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Abstract
Coal tars, which are byproducts of coal gasification, are complex mixtures of chemicals including polycyclic aromatic hydrocarbons. Occupational exposure to coal tars is associated with a higher risk of cancer. The risk posed by environmental coal tars, and related oil tars, which may involve prolonged exposures to low doses, is not known. While this risk may be inferred from a knowledge of the concentration and potency of known carcinogenic components, the complexity and incomplete chemical analysis of coal tars lead to estimates with large uncertainties. In order to assess risk with greater certainty, laboratory studies were conducted to evaluate cancer induction following oral administration of coal tars. The appropriateness of these animal data to humans was evaluated in studies of the effects of these tars on genotoxicity, metabolism and gene expression. Our data suggest that the potency of coal tars cannot be predicted accurately from an understanding of the biological or carcinogenic effects of a few of its components. Carcinogenic effects are different in different strains of mice and vary with route of exposure and dose rate. The carcinogenic potency of coal tars appears to be modulated by the contributions of non-carcinogens in the mixture.