The Application of a Low-temperature Physical Plasma Device Operating Under Atmospheric Pressure Leads to the Production of Toxic NO2

Abstract

Background: Physical plasma is a mixture of reactive particles and electromagnetic radiation. Due to the antimicrobial, immunomodulatory, anti-inflammatory, wound-healing promoting, and antineoplastic effects of body tempered physical plasma under atmospheric pressure (cold atmospheric plasma: CAP), CAP therapy is increasingly becoming the focus of surgical and oncological disciplines. However, when applied in practice, a potential emission of harmful noxae such as toxic nitrogen oxides must be taken into account, which was investigated in the following study.

Materials and methods: MiniJet-R Ar CAP device was characterized with respect to NO_X-specific spectra, ultraviolet radiation C (UVC) intensity in the range of 200-275 nm and the formation of NO_X gases. Instrument-specific parameters such as gas flow, energy setting of the high-frequency generator, and flow rate of the carrier gas Ar were varied. To test the toxic properties of the NO₂ concentrations formed by CAP, SK-OV-3 human ovarian cancer cells were incubated with different NO₂ concentrations and cell growth was monitored for 120 h.

Results: The operation of MiniJet-R led to the formation of NO₂ in the proximity of the CAP effluent. Synthesis of NO led to a NO-specific spectrum in the range of 100-275 nm, whereby UVC radiation produced reached intensities of up to 90 mW/m² NO gas itself, however, was not detectable, as it was converted to NO₂ rapidly. Cell culture incubation experiments demonstrated that NO₂ in these concentration ranges had no influence on the cell growth of human cancer cells.

Conclusion: Although no limit values were exceeded in the present study, the emission of high-energy UVC radiation and toxic NO₂ is a risk factor with regard to the legal regulations on workplace protection (operator hazard) and the approval of medical devices (patient hazard). This is important for considerations regarding treatment frequency and duration. The growth inhibitory effect of CAP treatment on human cancer cells principally suggests a medical application of the MiniJet-R device, although more extensive studies will have to follow.

Keywords: Physical plasma; cold atmospheric plasma; nitrogen oxides; occupational health and safety; plasma medicine; radiation.