Potting Medium Microbial Respiration Rates and Sporicidal Efficacy Responses to a Single Application of Three Chlorine Dioxide Formulations

The objectives of this study were to determine the efficacy of ClO₂ applied as a granule or a liquid on microbial respiration in a sphagnum peat moss medium. To determine the efficacy of the ClO₂ treatments, microbial respiration was measured pre and post application of ClO₂ inoculated and un-inoculated media. Two formulations of disinfecting oxidants were used in this study. The first formulation was a proprietary product available as a granule that converts to a gas phase form of ClO₂ when exposed to a bisulfate activator and the second was a proprietary liquid electrobiocide (EB) at 600 ppm ClO₂.  Sphagnum peat moss medium was blended with play sand at 3:1 by volume and then autoclaved at 250 C for 30 min. There were 12 treatment combinations: ClO₂ granules blended with the medium at 1.5 and 3 g per 60 g of medium; ClO₂ sachet treatments at 3, 6, and 9 g per 60 g medium; and three volumes of EB (100, 200, and 300 ml per 60 g medium); and three untreated controls, autoclaved and not autoclaved media. The treated media and controls were then inoculated with Bacillus subtilus (ATCC #19659) spores. The final treatment was one of the three controls, autoclaved medium and not inoculated with B. subtilus.  Respiration rates of the potting media were measured prior to the treatments and then   4, 8, 12, 20,  38, and 60 days after the treatments as CO₂ flux with a soil respiration flux chamber attached to a portable infrared gas analyzer (LI-6400XT, Li-Cor, Inc.). Media samples were collected 64 days after treatment to enumerate the number of viable B. subtilis spores (CFU·g^-1 medium) for each treatment.  Sixty days after treatment, the inoculated control medium had a respiration rate of 2.96 µmol CO₂·m^-2·s^-1.  Sixty days after treatment, the granular ClO₂ formulation had the lowest respiration rate of all treatments at 0.99 µmol CO₂·m^-2·s^-1.   The chlorine dioxide granule treatment resulted in a log₁₀ reduction in viable B. subtilus spores of 28% from the initial spore counts in the liquid suspension.  The respiration rates of the inoculated medium and the sporicidal efficacy results show that two chlorine dioxide formulations can partially control soil-borne microorganisms after one application in sphagnum peat moss based potting medium.