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Hamsters were chronically exposed to B(a)P by inhalation (IRIS 1992) and
were shown to develop respiratory tract tumors. Those hamsters in the highest
dose group developed upper digestive tract tumors.
USEPA has classified B(a)P as a Group B2, or probable human carcinogen.
The oral cancer slope factor is based on a dietary study in mice.
Toxicokinetics
There are no toxicokinetic data for B(a)P in humans (USEPA 1980). Animal
data indicate that B(a)P is readily absorbed after exposure by inhalation or oral
intake and distributes to many tissues in the body (USEPA 1980). B(a)P in itself
is not believed to be carcinogenic, but metabolized by the cytochrome P-450
dependent mixed function oxidase system, often referred to as the aryl
hydrocarbon hydroxylase (AHH) system. The metabolism results in a more
hydrophilic compound which is easier to excrete, although is carcinogenic. The
hepatic metabolic pathway for B(a)P metabolism is readily inducible by
exposure to a variety of chemicals, including B(a)P, and is found in most
mammalian tissues. It catalyzes the formation of reactive epoxide intermediates
as well as the ultimate carcinogenic form of B(a)P: the B(a)P-7,8-diol-9,10-
epoxide (USEPA 1982) which is capable of forming covalent bonds with cellular
macromolecules such as DNA, RNA, and proteins. This covalent binding and
subsequent alteration of structure and function may result in tumor formation.
Because of their high lipid solubility, PAHs are believed to be distributed
throughout the body. Relative to other tissues, they tend to localize in body fat
and fatty tissues.
Ecological effects
The reader is requested to review the toxicity profile for PAHs for
information regarding ecological effects.
References
Integrated Risk Information System (IRIS) on-line database. (1992).
International Agency for Research on Cancer (IARC). (1973). "Certain
monographs on the evaluation of carcinogenic risk to humans." Polycyclic
aromatic hydrocarbons and heterocyclic compounds. Vol 3. World Health
Organization, Lyon, France.
International Agency for Research on Cancer (IARC). (1983). "IARC
monographs on the evaluation of the carcinogenic risk of chemicals to
humans." Volume 32: Polynuclear aromatic compounds, Part 1, Chemical,
environmental and experimental data. World Health Organization, Lyon,
France.
D17
Appendix D Toxicological Profiles

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