Relationships among DNA adducts, micronuclei, and fitness parameters in Xenopus laevis exposed to benzo[a]pyrene

We investigated whether hepatic DNA adducts, erythrocytic micronuclei, wet weight, developmental stage, wet weight at metamorphosis, and time to metamorphosis changed in larval Xenopus laevis exposed to varied doses of benzo[a]pyrene (B[a]P). Using 32P-postlabeling, we observed relative DNA adduct levels of 0 to 13.7 × 10−7 following continuous exposure to 0 to 496 nM B[a]P for 12 days and relative levels of 0 to 10 × 10−7 after exposure to 248 nM B[a]P over a range of 0 to 16 days. Mean numbers of micronuclei were 1.7, 6.3, and 16.4 1000 red blood cells after exposure to 0, 31, and 248 nM B[a]P, respectively, for 14 days. Micronuclei also ranged from 1.3 to 120.5 1000 red blood cells following exposure to 248 nM B[a]P over a range of 0 to 16 days. Comparatively, levels of both DNA adducts and micronuclei were greatly reduced in animals exposed previously to 31 and 248 nM B[a]P, but assayed at metamorphosis. Larvae exposed to 248 nM B[a]P for 14 days took approximately 4 days longer to metamorphose than unexposed larvae. This increased time to metamorphosis was associated with increased DNA adducts and micronuclei in larvae exposed to 248 nM B[a]P. However, DNA adducts and micronuclei also increased in larvae exposed to 31 nM B[a]P, while time to metamorphosis did not. Larval wet weight was reduced by as much as 44% immediately following exposure to B[a]P. However, there was no effect of exposure on wet weight at metamorphosis. Exposed animals were up to 2 developmental stages younger than unexposed animals in one experiment, but differences among exposed and unexposed animals were less distinct in a second experiment. These studies suggest that DNA adducts and micronuclei can be sensitive measures of sublethal DNA damage, as well as possible short-term indicators of indirect effects on fitness in amphibians.