As drinking water supplement: 0.5 g or 1 g mixed with 99.5 or 99 mL distilled water for 3 days.

Thus, 6 h incubation was applied for this study. Stock solution of SEC (S-ETHYLCYSTEINE) was prepared, and used for further dilution by bronchial epithelial growth medium (BEGM). BEAS- 2B cells were routinely cultured in BEGM, treated by 2.5 mM l-glutamine, 10% fetal calf serum, 100 units/mL streptomycin, and 100 units/mL penicillin (pH 7.4) under 95% air and 5% CO2 at 37 °C. Culture medium was changed every 72 h, and cells were subcultured every 7 d. Phosphate buffer saline (PBS, pH 7.2) was added to adjust cell number to 105/mL for experiments and analyses. After aspiration, cells were incubated with S-ETHYLCYSTEINE at 4, 8, or 16 μmol/L at 37 °C for 6-h, which caused 96.4 ± 1.2% incorporation of target compound into BEAS-2B cells. Cells were further treated by 100 μMH2O2 at 37 °C for 4 h