- There exists a growing need to establish a better in vitro model for evaluating PAH toxicity and carcinogenicity and to improve assessments of risk to human health, especially to the complex mixtures that exist in the environment. Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants due to the incomplete combustion of fossil fuels. Several PAH compounds are classified as known or probable human carcinogens and have been implicated in lung tumor formation in various in vivo models. This study investigates the mutagenic potential of soil samples from a Superfund creosote site contaminated with polycyclic aromatic hydrocarbons before and after remediation using an in vitro mammalian transgenic mutation assay. We hypothesize that contaminated soil samples have reduced mutagenic activity and associated cancer risk after thermal remediation to remove chemical contaminants. We further hypothesize the mutagenic potency for complex PAH mixtures in soils can be estimated from mutagenic activity of individual component PAHs. The MutaMouse FE1 lung cell line, an in vitro version of the lacZ transgenic rodent mutation assay, is metabolically competent and can be used to evaluate genotoxicity of DNA-reactive PAH chemicals to assess cancer risk. FE1 cells were treated with PAH mixtures extracted from soils at 5 concentrations for 6-hrs and cells collected for evaluation of cell viability and mutagenicity. Benzo[a]pyrene, a known mutagenic carcinogen, was included as a positive control. Genomic DNA was isolated from the exposed cells and the frequency of lacZ mutants were measured for each sample and concentration to calculate mutagenic potency in soil samples before and after remediation. The mutagenic potency for PAH mixtures was calculated and compared, using the RPF approach, to the calculated potency for individual PAH components to determine if the additivity model for risk assessment could be applied. The goal of this research was to improve upon the knowledge of cancer risk of PAHs in complex mixtures using an in vitro mammalian assay treated for mutagenicity. Further information on the toxicity of PAH mixtures are provided by the evaluation of additional endpoint analysis, by the like of a cytotoxicity assay and investigation of gene expression in metabolism by looking at CYP isozymes, oxidative stress and DNA damage markers. Cumulatively this information provides insight on the toxic and mutagenic potential of PAHs in mixture forms and identifies if they are in fact remediated to possess less potential cancer or toxic risk.