Single strand DNA breaks in human leukocytes induced by ultrasound in vitro

Single strand breaks (SSBs) in the DNA of fresh human leukocytes were analyzed after in vitro exposure to ultrasound in an ice bath. The alkaline elution method was used to quantify the frequency of SSBs. Five different ultrasonic exposures were employed: (1) 53 mW/cm2 spatial-peak temporal-average intensity (SPTA), 0.37:100 microseconds pulsed 6.2 MHz ultrasound presumably without cavitation, (2) 470 mW/cm2 (SPTA) continuous 1.7 MHz ultrasound with gas-body activation, which is a form of cavitation lacking in chemical activity, (3) 10.8 W/cm2 (SPTA), 3.0:100 microseconds pulsed 1.48 MHz ultrasound, presumably without cavitation, (4) 161 W/cm2 (SPTA) continuous 1.45 MHz ultrasound with transient cavitation, and (5) 94 W/cm2 (SPTA) continuous 8 MHz ultrasound presumably without cavitation. All of these exposures produced negative results, except (4), which yielded a significantly increased frequency of SSBs relative to sham exposed cells. For this condition, the SSB effect was comparable in magnitude to that of 1 Gy of 60Co gamma-rays, and may have resulted from the chemical activity associated with transient cavitation. The SSBs were detected in cells which remained intact after exposure; however, it is uncertain if any of the ultrasonically-induced SSBs occurred in viable cells.