Historically, exposure to
complex mixtures such as
soot,
coal tar,
mineral oils, and cigarette
smoke has been associated with increased
cancer mortality.
Benzo[a]pyrene (BaP) has been used to predict the carcinogenic potency of mixtures. Two complete carcinogenicity C3H/HEJ mouse skin bioassays were undertaken to determine the effect of low doses of BaP on the carcinogenic potential of mixtures. A
toluene solution containing 0.1% each of five noncarcinogenic
polycyclic aromatic hydrocarbons (PAHs),
anthracene,
chrysene,
pyrene, fluoroanthene, and
phenanthrene, produced
tumors in 23% of the mice with a latent period of 73 weeks. With the addition of a 0.001% BaP to the above
solution, 47% of the mice produced
tumors with a latent period of 66 weeks. In the second study,
coal tar in
toluene, which was determined to contain 0.0006% BaP, produced
tumors in 51% of mice with a latent period of 73 weeks. In both studies the BaP solutions by themselves did not produce
tumors. In a third study, the 9-, 2-, and 3-methylbenz[a]-
anthracene compounds were noncarcinogenic using
toluene as the
solvent. With the substitution of
n-dodecane for
toluene all three compounds produced significant numbers of
tumors. The results indicate that (1) low dose levels of BaP can have an impact on the carcinogenic potential of mixtures, (2) the presence or absence of BaP is not always sufficient to account for the observed potency and the synergistic effects of other substances which might be present, and (3) that certain noncarcinogenic methylbenz[a]
anthracenes can have their carcinogenic potential altered by a change in the
solvent used.