Effect of indoor sources on fungal spore concentrations and size distributions

Abstract

In this study, the role of some usual domestic activities as potential sources of fungal spores was examined. The source cathegories studied were: handling of organic material (house plants, firewood, potatoes, mouldy food, baking, hay for a pet), resuspension of spores by cleaning activity (vacuuming, sweeping, bed making) and transport of spores on clothes and pets and by air currents. Airborne spores were sampled using 6-stage impactors (Andersen-sampler) on malt extract agar plates. Most of the activities had an apparent effect on the spore counts. However, during baking, handling of house plants and vacuum cleaning, there were no remarkable changes in the spore concentrations. The geometric mean diameter (d g) of fungal spores ranged 1.7-5.5 μm in different experiments. When the total concentration increased, also the d g value increased. The concentration of the largest sized spores decreased most rapidly after the activity, evidently due to faster gravitational settling. The fungal spore sources in this study, created by short time everyday activities in a house, explain much of the wide variation previously observed in fungal spore levels in indoor air. The size distribution of fungal spores has to be taken into account when designing sampling stategies and making comparisons with recommended values.