborative trial with cultured mammalian cells is presented and their implications are discussed. Data suitable for statistical evaluation are generated by using the protocols which have been developed for the trial. The results for the three test compounds, ethyl methane sulphonate, benzo[a]pyrene and benzidine (BZD) from the nine participating laboratories demonstrated the essential requirement for replicate cultures in any adequate experimental design. Amongst the many practical points that are reinforced by this study are: (i) the number of cells to be sub-cultured during expression imposes a severe limitation on the use of surface attached cells; (ii) the importance of a careful determination of toxicity; (iii) that S9 levels may need to be varied; and (iv) that BZD is mutagenic only at the tk locus in L5178Y TK+/- cells. The 32P-post-labelling study with BZD reveals that no detectable DNA adducts were found with this agent even in L5178Y or HeLa cells. Thus the mechanism for mutagenesis in L5178Y cells remains to be elucidated.