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from an inhalation exposure study (Thyssen et al., 1981) has been developed, along with Potency
Equivalency Factors (PEFs) for several related PAHs. (OEHHA, 1993).
Thyssen et al. (1981) exposed male Syrian golden hamsters (24/group) by inhalation to 0. 2.2, 9.5 or
46.5 mg BaP/m 3 in a sodium chloride aerosol (greater than 99% of the particle diameters were between
0.2 and 0.5 µm). The hamsters were exposed to BaP daily for 4.5 hours/day for the first 10 weeks of
exposure; subsequent exposure was daily for 3 hours/day. Total treatment duration was 95 weeks.
Animals dying in the first year of the study were replaced. The effective number of animals in the
control, 2.2, 9.5 and 46.5 mg/m 3 exposure groups were 27, 27, 26 and 25, respectively. Survival time
for the 46.5 mg/m 3 exposure group was significantly reduced (60 weeks) when compared to controls
(96 weeks). Survival times for the other exposure groups were similar to controls. Respiratory tract
(including nasal cavity, larynx and trachea) tumor incidence was significantly increased in a dosedependent
manner in the 9.5 and 46.5 mg/m 3 exposure groups (34.6% and 52%, respectively,
compared to controls); those exposure groups also demonstrated an increase in upper digestive tract
(including pharynx, esophagus and forestomach) tumor incidence (27% and 56%, respectively). This
study was selected as the basis of a cancer potency factor for exposure to BaP by inhalation because it
used the most sensitive species and sex demonstrating a dose response and using the most relevant
exposure route.
Methodology
A linearized multistage procedure (GLOBAL86) (Howe and van Landingham, 1986) was used with the
Syrian golden hamster respiratory tract tumor incidence data of Thyssen et al. (1981) to calculate a
cancer potency factor. Data from the highest exposure group (46.5 mg/m 3 ) was not used due to the
shortened lifespan of the hamsters in this group. Administered dose for the 2.2 and 9.5 mg/m 3 exposure
groups based on an inspiration rate of 0.063 m 3 /day and a body weight of 0.1 kg was 0.152 and 0.655
mg/kg/day, respectively. Surface area scaling was then used to extrapolate a human cancer potency
factor and an inhalation unit risk factor (using assumptions of 70 kg body weight and 20 m 3 /day
inspiration rate). Creosote is approximately 91% PAH, nitro-PAH or hydroxy-PAH (Wright et al.,
1985); a unit risk for creosote can be calculated using the unit risk value for BaP and the PEFs for
related PAHs (OEHHA, 1993).
V. REFERENCES
Agency for Toxic Substances and Disease Registry 1990. Toxicological Profile for Creosote. U.S.
Department of Health & Human Services, Public Health Service, Publication No. TP-90-09.
Axelson O and Kling H. 1983. Mortality among wood preservers with creosote exposure. In: 32nd
Nordic Occupational Hygiene Conference, Solna, Arbetarskyddsstyrelsen, National Board of
Occupational Safety and Health, pp. 125-126.
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