3. Single cell gel electrophoresis (SCGE) assay
The SCGE, or comet assay, was performed according to the method proposed
by Singh et al. (1988). Human leukocytes were treated with different doses of each
detergent (range 1–2000 mg/L) at 37 1C for 1 h. Negative (distilled water) and
positive (ethyl methanesulfonate, 2 mM) controls were performed. After treatment,
the assay was performed only on samples with viability 470%, according to
the procedure proposed by Tice et al. (2000). After slide preparation and cell lysis,
DNA was subjected to 20-min unwinding and 20-min electrophoresis (pH413,
0.8 V/cm and 300 mA). The slides stained with ethidium bromide were examined
under a fluorescence microscope (Olympus CX 41RF) equipped with a BP 515–
560 nm excitation filter and an LP 580 nm barrier filter. Fifty randomly-selected
cells per slide (two slides per sample) were analysed. The extent of DNA migration
was evaluated by both ‘‘visual score’’ (based on visual classification of DNA
damage) and the comet parameter ‘‘tail intensity’’ (percentage of DNA migration
in the tail) detected using an automatic imaging system (Komet 5, Kinetic Imaging
Ltd). Significance of the effect of each dose against the negative control was
determined using Dunnett’s test.