Lymphocyte cultures for chromosomal aberration assay were processed as described earlier . Briefly, cultures were initiated by adding 0.2 mL of phytohemagglutinin into each vial containing 0.5 mL of blood and 4.5 mL of RPMI-1640 supplemented with 7.5% NaHCO3, 20% fetal calf serum, 200 mM L-Glutamine, penicillin (100 units/mL), and streptomycin (100 μg/mL) and incubated at 37°C in 5% CO2. At 46th hour of incubation, the cells were blocked at metaphase by adding colcemid at a final concentration of 0.1 μg/mL and the cultures were further incubated until 48 hrs. The samples were then harvested after hypotonic treatment (20 minutes with 0.45% KCl at 37°C), washed three times with Carnoy's fixative, and cast on clean precooled slides. All slides were stained with 10% Giemsa, air-dried, and mounted with cover-slip using DPX mounting medium to analyze the chromosomal aberrations.