Development of quantitative comparative cytotoxicity and genotoxicity assays for environmental hazardous chemicals

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Mammalian cell asays can provide toxicological information that may be more relevant to human risk asessment than commonly used microbial tests. Rapid, semi-automated, quantitative mammalian cell cytotoxicity and genotoxicity assays were developed to analyze drinking water disinfection by-products (DBPs). These assays employ 96-well microplates; selected DBPs were analyzed with cultured Chinese hamster ovary (CHO) cells. The concentration of the DBPs that repressed 50% of CHO cell growth with a 72 h exposure was calculated as the %C1/2 value. Using these values the rank order (from highest to lowest cytotoxicity) was bromonitromethane, dibromonitromethane, tribromonitromethane, bromoacetic acid, dibromoacetic acid, and tribromoacetic acid. Genotoxicity analyses of the DBPs were conducted using the single cell gel electrophoresis (SCGE) assay. This assay detects genomic DNA damage at the level of the individual nucleus. Using SCGE genotoxic potency the rank order was bromoacetic acid> dibromonitromethane>>bromonitromethane>dibromoacetic acid>tribromoacetic acid. The relative cytotoxicity and genotoxicity of these agents were compared with Salmonella typhimurium. Studies of specific DBPs in mammalian cell systems are important to compare the toxicity of these hazardous water contaminants. Such knowledge is necessary for risk assessment and to assist in the formulation of public regulatory policies that protect the environment and the public health.