The carcinogenic effect of a series of petroleum-derived oils on the skin of mice.

Six groups of 30 Swiss mice were treated by application to the skin in the dorsolumbar region two times a week for 12 months of a "white oil" and five samples of petroleum oils derived from the same "crude" (Middle East), which were collected in the same refinery at different stages of "solvent treatment" and which form a homogeneous series with increasing concentrations of polyaromatic hydrocarbons (PAH). The macroscopic and histopathologic examination of the animals (skin and organs) up to 18 months shows the following effects with respect to the 60-mouse control group: --a marked irritating effect for the "aromatic extract," the "distillate," and a "mixture" of intermediary concentration between "distillate" and "raffinate," --a definite tumorigenic effect on the skin (papillomas, kerato-acanthomas, squamous cell carcinomas, and fibrosarcomas) of the "aromatic extract" and the "distillate." The biological answer is in significant association with the PAH concentration of the samples, which is estimated by different analytical methods: viscosity index, percentage of aromatic carbon, "total PAH" according to a gravimetric method, and benzo[a]pyrene concentration.