Fungal Fragments and Fungal Aerosol Composition in Sawmills

Abstract

Assessment of exposure to fungi has commonly been limited to fungal spore measurements that have shown associations between fungi and development or exacerbation of different airway diseases. Because large numbers of submicronic fragments can be aerosolized from fungal cultures under laboratory conditions, it has been suggested that fungal exposure is more complex and higher than that commonly revealed by spore measurements. However, the assessment of fungal fragments in complex environmental matrix remain limited due to methodological challenges. With a recently developed immunolabeling method for field emission scanning electron microscope (FESEM), we could assess the complex composition of fungal aerosols present in personal thoracic samples collected from two Norwegian sawmills. We found that large fungal fragments (length >1 µm) dominated the fungal aerosols indicating that the traditional monitoring approach of spores severely underestimate fungal exposure. The composition of fungal aerosols comprised in average 9% submicronic fragments, 62% large fragments, and 29% spores. The average concentrations of large and submicronic fragments (0.2–1 µm) were 3 × 105 and 0.6 × 105 particles m−3, respectively, and correlated weakly with spores (1.4 × 105 particles m−3). The levels of fragments were 2.6 times higher than the average spore concentration that was close to the proposed hazardous level of 105 spores per m3. The season influenced significantly the fungal aerosol concentrations but not the composition. Furthermore, the ratio of spores in the heterogeneous fungal aerosol composition was significantly higher in saw departments as compared to sorting of green timber departments where the fungal fragments were most prevalent. Being the dominating particles of fungal aerosols in sawmills, fungal fragments should be included in exposure-response studies to elucidate their importance for health impairments. Likewise, the use of fungal aerosol composition in such studies should be considered.

Fungal aerosol composition in moldy basements

“…In our study, SF were found only in two indoor samples at average concentrations (0.02‐0.05 × 10 3 m −3 ) and were significantly below the spore concentrations. These data are consistent with previous findings in sawmills, but departs largely from levels measured in aerosolization studies and (1, 3)‐β‐glucans‐based projections, that is, that the spore concentrations are significantly higher than that of submicron fragments. The low levels of SF in present study may be due to the differences in the aerosolization mechanisms governing the release of these particles from fungal biomass in the indoor settings as compared to laboratory experiments.…”

“…The procedure used here was described elsewhere . Briefly, the composition of fungal aerosols including spores (S), submicron fragments (SF, length: 0.2‐1 µm), and larger fragments (LF, length: >1 µm) in the samples was assessed using a FESEM (SU 6600 HITACHI) operated at low vacuum (25‐30 Pa) and in the back‐scattered electron (BSE) imaging mode.…”

“…Further, we applied linear mixed effect regression analysis with interaction terms to depict changes in the fungal aerosol composition in indoor versus outdoor (I/O) and between summer and autumn (seasons). To achieve this, we used centered log ratio (clr) transformed percentages of the particle types as reported previously . Schematically, the models were as follows:(where “Types” included spores, submicron fragments, and larger fragments, “I/O” for indoor outdoor, and “Season” included autumn and summer).…”

“…A recently developed method combining immunogold labeling and field emission scanning electron microscopy (IGL‐FESEM) enabled us to identify and enumerate submicrometer fungal fragments as well as large fragments and spores in complex environmental air sample matrix. When this method was applied to personal samples collected in sawmills, we found a substantial proportion of fragments including submicrometer (9%) and larger fragments (62%) in addition to spores in the fungal aerosols . We therefore aimed at a detailed characterization of the fungal aerosols, including spores and fragments in the submicrometer and larger size ranges, in moldy basements of townhouses and simultaneously in outdoor air.…”

Mould in building disputes

“…Optical techniques include measuring the cumulative particle number concentration (particulate matter size distribution) based on size 46 rather than mass using an optical particle counter 47 since it has recently been found that large fungal fragments (>1µm) are under-sampled by traditional monitoring approaches, thereby underestimating actual fungal exposure. 48 Regardless of methodology, it is very important to collect suitable controls for the outdoor area as well as from the complaint/region of interest areas as well as those immediately adjacent to such areas. Suitable indoor controls which include non-complaint rooms or regions should be collected.…”