SCE increases after an accidental acute inhalation exposure to EtO and recovery to normal after 2 years.

Sister-chromatid exchanges (SCEs) were studied in 3 workers accidentally exposed for about half an hour to high levels of ethylene oxide (more than 700 ppm) during a sterilizing process. The 3 workers had clinical symptoms of exposure and were tested for SCE frequencies 5 days and 2 years after the accident: 2 had also been tested 6 months earlier. All 3 showed a similar increase in SCEs after the accident, to a mean of 13.8 SCEs/cell compared with 8.6 for a control group. The incidence of 'high-frequency cells' was markedly elevated but decreased over 2 years, when the mean SCE frequencies had also returned to pre-accident levels.