[Comparison of genetic damage in mice exposed to black carbon and ozone-oxidized black carbon]

To make an assessment on the genotoxicity caused by black carbon (BC) and ozonized black carbon (O₃-BC).

In this study, 74 healthy male ICR mice [weighed (28 ± 1.5) g] were randomly divided into 7 groups, including one phosphate buffer solution (PBS) control group and six particles exposed groups by intratracheal instillation with either BC or O₃-BC at the doses of 50, 100, 200 μg/mouse, respectively. There were 12 mice in the groups of 200 μg/mouse and 10 mice in others. The mice were sacrificed 24 h after four intratrachealinstillations. The activities of catalase (CAT) in serum and the levels of malondialdehyde (MDA) in lung tissue homogenate were measured. As the DNA damage mark, 8-hydroxyguanosine (8-OHdG) in urine and serum were quantified with ELISA method. Micronucleus test was used for potential genotoxicity of BC and O₃-BC. Hematoxylin and eosin staining was used to stain lung paraffin section.

The mice were in good condition during instillation, and the liver coefficient of the test groups was significantly lower than that of the control group (P<0.05). The activities of CAT in serum significantly increased in the 100 μg/mouse and 200 μg/mouse groups after being exposed to these two kinds of particles. The micronucleus rate in allthe BC and O₃-BC exposed groups increased (P<0.05), but there was no statistically significant difference among the groups in the levels of 8-OHdG in serum and urine and MDA in lung tissue homogenate. Inflammatory response was found in the lung tissue under the microscope after exposure to BC and O₃-BC.

Intratracheal instillation of BC and O₃-BC induced increasing of oxidative stress and genetic damage in mice. But there was no significant difference between these two particles in toxicity. Whether the genotoxicity of O₃-BC is higher than that of BC or not is uncertain. Further research is needed.