Toxicity and EROD-inducing potency of 24 polycyclic aromatic hydrocarbons (PAHs) in chick embryos

The toxicities (embryolethality) of 24 polycyclic aromatic hydrocarbons (PAHs) were determined in chick embryos using a 72-h test. The substances, dissolved in peanut oil, were injected into the air sacs of eggs preincubated for 7 days. LD₅₀ values were determined for the four most toxic of the 24 compounds. Benzo [k] fluoranthene proved to be the most potent, with an LD₅₀ of 14 g (56 nmol)/kg egg. Dibenz[a,h]anthracene, benz[a]anthracene and benzo[b]naphtho[2,3-d]thiophene were a few times less toxic [LD₅₀=39 g (140 nmol)/kg, 79 g (349 nmol)/kg and 82 g (350 nmol)/kg, respectively]. The LD₅₀ of benzo [k] fluoranthene was only about 5 times higher than that previously found for the most potent coplanar polychlorinated biphenyl (PCB), 3,3,4,4,5-pentachlorobiphenyl [LD₅₀=3.1 g (9.4 nmol)/kg], in the same kind of test. The toxicities of 18 of the PAHs in this study have also been evaluated previously using a 2-week test in chick embryos. Dibenz[a,h]anthracene, which had not been studied earlier in the 2-week test, proved to be almost as toxic as previously found for benzo [k] fluoranthene in that test. Several of the PAHs studied induced EROD activity in chick embryos, and, in general, the most toxic PAHs were also the most potent inducers of EROD. The highest enzyme activities were found after treatment with indeno[1,2,3-c,d]pyrene (12 times the control value) and dibenz[a,h]anthracene (8 times the control value). However, due to the high toxicity of dibenz[a,h]anthracene, the dose used was 7 times lower than that of indeno [1,2,3-c,d]pyrene. Following injection of PAHs on day 7, the EROD activities on day 10 were considerably lower than those obtained after a corresponding treatment with coplanar PCBs in an earlier study. Of the PAHs studied, some exhibited very high embryotoxicity. The most toxic PAHs induced EROD activity, suggesting that their toxicity was at least partly mediated via binding to the Ah receptor.