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