Skin-tumor initiation activity of coal liquids with different boiling-point ranges

High-boiling coal liquids from the solvent-refined coal-I and -II (SRC-I, -II) processes, respectively, were fractionally distilled. In the case of SRC-I process solvent (PS), 50 degrees F distillation cuts were obtained between 550 and 850 degrees F, while for the SRC-II material, the 50 degrees F cuts were only obtained between 700 and 850 degrees F. These cuts, as well as the parent material, were tested for their ability to initiate skin tumors by applying a single dose (25 mg) to the shaved backs of Charles River female CD-1 mice. After 2 weeks, the mice received twice weekly applications of 5 micrograms of the promoter, phorbol myristate acetate. Only a few tumors were found for SRC-I fractions boiling below 700 degrees F; tumor-initiating activity increased as the boiling point increased. A similar increase in response with increasing boiling point was seen for the SRC-II cuts. The initiating activities for the parent materials were similar to those observed for their respective 800 to 850 degrees F cuts.