The effect of ozone on common environmental fungi.

OBJECTIVE To determine if gaseous ozone can effectively kill common environmental fungi. DESIGN This study was designed to test the null hypothesis that there is no significant difference in viability between fungal conidia treated with ozone and fungal conidia not treated with ozone. A single control group design was utilized. SETTING Academic research laboratory. INTERVENTIONS Freshly prepared suspensions of Cladosporium spp., Stachybotrys spp., and Aspergillus niger conidia were diluted and plated onto the surface of solid agar plates. The plates were exposed to room air or to different concentrations of ozone for up to four hours, as were uninoculated plates. All plates were then incubated at 25 degrees C until quantitative colony counts could be performed. MAIN OUTCOME MEASURE The effect of ozone on fungal conidia viability was assessed by comparing quantitative colony counts from conidia exposed to ozone to quantitative colony counts from conidia exposed only to room air. RESULTS There was a significant (p < 0.05) decrease in viable conidia of all three fungi, at ozone concentrations of 5.0-12.8 parts per million, by four hours of exposure. However, in every case, some conidia remained viable even at the highest level of exposure. CONCLUSIONS These data suggest that ozone must be used in conjunction with other methods of remediation or for more prolonged exposure times in order to eliminate fungal contamination of buildings.