Micronuclei in red blood cells of the newt Pleurodeles waltl after treatment with benzo(a)pyrene: dependence on dose, length of exposure, posttreatment time, and uptake of the drug.

Aquatic larvae of the newt Pleurodeles waltl were exposed to different concentrations of benzo(a)pyrene (BaP) for various lengths of time. Frequencies of micronuclei in circulating erythrocytes were determined at different times after termination of the treatment. The incidence of micronuclei in larvae kept for 8 days in BaP-containing water displayed a marked increase with dose up to 0.075 ppm and a more gradual one with higher doses, reaching 158 per 1,000 at 0.75 ppm. The lowest dose at which a significant increase could be discerned was 0.01 ppm. Short periods of exposure, less than 2 days, did not result in a marked increase in micronuclei. Uptake and release was studied with tritiated BaP. Larvae concentrated BaP rapidly, attaining maximal levels after 12 hr. The ratio of radioactivity in larvae to that in an equivalent volume of surrounding water was about 200 independent of the amount of BaP added. Calf serum or bovine serum albumin added to the water lowered this ratio by competing for binding to BaP. Radioactive larvae placed in regularly renewed noncontaminated water lost 99% of the label after 100 hr. It is concluded that pleurodele larvae are a promising model for the detection of genotoxic activity in the aquatic environment.