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This was rounded to a PEF of 0.1.
11. Dibenz[a,h]acridine. Dibenz[a,h]acridine was also assigned a PEF of 0.1. Its carcinogenic
classification by IARC was based on studies published in 1940 and earlier and the studies did not
appear appropriate for estimation of a PEF. Since its structure is similar to dibenz[a,j]acridine, it was
assigned the same PEF as dibenz[a,j]acridine until usable compound-specific bioassay data becomes
available.
12. 7H-Dibenzo[c,g]carbazole. 7H-dibenzo[c,g]carbazole was assigned a PEF of 1.0. Warshawsky
et al. (1992) compared the tumor-initiating ability of 7H-dibenzo[c,g]carbazole to BaP in mouse skin.
Two hundred nanomoles of each compound were applied to 30 mice, then promoted with a phorbol
ester for 24 weeks. Twenty-seven out of 30 BaP-treated mice (90%) had skin papillomas, while 26 of
30 (87%) of the dibenzo[a,j]acridine-treated mice had skin papillomas for a relative tumorigenic activity
of 0.97. This was rounded to a PEF of 1.
13. Dibenzo[a,l]pyrene. Dibenzo[a,l]pyrene was assigned a PEF of 10. Cavalieri et al. (1989; 1991)
studied the tumor-initiating and dose-response tumorigenicity of dibenzo[a,l]pyrene in mouse skin and
rat mammary gland. BaP was used as a reference compound in some experiments. Dibenzo[a,l]pyrene
was the most potent member of the group. Several levels of PAHs were tested. When results from
33.3 nanomoles of dibenzo[a,l]pyrene as a skin tumor initiator (with promotion by a phorbol ester)
were compared to results using the same amount of BaP, dibenzo[a,l]pyrene induced skin tumors in
23/24 (96%) of the animals while BaP induced tumors in 10/23 (43%) which resulted in a relative
potency of 5.8. Dibenzo[a,l]pyrene induced approximately 5 times as many tumors per tumor-bearing
animal. In a second experiment 4 nanomoles of each chemical were compared. Ninety-two percent
(22/24) of the dibenzo[a,l]pyrene-treated mice had tumors but only 4% (1/24) of the BaP animals,
which yielded a relative potency of 25.1. In a third experiment 100 nM were compared without
promotion. Twenty-nine percent (7/24) of the dibenzo[a,l]pyrene-treated mice had tumors but only 4%
(1/24) of the BaP animals, for a relative potency of 4. Finally, with direct application to the mammary
gland, 0.25 and 1.0 nanomoles dibenzo[a,l]pyrene led to tumors in all the rats treated (19 and 20 per
group, respectively) whereas only one animal in the 0.25 micromoles BaP group showed a tumor for a
relative potency greater than 100. Based on its much greater tumorigenic activity than BaP in the above
tests, dibenzo[a,l]pyrene was assigned a PEF of 10.
14. Dibenzo[a,h]pyrene. Dibenzo[a,h]pyrene was assigned a PEF of 10 since, in the experiments by
Cavalieri et al. (1989) in which all four dibenzo[a]pyrenes were studied, its tumor causing activity was
similar to dibenzo[a,l]pyrene. For example, when used to initiate tumors in mouse skin, 18 of 24 (75%)
of mice treated with dibenzo[a,h]pyrene had tumors compared to 22 of 24 (92%) with dibenzo
[a,l]pyrene. Controls showed skin tumors in 2 of 23 mice (9%).
15. Dibenzo[a,i]pyrene. Dibenzo[a,i] pyrene was assigned a PEF of 10 since, in the experiments by
Cavalieri et al. (1989) in which all four dibenzo[a]pyrenes were studied, its tumor-causing activity was
similar to dibenzo[a,l]pyrene. For example, when used to initiate tumors in mouse skin, 15 of 24 (63%)
of mice treated with dibenzo[a,i]pyrene had tumors compared to 22 of 24 (92%) with dibenzo-
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