GENOTOXIC ACTIVITY DETECTED IN SOILS FROM A HAZARDOUS-WASTE SITE BY THE AMES TEST AND AN SOS COLORIMETRIC TEST

Ten soil samples from a hazardous waste site were compared for their g enotoxic activity by the Ames test (Salmonella reverse mutation assay) and a modified SOS colorimetric test. Polynuclear aromatic hydrocarbo ns known to produce frameshift mutations were found in high levels in the soils. Salmonella typhimurium TA98, sensitive to frameshift mutati ons, was selected as the Ames tester strain. Escherichia coli K12 PQ37 (sulA::lacZ) was the SOS tester strain. Organic extracts were prepare d from the soil samples by Soxhlet extraction. One set of the soil sam ples was extracted with methylene chloride and a second set with cyclo hexane. Two criteria from reproducible dose-related increases in respo nse to the soil were used to compare the positive responses: 1) the co ncentrations required for doubling responses and 2) a minimum concentr ation required to produce statistically significant increases from bac kground controls. Analysis of variance indicated that with S9 mix, Ame s and SOS results were similar for the same soils and solvent extracti ons. However, without S9 mix, the SOS test was significantly more sens itive than the Ames test to the genotoxins extracted from the soils. B oth the Ames and SOS tests detected lower concentrations of genotoxins in methylene chloride than in cyclohexane extracts. The simplicity of the method, reduction in expenses, and results within 1 working day a ll contribute to the advantages of the SOS test. (C) 1993 Wiley-Liss, Inc.