Investigation into ethylene oxide treatment and residuals on DNA and downstream DNA analysis

- Ethylene oxide is an effective post-production treatment on cotton and rayon swabs.
- After 3 weeks post EO treatment, residual levels were below measurable levels.
- Rayon swabs retained less EO than cotton swabs.
- There was a negligible effect of EO treatment on DNA recovered from rayon swabs.
- Cotton swabs should not be used until 5 weeks post EO treatment.

Recent years have seen a significant increase in the sensitivity of DNA testing, enabling the determination of DNA profiles from low levels of cellular material. However, the increased sensitivity is in many ways a double-edged sword as background contaminating DNA generated during the manufacture of consumables and sampling devices is now being detected and may compromise the interpretation of the DNA profile results. This study initially demonstrated the effectiveness of ethylene oxide (EO) as a post-production treatment to eliminate DNA on swabs, used as a sampling device for the recovery of cellular material. Subsequently, the potential adverse effects of any residual EO remaining on the swabs on the downstream DNA analysis on both rayon and cotton swabs were investigated and the levels of remaining EO measured. Two main variables were tested: the amount of time elapsed since EO treatment of the swabs prior to use, and the time elapsed between cellular material collection and DNA analysis. Residual levels of EO were found to be below quantitation levels and therefore also international standards. The results indicated that while there was a negligible effect of EO treatment on DNA recovered from rayon swabs, there was however an adverse effect on the DNA profiles recovered from cotton swabs. The adverse effect was negatively correlated with time since EO treatment and positively correlated with time to DNA analysis.