Annals of Occupational Hygiene Advance Access originally published online on July 20, 2009
Annals of Occupational Hygiene 2009 53(7):749-757; doi:10.1093/annhyg/mep045
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EDITOR'S CHOICE
Airborne Fungal and Bacterial Components in PM1 Dust from Biofuel Plants
1 The National Research Centre for the Working Environment, Lersø Parkallé 105, 2100 Copenhagen Ø, Denmark
2 Department of Environmental and Occupational Medicine, School of Public Health, University of Århus, 8000 Århus, Denmark
* Author to whom correspondence should be addressed. Tel: +0045-39165242; fax: +0045-39165201; e-mail: amm{at}nrcwe.dk
Fungi grown in pure cultures produce DNA- or RNA-containing particles smaller than spore size (<1.5 µm). High exposures to fungi and bacteria are observed at biofuel plants. Airborne cultivable bacteria are often described to be present in clusters or associated with larger particles with an aerodynamic diameter (dae) of 2–8 µm. In this study, we investigate whether airborne fungal components smaller than spore size are present in bioaerosols in working areas at biofuel plants. Furthermore, we measure the exposure to bacteria and fungal components in airborne particulate matter (PM) with a D50 of 1 µm (called PM1 dust). PM1 was sampled using Triplex cyclones at a working area at 14 Danish biofuel plants. Millipore cassettes were used to sample ‘total dust’. The PM1 particles (29 samples) were analysed for content of 11 different components and the total dust was analysed for cultivable fungi, N-acetyl-β-D-glucosaminidase (NAGase), and (1 
3)-β-D-glucans. In the 29 PM1 samples, cultivable fungi were found in six samples and with a median concentration below detection level. Using microscopy, fungal spores were identified in 22 samples. The components NAGase and (1 3)-β-D-glucans, which are mainly associated with fungi, were present in all PM1 samples. Thermophilic actinomycetes were present in 23 of the 29 PM1 samples [average = 739 colony-forming units (CFU) m–3]. Cultivable and ‘total bacteria’ were found in average concentrations of, respectively, 249 CFU m–3 and 1.8 x 105 m–3. DNA- and RNA-containing particles of different lengths were counted by microscopy and revealed a high concentration of particles with a length of 0.5–1.5 µm and only few particles >1.5 µm. The number of cultivable fungi and β-glucan in the total dust correlated significantly with the number of DNA/RNA-containing particles with lengths of between 1.0 and 1.5 µm, with DNA/RNA-containing particles >1.5 µm, and with other fungal components in PM1 dust. Airborne β-glucan and NAGase were found in PM1 samples where no cultivable fungi were present, and β-glucan and NAGase were found in higher concentrations per fungal spore in PM1 dust than in total dust. This indicates that fungal particles smaller than fungal spore size are present in the air at the plants. Furthermore, many bacteria, including actinomycetes, were present in PM1 dust. Only 0.2% of the bacteria in PM1 dust were cultivable.
Keywords: actinomycetes • aerodynamic diameter of fungi • bacteria • bioaerosol • biofuel • exposure • inhalable dust • PM1 dust
Received January 29, 2008; in final form June 11, 2009