Initiation/promotion studies with coal-derived liquids.

Fractions derived from solvent-refined coal-II (SRC-II) heavy distillate (HD) were tested for their skin tumor initiating activity. Basic (BF), basic tar (BTF), neutral tar (NTF) and polynuclear aromatic (PNA) fractions were prepared from HD by solvent extraction. These fractions were tested for their initiating activities by applying a single dose to the shaved back of male, CD-1 mice (Charles River, Portage, MI). Positive control groups were initiated with either dimethylbenz[a]anthracene (DMBA) or benzo[a]pyrene (BaP). Two weeks after initiation, all mice received twice weekly applications of 5 micrograms of phorbol myristate acetate (PMA) for a period of 24 weeks. Papillomas were noted and recorded for each animal at the time of PMA application. Heavy distillate and its fractions all showed initiating activity. However, the incidence of mice with tumors, the rate of tumor appearance and the total number of tumors varied with the test material. The tumor responses after initiation with HD,NTF and BTF were similar to that found with BaP, but lower than that with DMBA. Somewhat lower activity was found for BF and PNA. Even lower activity was found with a distillate boiling from 800 to 850 degrees F and no activity was found with a 300 to 700 degrees F distillate. These data are in general agreement with the results of long-term, skin painting assays, suggesting that initiation/promotion (I/P) may be useful for studying the tumorigenicity of coal-derived materials.