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Background levels of fungi in NYC - white paper

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1 Background Concentrations of Culturable Fungi in Commercial Office Buildings in the New York City Region By Jack Springston, CIH, CSP, FAIHA INTRODUCTION Bioaerosols, including fungi, are ubiquitous in the indoor and outdoor environment. The growth and dissemination of these organisms is largely dependent upon available growth substrates, moisture, climate, season and human activities. Although normal building materials and furnishings provide ample nutrition for many species of molds, they can only grow and amplify indoors when there is a sufficient supply of moisture. ( 1 ) Mold spores are introduced to the indoor environment from the outdoors in a variety of ways, including ventilation system outdoor air intakes; open doorways and windows; on clothing, footwear, and pets; or even by simply attaching to dust particles. (2,3,4) The primary factors that prevent penetration of outdoor bioaerosols into buildings are physical barriers such as lack of openings, closed or inoperable windows, and filtration. (5) Outdoor air is typically the predominant source of indoor fungi and, in certain situations, may be the source of all indoor fungi. ( 6 ) One study found that approximately 90 percent of the indoor fungi were associated with biodeterioration of plants and may have originated outdoors. ( 7 ) In general, the fungal population and diversity of the indoor air is a function of the amount of outdoor air that has been used to ventilate the building. (8) Although fungal spores can also be introduced into the indoor environment through small cracks and holes in the building envelope, only a fraction of the spores actually penetrate into the indoor air, with the remainder being deposited on the surfaces of the leaks. ( 9 ) For larger sized penetrations, however, spore and particle removal during infiltration is insignificant. ( 10 ) Studies have shown that well maintained heating, ventilation, and air conditioning (HVAC) systems can reduce the total airborne fungi counts indoors by up to or more than 50% as compared with the outdoor air concentrations. ( 11 , 12 , 13 ) Unless there is some indoor source for specific bioaerosols, indoor air levels will generally be lower than those found outdoors, particularly in mechanically ventilated buildings. (14) As a general rule, therefore, the indoor air in dry buildings, in which there is no readily identifiable water intrusion problems, should contain a mixture of phylloplane, or leaf-derived fungi (i.e., Cladosporium, Alternaria and Epicoccum), which are normally present in the outdoor air. (15,16)

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