The inhalable mycobiome of sawmill workers: Exposure characterization and diversity

Exposure to fungal spores has been associated with respiratory symptoms and allergic alveolitis among sawmill workers, but the complexity of sawmill workers' fungal exposure has been poorly studied. We characterized the fungal diversity in air samples from sawmill workers' breathing zones and identified differences in the richness, diversity, and taxonomic composition between companies, departments, wood types, and seasons. Full-shift personal inhalable dust samples (n=86) collected from 11 industrial sawmill, sorting mill, and planer mill companies processing spruce and/or pine were subjected to DNA metabarcoding using the fungal internal transcribed spacer (ITS) region 2. The workers were exposed to a higher total number of operational taxonomic units (OTUs) in summer than in winter and when processing spruce than when processing pine. Workers in the saw department had the richest fungal exposure, followed by workers in the planing department and sorting of dry timber department. Sawmills explained 11% of the variation in the fungal community composition of the exposure, followed by season (5%) and department (3%). The fungal compositions of the exposures also differed between seasons, sawmills, wood types, and departments at the taxonomic level, ranging from the phylum to the species level. The differences in exposure diversity suggest that the potential health effects of fungal inhalation may also be different; hence, a risk assessment based on the fungal diversity differences should be performed. This study may serve as a basis for establishing a fungal profile of signature species that are specific for sawmills and that can be measured quantitatively in future risk assessments of sawmill workers.