[On the interaction of polycyclic aromatic hydrocarbons and light with regard to its syncarcinogenic effects...

The rapidly growing pollution of the human biosphaere with potentially carcinogenic agents gives increased relevance to questions concerning the interaction of both chemical and physical agents in carcinogenesis. One such combination of environmental agents - that between polycyclic aromatic hydrocarbons and light - which heretofore has received little attention from workers in the field of environmental research, was investigated in the present paper. The phototoxic (cytotoxic) effects of carcinogenic aromatic hydrocarbons was demonstrated using ciliates of the species Tetrahymena pyriformis as the sensitive substrate. The experiments were conducted both with the chemically pure compounds and with native soot containing the adsorbed hydrocarbons. The following results were obtained: 1. Phototoxicity for ciliates of the highly carcinogenic benzo(a)pyrene may still be demonstrated in dilutions containing but 2 ppb (mug/l) of the substance, while the non-carcinogenic benzo(e)pyrene and fluorenthene are only weakly toxic in much higher concentrations. 2. The combination of benzo(a)pyrene and fluoranthene produced neither an additive nor a quenching effect, i.e., the resulting phototoxicity merely reflected the action of benzo(a)pyrene. 3. No phototoxic effect was observed in case of the fluorescent carcinogen, aflatoxin B1, in concentrations up to 200 ppb. This is taken to indicate that the property of fluorescence of carcinogenic substances by itself does not account for the phototoxic phenomenon. 4. The intense phototoxic activity of native soot ingested by the ciliates was shown to be dependent on the amount of polycyclic hydrocarbons contained. 5. Removal of polycyclic aromatic hydrocarbons from the soot particles by extraction with benzene resulted in the loss of phototoxic activity.