| INTRODUCTION:
The pollution of the atmosphere has been in the public eye for many years. Adverse affects of outdoor air pollution to the environment, natural and manmade structures and to human health has led to the creation of many regulations and to the development of many control technologies. However, only recently has the public become aware of possible hazards involving indoor air pollutants. The EPA estimates that the average American spends as much as 90% of their time indoors. This further escalates the potential for problems associated with exposure to indoor air pollutants. Indoor air pollution is now a popular topic in the United States and provides a growing concern for the health of many individuals.
To conserve energy, modern building construction calls for tightly sealed, wellinsulated structures. Natural ventilation has been sacrificed for energy savings. The use of air conditioning systems in warm seasons is another major contributor toward reduction in natural ventilation among modern buildings. These factors contribute to the build up of contaminants in indoor air, where pollutant concentrations often exceed outdo or levels.
Studies by the EPA Indoor Environments Division indicate that indoor air levels of many pollutants are commonly 2 to 5 times higher than outdoor concentrations. Without air cleaning or air pollution control devices to remove pollutants from outside intake air, a background concentration of all the pollutants found outside will also be found in the air indoors. Pollutant concentrations build up in the indoor environment due to sources emitting inside the st ructure. Sources of indoor air pollutants range from common cigarette smoke to noxious fumes emitted from synthetic building materials. Health problems associated with poor indoor air quality are not solely related to chemical pollutants found indoors but are also linked to biological contaminants deteriorating the qu ality of the air.
Pollen brought in from the outside and molds and bacteria found growing indoors impact human health. Both pollen and mold commonly contribute to allergic respiratory conditions and can cause asthma among atopic individuals. In addition to allergenic effects of inhalation exposure to fungal spores in air, other familiar symptoms that are unrelated to strictly respiratory effects include tiredness and headache. Not only do many types of mold cause allergic reactions, but the spores of many fungi also contain various kinds of toxins. Exposure to mycotoxins in agriculture has been recorded and recognized as harmful for over half a century. Aflatoxin, the most potent carcinogen known, is commonly found in the processing of corn and peanuts contaminated with mold growth. Volatile organic compounds (VOCs) are another by-product of mold metabolism. Various ketones, alcohols and other volatiles have been associated with mold growth. These compounds contribute to the characteristic earthy or musty odors commonly found in damp basements and crawlspaces.
Modern sampling techniques for analysis of fungi in indoor air use particulate samplers to collect airborne fungal spores onto agar media to be identified by their gross morphology and sporing characteristics. The output of this analysis yields a numerical value of colony forming units (CFU)/m3 of air. This method has been criticized as to how accurately it represents the environment from which it is sampling. The spores and mycelia fragments that are collected and grow on the collection media only represent the viable particulates collected. Fungal spores decline in viability from the moment they are produced. Light and desiccation easily damage many spores, yet spores of Aspergillus and Penicillium have been known to survive being in dry air for decades. The number of viable spores of a particular fungus may be undetectable while the total number of spores, non-viable plus viable, can be enough to cause a respiratory problem. Another problem arises between competition of viable particles on the agar media. Some fungi compete poorly with other fungi on the collection plates, or their colonies are not sufficiently distinctive and they go undetected with this sampling method. The total number of fungal particulates in indoor air is not well represented by those that can be collected, identified on agar plates and counted as CFUs. | 
