Electrical discharges in humid air at atmospheric pressure (nonthermal quenched plasma) generate longlived chemical species in water that are efficient for microbial decontamination. The major role of nitrites was evidenced together with a synergistic effect of nitrates and H 2 O 2 and matching acidification. Other possible active compounds are considered, e.g., peroxynitrous acid.Nonthermal plasma gases are currently under study as potential alternatives to conventional sterilization techniques in numerous settings (the food industry, hospitals). Atmospheric nonthermal plasmas of the gliding-arc type (Glidarc) (9, 25) were found to be efficient against microorganisms for treatments performed under burning discharge (12,13,22,26), and the inactivation of cells in water could continue after the discharge had been switched off (13). Microbial cells were also killed by contact with water that had first been activated by discharges (and so-called plasma-activated water [PAW]) without being themselves subjected to the plasma plume (14, 15). Studies performed hitherto using Glidarc in the context of microbial decontamination have aimed to test the influence of biological (i.e., population level, planktonic or adherent state [14]) and physical parameters on decontamination efficiency. Little is known of the mechanisms of action, especially when PAW is used.UV radiation, charged particles, and temperature are some of the principal factors governing microbial inactivation under plasma technology (20), but they are not relevant for PAW decontamination because the burning discharge is switched off during treatment. It is likely that reactive-nitrogen-and -oxygen-based species play an important role in the lethal effect of nonequilibrium atmospheric air-based plasma (10,20). DNA, RNA, proteins, and lipids are the principal targets of these oxidants (4, 8). The main radical species present in the Glidarc plasma plume have been identified as ⅐ OH and NO ⅐ when humid air is the working gas (1). These radicals are precursors of other active species in water, such as nitrates, nitrites, and hydrogen peroxide (3), which endow the medium with high and sustainable reactivity. The efficiency of these long-lived chemical species in removing chemical pollutants was yet evidenced (24), but their implication in microbial inactivation by PAW was demonstrated for the first time here. Chemical species are also responsible for acidification (2) which role in the antimicrobial activity was also considered during the present study.PAW was produced by application of Glidarc (5 min) over 20 ml of sterile distilled water. The design of the device and the procedure for gas discharge have been described previously (23) , and 1.6 Ϯ 0.2 mmol liter Ϫ1 nitrites (Griess reagent; VWR, Fontenay-sous-Bois, France). Its pH value was 3.0 Ϯ 0.1. No major change in PAW characteristics was detected 30 min after the treatment (corresponding to the maximum period of disinfection). The contributions of nitrites, nitrates, and H 2 O 2 to the lethal effect of PAW w...

Environmental applications of electric discharges are being considered increasingly more often: they imply the chemical properties of the activated species generated in and by the discharge. An overview of the resulting chemical effects is presented, based on rationalized classification, i.e., acid-base effects, oxidizing properties, complex forming reactions, and radical reactions. The gliding discharge is considered to be a specifically suitable plasma source for the treatment of liquids for pollutant abatement in the scope of sustainable environment, and this justifies an overview of the chemical properties. Special emphasis is devoted to temporal post-discharge reactions (TPDRs), which occur when the target is no longer exposed to the plasma source, and several typical examples are detailed. These recently evidenced TPDRs seem to present some general character. They are the key parameters to estimating the efficiency of a discharge treatment; they also have major technical and economical importance for the application of the plasma treatment to pollutant and/or micro-organism abatement at atmospheric pressure and quasi-ambient temperature.