Fig. 1.

(a) Cell viability in human bronchial epithelia cells treated with 4, 8, 16, 32, and 64 μmol/l benzo(a)pyrene (BaP) for 12, 24, and 48 h. (b) Cell viability in human bronchial epithelia cells treated with 0, 50, 100, 250, and 500 nmol/l folic acid for 12, 24, and 48 h. (c) Cell viability in human bronchial epithelia cells pretreated with 50, 100, 250, and 500 nmol/l folic acid and exposed to 32 μmol/l BaP for 12, 24, and 48 h. Data represent the mean±standard error values of three independent experiments. Compared with the positive control group, and **P<0.01, compared with the negative control group, ^#P<0.05 and ^##P<0.01.