AbstractThe polyhalogenated aromatic hydrocarbons (PHHs), consisting of the chlorinated and brominated biphenyls, dibenzo‐p‐dioxins and dibenzofurans, are important environmental contaminants affecting both wildlife and humans. Although the biological effects due to acute or chronic exposure to these compounds have been extensively investigated with animal models, relatively little is known concerning the long‐term ramifications of such exposure due to the persistent body burdens of some PHH congeners. This review examines the persistent effects of these contaminants for two biological end points: tumor formation and induction of cytochrome P‐450‐associated mixed function oxygenases in target tissues. Literature and data are presented that indicate that retained PHH congeners continue for many months to exert biological effects that contribute to tumor development in rodent livers and lungs. Effects of specific congeners, retention profiles of these congeners in target tissues and the long‐term induction of cytochrome P‐450 IA1‐associated enzyme activity are all consistent with activation of the Ah receptor's being an integral part of the tumor pro
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