Sources of indoor fungi in non-problem buildings and dwellings

Abstract

Recent concern over the potential health effects of airborne fungi in buildings has lead to an urgent need for regulating bodies to establish guidelines and standards for indoor fungi. However, indoor fungi have been described based on our knowledge of "outdoor'' fungal ecology and there is a lack of basic understanding of fungal ecology in indoor environments. To date, most of the data on indoor fungi comes from buildings with moisture damage or mould infestation problems and there is a lack of data on fungi occurring in non-problem buildings. The limited number of studies on non-problem buildings suggests that the species range is different and the numbers of fungi are normally very low compared to problem buildings. However, where there is an alteration of the species mixture compared to the outdoor air, and this is due to fungi growing and reproducing indoors, then this may represent an unknown but important health risk from exposure to fungi. The main hypothesis tested in this thesis is that the fungi in the indoor air in nonproblem and well maintained buildings with no history of water damage and no occupant complaints, are sourced from fungi growing outdoors. A second hypothesis was that where indoor airborne fungi in non-problem buildings are not sourced from the outdoors, then they are from internal sources of fungal growth. The best available methods from the fields of aerobiology, microbiology, food & soil mycology, and some novel techniques were used for sampling fungi. Techniques and equipment used included the six-stage Andersen sampler for airborne samples, a Kirby vacuum cleaner for extracting dust samples, an Airotester unit for testing filter material in situ, both normal light and fluorescence microscopy, and both direct and dilution plating for analysing dust samples. Samples were collected only from non-problem indoor environments, which had no records or low levels of complaints or problems and that had no water or moisture damage. The results determined sources of fungi in non-problem buildings and provided direct evidence that fungi are able to grow on air filtration materials and interior furnishings that are kept in good order. In particular, the fungi in indoor air of the healthy buildings were found to be sourced from a mixture of indoor and outdoor sources. Despite the fact that the IAQ and SBS parameters, and the lack of complaints, moisture damage or visible mould all characterised the buildings in this study as healthy or non-problem, the buildings had indoor fungal problems according to the guidelines given in the mycological literature. The HVAC systems investigated were shown to generally reduced the prevalence or eliminated typical outdoor air fungi. However, this filtration effect was shown to be a complex pattern of changes in species mixture at each of the HVAC systems components. Some species reached their highest numbers in the indoor air. The fungal species range isolated from air filtration media was shown to be significantly affected by the type of filter material. The new multi layered polymer filtration media was shown to initially reduced the ability of fungi to grow on the media. This was most likely due to its ability to disperse nutrients and fungi spatially and by having lower water content and pH value. There were indications that the survival of fungi beyond their initial capture may be very brief due to the aggressive environment on the filters. The study provided direct evidence that fungi were able to grow in interior sources such as carpets and furnishings that were kept in dry condition (in non-problem buildings). Each of the different furnishing types were shown to provide a different habitat for fungal growth. The microbial activity of fungi in the furnishings was the same level as reported in several productive soil types. The growth rate and the relative absence of xerophilic fungi indicate that either moist conditions must have existed in the furnishings (despite their good condition) or that the mesophilic fungi had adapted and used a stress tolerant strategy to surviving under the environmental conditions in the furniture. The study concluded that no single study, including this study, has adequately characterised the source(s) of indoor fungi in non-problem buildings. This is due to a lack of understanding that the indoors is a separate and unique ecosystem, which is exacerbated by our lack of basic knowledge about indoor ecosystems. Improving this basic knowledge would require examining the interrelationships among organisms, all aspects of their environment, the flow of energy and substances, and the cycling of nutrients that occurs indoors. The implications of this study suggest that further information on the sources of fungi in non-problem buildings needs to be collected. The next step in research will be to adopt the approach of describing the indoor environment as a separate and functioning ecosystem. This would include investigating the proportion, diversity, different types and species of organisms; the interrelationships among organisms and between organisms and their environment. Fundamental concepts that need to be examined include the flow of energy via food-chains and food-webs and the cycling of nutrients biochemically. The results of this study have serious implications for our ecological understanding and for ensuring the health of people who use and occupy indoor environments, especially considering the toxic, allergenic and pathogenic potential of many of the fungi that are commonly occur indoors