Comparison of the effects of arsenic and cadmium on benzo( a)pyrene-induced micronuclei in mouse bone-marrow

Abstract

This study was undertaken to investigate the genotoxic interactions between the common environmental pollutants: arsenic (As), cadmium (Cd) and benzo( a)pyrene (BaP), which are known to be human carcinogens. C57BL/6J/Han mice were pre-treated with 100 mg cadmium chloride (Cd 2+)/L or 50 mg sodium arsenite (As 3+)/L in drinking water for 7 days and then given a single dose of 200 mg BaP/kg bw by intra-peritoneal injection. A third group of mice did not receive the pre-treatment and was given BaP alone. Mice were sacrificed before or at 12, 24, 48 or 72 h after BaP administration. Chromosome damage in bone-marrow cells was assessed by use of the micronucleus test. The study revealed that BaP induced a statistically significant increase in micronucleus (MN) frequency at 48 h after administration. In animals exposed to Cd in drinking water no enhancement of genotoxicity was observed compared with the control group that was given tap water only. In Cd/BaP co-exposed animals, the MN frequency at respective time points did not differ from that for the animals exposed solely to BaP. A statistically higher MN frequency was found in bone marrow of animals exposed to As compared with controls that received tap water (0.92 ± 0.29% versus 0.38 ± 0.13%, respectively). This effect was even more pronounced after combined exposure to As and BaP. In the co-exposed animals, significantly elevated levels of MN were detected in samples examined at 12, 24 and 48 h after BaP administration, compared with animals receiving BaP alone (1.14 ± 0.31%, 1.26 ± 0.3% and 2.02 ± 0.45% versus 0.44 ± 0.13%, 0.44 ± 0.11% and 1.04 ± 0.44%, respectively). These findings imply strong interactions between As and BaP, but not between Cd and BaP, in inducing DNA damage in polychromatic erythrocytes in mouse bone-marrow.