The objectives of this dissertation are 1) to quantify indoor-to-outdoor (I/O) ratios of bioaerosols including actinomycetes, fungi, and pollen in single family homes using the microscopic spore counts of filter samples, 2) to investigate the relationship between indoor and outdoor (1→3)-β-D-glucan concentrations as well as to compare the I/O ratio obtained based on (1→3)-β-D-glucan analysis to that obtained from microscopic counts for fungal spores and pollen grains for the overall human exposure to bioaerosols, and 3) to characterize the culturability (the ratio of the culturable concentration of airborne fungi to total fungal spore concentration) for indoor and outdoor airborne fungi.
Air samples were collected for 24 hours with a Button™ Personal Inhalable Aerosol sampler inside and outside of eleven homes located in the Cincinnati, Ohio area. Measurements were conducted over five consecutive days at each home. The selected homes were free of visible mold growth. The sampling period was between Spring 2004 and Fall 2005. Three different analysis methods were utilized in order to quantify the indoor and outdoor level of (1→3)-β-D-glucan, actinomycetes, culturable fungi, pollen, and total fungal spores (i.e., culturable analysis for actinomycetes and culturable fungi, microscopic counting for total fungal spores and pollen, and the kinetic chromogenic Limulus Amebocyte Lysate (LAL) method for the (1→3)-β-D-glucan concentration).
The data for the first and second objective regarding the relationship between indoor and outdoor bioaerosols were obtained by conducting two studies. The first study found that the indoor concentration of fungal spores and pollen followed their outdoor concentrations while indoor levels were mostly lower than the outdoor ones. The I/O ratio of total fungal spores (median=0.35) in six homes was greater than that of pollen grains (median=0.03). The low I/O ratios obtained for pollen during the peak ambient pollination season (spring) suggest that only a small fraction penetrated from the outdoor to the indoor environments. This is attributed to the larger size of pollen grains in comparison to other bioaerosols. Higher indoor concentration levels and variability in the I/O ratio observed for airborne fungi may be associated with indoor sources and/or higher outdoor-to-indoor penetration of fungal spores compared to pollen grains. The concentration of culturable actinomycetes was mostly below the detection limit. The median indoor/outdoor ratio (I/O) for actinomycetes was 2.86.
The second study demonstrated that the I/O ratio of (1→3)-β-D-glucan concentration was marginally greater than that calculated based on the combined number concentration of fungal spores and pollen. This suggests that (1→3)-β-D-glucan data are affected not only by intact spores and pollen grains but also by the airborne fragments of fungi, pollen, and plant material, which are not accounted for by traditional enumeration methodologies. Since the (1→3)-β-D-glucan level may elucidate the total exposure to fungal spores, pollen, and fungal fragments, its I/O ratio may be used as a risk marker for mold and pollen exposure in indoor environments.
The third objective was to investigate the culturability of airborne fungi. The indoor and outdoor concentrations of culturable and total fungal spores were found to significantly correlate. The indoor and outdoor median culturabilities of fungi were 55% and 25%, respectively. Among the seasons, the highest indoor and outdoor culturability of fungi was observed in the fall. Among predominant genera of fungi Cladosporium had the highest median value of culturability (38% and 33% for indoor and outdoor, respectively) followed by Aspergillus/Penicillium (9% and 2%). Increased culturability of fungi inside the homes may have important implications because of the potential increase of allergens from viable spores and the possible pathogenicity of viable fungi for immunocompromised individuals.
This dissertation estimated the relationship between indoor and outdoor concentrations of different types of bioaerosols using long-term sampling methods in the inhalable particle size range. It also gave insight on the indoor and outdoor culturability of airborne fungi. Long-term sampling was utilized, which allowed the collection of more representative data to elucidate human exposure to bioaerosols. Furthermore, culturable and total spore counts were determined by utilizing the same samplers and filter types for indoor and outdoor sampling. This ensures the comparability of indoor and outdoor sampling results since different samples and types of filters as known to collect different types of bioaerosols with different efficiency. This dissertation is a first attempt to characterize the relationship between indoor and outdoor concentrations of airborne (1→3)-β-D-glucan. The comparison of I/O ratios for (1→3)-β-D-glucan versus fungal spore and pollen concentrations provides valuable information on the origin of (1→3)-β-D-glucan in indoor air.