Two-year skin carcinogenicity studies were conducted in C3H mice to assess the effects of irritation and selected compositional parameters on the carcinogenic potential of four
petroleum liquids. Three samples (lightly refined paraffinic oil, LRPO; lightly hydrodesulfurized specialty oil, LHSO; jet fuel, JF) can be generically classified as middle distillates, i.e. distillation occurs between 350 and 700 degrees F (175-370 degrees C). The fourth sample was a
Steam Cracked Gas Oil (SCGO) that distilled within the same range. In studies that assess the effects of irritation on tumorigenicity, LRPO was tested undiluted or was diluted to 50% and 25% in either
mineral oil (which eliminated irritation of the skin) or
toluene (which did not). Undiluted LRPO elicited
tumors in 8% of the mice. Both dilution procedures eliminated tumorigenic potential. Thus, it was possible to maintain a visible level of skin irritation equivalent to that elicited by undiluted LRPO without inducing
tumors. SCGO elicited a chronic
irritant state grossly equivalent to LRPO but was not tumorigenic.
Jet Fuel A (JF) was tested undiluted using both a standard skin painting protocol and an intermittent dosing schedule in which treatment was suspended periodically to allow skin irritation to resolve. The standard treatment protocol of JF resulted in both marked skin irritation and
tumors in 44% of the mice. However, using the intermittent schedule, the
tumor yield was reduced to 2%. Collectively these data demonstrate that
tumor formation is not a necessary sequelae to chronic skin irritation. Conversely, prevention of a marked chronic
irritant state was accompanied by decreased
tumor yield. These data suggest that the chronic
irritant state may be a necessary but not sufficient condition for
tumor formation. In studies to assess the effects of compositional parameters, a lightly hydrodesulfurized specialty oil (LHSO) similar to LRPO but refined to have negligible levels of
sulfur compounds (3 ppm), elicited chronic
irritant and
tumor responses (10%) similar to LRPO. Thus, the level of
sulfur compounds does not appear to affect the tumorigenic activity for products in this boiling range. The SCGO which did not produce
tumors contained only
aromatic hydrocarbons, a finding consistent with previous reports that aromatics may not be the source of tumorigenic potential in
petroleum fractions boiling between 350 and 700 degrees F (175-370 degrees C).