Methylene-bridged polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants1 that are often found in even higher concentrations than the wellrecognized PAHs with bay-region methyl groups. 2 A number of PAHs with a methylene bridge traversing the bay region: see, eg, l5, l6-dihydro-l, ll-methanocyclopenta [alphenanthren-17-one (2): have been shown to exhibit potent tumorigenic activity. This somewhat unexpected observation ...