AN ATTEMPT TO IMPROVE THE SOS CHROMOTEST RESPONSES

The SOS Chromotest was carried out on leachates of ten industrial wast es with the standard procedure and a miniaturized version with micropl ates. The two methods gave identical results in nine samples (eight ne gative and one positive). A simple additional manipulation is describe d for the identification of the false positive response that is freque ntly observed with complex mixtures. It involves challenging the SOS C hromotest bacteria with samples (having previously shown a positive ge notoxic response) just before the enzymatic activities (i.e. beta-gala ctosidase and alkaline phosphatase) are estimated colorimetrically. Th is additional step eliminates discrepancies between the results for th e standard and the miniaturized procedures.