Induction of gene mutation in mammalian cells by 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), a chlorine disinfection by-product in drinking water.

3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), a potent direct-acting Salmonella mutagen found in chlorinated drinking water, was tested in Chinese hamster ovary (CHO) cells for the induction of mutation at the hypoxanthine phosphoribosyl transferase locus to 6-thioguanine resistance (TGr). MX treatment of CHO cells for 3 h at 37 degrees C resulted in significant dose-related increases in mutant frequency. The lowest observed effective dose was 2.5 micrograms/ml, where the cloning efficiency estimated on the day after treatment was not affected. The relationship between the dose of MX and the frequency of TGr mutants was approximately linear over the range of 0-5 micrograms/ml with an estimated slope (+/- 95% confidence limits) of 7.2 +/- 2.6 mutants per 10(6) clonable cells per microgram/ml.