IDENTIFICATION OF ENVIRONMENTAL 



GENETIC TOXICANTS 

 WITH CULTURED MAMMALIAN CELLS 



Alexander R. Malcolm, Robert R. Young, 

 and Carolyn J. Wilcox 



U.S. Environmental Protection Agency 



Environmental Research Laboratory 



Narragansett, R.I. 02892 



ABSTRACT 



Experiments designed to detect small-scale mutations leading to auxotrophy 

 were carried out in vitro with the Chinese hamster ovarian (CHO) cell system 

 (5-bromodeoxyuridine/visible light selection) initially described by Puck and 

 Kao (43). The system was standardized with ethylmethanesulfonate (EMS), a 

 known mutagen previously demonstrated to be active in CHO cells (27), and 

 5-bromodeoxyuridine (BrdU), another known mutagen (7) utilized in the 

 selection procedure, but not previously evaluated for mutagenic activity in the 

 CHO Cell/BrdU-VL assay. Both EMS and BrdU routinely yielded glycine, 

 hypo xanthine or triple-requiring (glycine/hypoxanthine/thymidine) 

 auxotrophs and showed dose response. For a series of inorganic compounds 

 known to be or suspected of being genetic toxicants, statistically significant 

 numbers of auxotrophs were obtained only with the chloride salts of cadmium 

 and manganese. Neither cadmium nor maganese were consistently mutagenic, 

 cadmium showing activity in about 20 percent of experiments, manganese in 

 50 percent of experiments. It was not possible to demonstrate dose response 

 with these compounds. A water extract of JP-5 jet fuel was also found to be 

 mutagenic in a single test. Variant cell types other than auxotrophs were 

 isolated from cell populations treated with three different carcinogenic agents 

 (EMS, Cr03, PbAc2.3H20) but not from control experiments. These cells, 

 exhibiting either a rounded cell morphology or potential contact inhibition, 

 may reflect mutation in additional loci of possible value as genetic markers. 

 Other data are presented to illustrate special problems associated with the 

 application of in vitro cell systems. 



INTRODUCTION 



Serious concern for the possible effects of genetic toxicants in the 

 environment developed approximately a decade ago with the discovery of 



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