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Bioaerosols are organisms or biological agents which can be dispersed through the air and affect human health. These bioaerosols can contain bacteria, fungi, actinomycetes, arthropods, endotoxin, microbial enzymes, glucans and mycotoxins (Millner, 1994). During composting, bioaerosols are not only present in waste materials but also can be generated. These bioaerosols can affect the health of workers or residents adjacent to composting facilities. The level of bioaerosols or the type could be a function of the feedstock. Level of bioaerosols in the atmosphere of a facility or in the air surrounding a facility also can be a function of facility design and operations.
The bioaerosols discussed are Aspergillus fumigatus and endotoxin since these have been shown to be in composting facilities at significant levels which could affect worker health or the public surrounding facilities. Other potential biological agents that could present health problems are the thermophilic actinomycetes, glucans and mycotoxins. However, these bioaerosols have not been shown to be of significant importance or prevalent in significant quantities in composting operations.
ASPERGILLUS FUMIGATUS
Aspergillus fumigatus is a member of the genus Aspergillus which includes approximately 300 species that are very common in the environment (Rippon, 1974; Slavin and Winzenburger, 1977; Emmons et al., 1977). It is a common fungus found in decaying organic matter and soil throughout the world (Rippon, 1974). As Rippon (1974) indicates, "Aspergillus spores are airborne and constantly inhaled." Furthermore, he states, "the omnipresence and ubiquity of Aspergillus organisms are a major factor in designating this planet as 'our moldy earth'." Aspergillus fumigatus is heat tolerant and thus survives the high temperatures normally found in composting.
Aspergillus fumigatus belongs to the plant kingdom, Thallophyta phylum, Ascomycetes class, Aspergillales order, and Aspergillaceae family. Aspergillus fumigatus colonies are velvety to floccose, blue-green to gray-green with development of the conidial heads, reverse colorless or showing yellow, green, or red-brown shades. Conidial heads are columnar up to 400 x 50 microns, but often much shorter or smaller. Conidiophores are smooth and short, often greenish, arising from submerged hyphae or as very short branches from aerial hyphae. These enlarge gradually upwards to form the apical flask shaped vesicle (Commonwealth Mycological Institute, 1966).
OCCURRENCE IN THE ENVIRONMENT
Aspergillus fumigatus has been found to grow on numerous substrates and media. The...