Abstract: To study the effects of benzo(a)pyrene [B(a)P] and chlorophenothane(DDT) exposure alone or in combination on apoptosis of liver cells in mice. METHODS： 66 healthy female Kunming mice were randomly divided into 11 groups： 0.5， 5， 50 mg/(kg·d) B(a)P groups; 0.025， 0.25， 2.5 mg/(kg·d) DDT groups;0.5 mg/(kg·d) B(a)P + 0.025 mg/(kg·d) DDT group; 5 mg/(kg·d) B(a)P + 0.25 mg/(kg·d) DDT group; 50 mg/(kg·d) B(a)P + 2.5 mg/(kg·d) DDT group; blank control group (normal feed) and solvent control group(equal volume of oil). Exposure groups were injected with oil containing B(a)P and DDT once a day. After 21-day intraperitoneal injection， livers were taken for frozen sections. Apoptosis of liver cells was examined by TUNEL method. RESULTS：The apoptotic rates of 5 and 50 mg/(kg·d) B(a)P group were significantly higher than that of the control groups (P<0.01 or P<0.05)， besides the apoptotic rate of the 50 mg/(kg·d) B(a)P group was higher than that of the 0.5 and 5 mg/(kg·d) B(a)P groups (P<0.05). The apoptotic rates of the DDT groups had no significant difference with the control groups (P>0.05). In the combined exposure groups， apoptosis was more serious than that of the control groups (P<0.01)， while the comparison between the combined exposure groups showed no statistical difference(P > 0.05)， same with the combined groups and the corresponding B(a)P groups(P > 0.05). CONCLUSION：In these experimental conditions， 5 and 50 mg/(kg·d) B(a)P groups could cause liver cell apoptosis， and the higher the dose of B(a)P， the higher the apoptotic rate. No apoptosis could be demonstrated in 0.025， 0.25， 2.5 mg/(kg·d) DDT groups. All of the combined exposure groups could cause liver apoptosis， but there was no clear dose-response relationship observed. Above all， either B(a)P exposure alone or combined with DDT could cause liver cell apoptosis in mice. Whether it could cause other toxicological effects would be discussed in the future.

Key words: benzo(a)pyrene, chlorophenothane, combined exposure, apoptosis of liver cells