The authors adapted microtitration techniques to the SOS Chromotest, and thereby established a simple and reliable modified genotoxicity test: the Microtitration SOS Chromotest. This test employs microtitration techniques and photometric analysis with numerical readout. These data are integrated into the computerized data processing program Statistical Analysis System to obtain genotoxicity and toxicity results of a chemical or chemical mixture within 16 h. In order to test the applicability of the new system, the genotoxicity and toxicity of 22 pesticides were studied. A two‐sample t test was employed to determine the level of significance (p < 0.05). Nine of the pesticides were found to induce the SOS response in Escherichia coli cells. Their relative degrees of induction based on SOS inducing potency values are as follows: captafol > captan > folpet > dinoseb > ferbam > linuron > alachlor > phosmet > cacodylic acid. The addition of rat liver S9 mix does not transform the nongenotoxic pesticides tested into genotoxic forms but significantly decreases the inducing ability of most positive pesticides. The Microtitration SOS Chromotest is rapid and efficient in providing evidence for decision‐making related to cleanup of chemical spills and discharges where time is a critical factor. This method maintains its high accuracy and sensitivity compared with conventionally used assays. The studies of pesticide genotoxicity using this test confirm the applicability, reliability, and sensitivity of the Microtitration SOS Chromotest as a simple, efficient, and rapid genotoxicity prescreening system as well as an excellent research tool for genotoxic mechanism studies.

OBJECTIVEThis method is intended t o be used for screening and evaluating chemicals and samples for genotoxicity by monitoring E . coli p-galactosidase (associated with SOS response) and alkaline phosphatase activity (representing the samples' toxicity). SCOPEThis method is applicable for testing (i) water-soluble compounds, (ii) water-insoluble but DMSO-soluble compounds, and (iii) environmental water samples and sediment extracts. PRINCIPLE3.1 3.2In E . coli some of the responses induced by DNA-damaging agents generate a set of functions known as the SOS responses. An operon fusion associates P-galactosidase gene (lac Z) with the sfiA gene, an SOS function involved in cell division inhibition. Thus, whenever the SOS function is activated because of bacterial DNA damage, the P-galactosidase biosynthesis will be turned on. The addition of the enzyme substrate, o-nitrophenyl-P-D-galactoside will result in the production of a yellow-colored compound, nitrophenol, which can be easily measured colorirnetrically .