CHRONIC DERMAL STUDIES OF PETROLEUM STREAMS IN MICE

During petroleum refining, a large number of products are generated wh ich have varying chemical and physical properties. These are known in the industry as petroleum streams. In order to characterize their carc inogenic activity, a number of these commercially produced streams wer e administered to C3H/HeJ mice in chronic dermal bioassays. The bioass ays were conducted using one of two study designs: the first set of te st materials was applied for a lifetime and the second set for 24 mont hs. In the lifetime study, the last mice in the test groups survived f or periods of 31 to 32 months. Middle distillates, boiling in the rang e 115-390 degrees C, were found to decrease the lifespan of exposed mi ce compared to controls or streams of higher and lower boiling ranges. These middle distillate streams included straight run kerosine, hydro desulfurized middle distillate, straight run middle distillate, light catalytic cracked distillate, and 90/10% and 70/30% mixtures of the la st two. The middle distillate streams also proved to be active as carc inogens, with tumor incidence ranging from 16 to 67%. Light alkylate n aphtha, heavy catalytic reformed naphtha, vacuum residuum, and unleade d gasoline did not demonstrate significant carcinogenic potency. Heavy thermal cracked naphtha, heavy catalytic cracked naphtha, and hydrotr eated light naphthenic distillate were dermal carcinogens of low poten cy in this study. Administration of light catalytic cracked naphtha le d to a low incidence of very late developing tumors with a mean latenc y of 118 weeks. Application of the 0.1% solution of catalytic cracked clarified oil in toluene did not result in a significant incidence of tumors, but the 10% solution caused almost 100% mortality and 100% tum or incidence in 12 months. There was no correlation between carcinogen ic potency and the indices of irritation, alopecia, erythema, and scab bing. Only two of the streams tested, hydrotreated light naphthenic di stillate and 10% catalytic cracked clarified oil, contain polynuclear aromatic hydrocarbons (PNAs) and may be presumed to be complete carcin ogens. The middle distillates and heavy naphthas are nonmutagenic and essentially free of PNAs. Their activity may result from promotion of already-initiated skin sites. Where comparisons could be made, reducin g the exposure period from a lifetime (29-32 months) to 24 months did not change the evaluations of stream carcinogenicity except in the cas e of light catalytic cracked naphtha where six of the seven mice that developed tumors did so after 24 months. (C) 1996 Society of Toxicolog y