Concentrations of bacteria and bacterial and fungal spores calculated from chemical tracers associated with size-segregated aerosol in a composting plant

The lack of information on biological risks in workplaces arises from the difficulty to measure bioaerosol. This study aimed to develop and improve the bioaerosol monitoring technique that uses proper biomarkers as a tool. Muramic and dipicolinic acids, and ergosterol were used as tracers for bacteria cells, bacterial spores, and fungal spores, respectively. Furthermore, 12- and 13- methyltetradecanoic acids (iso- and anteiso- C15:0) were used to study the presence of airborne bacteria and 3-hydroxy fatty acids were used to determine the concentration of peptidoglycan. Airborne particulate matter was sampled in a municipal indoor waste composting facility by multistage impactor samplers, during three main stages of composting process. The microorganism content, in airborne particles with aerodynamic diameter minor then 1 μm and between 1 and 10 μm, was determined starting from the aforementioned biomarker concentrations. For iso- and anteiso- C15:0, a conversion factor to transform its concentra- tion into bacterial content was tentatively proposed. The results show that the chemical method covers some gaps in the information about bioaerosol presence in polluted atmospheres. Differences up to two orders of magnitude are observed, by comparing the results obtained by biomarkers and by cultivation-dependent methods. The microbial content, expressed as a percentage by mass on respect the PM, ranged from 4 to 28% with higher percentages during shredding and mixing stages and lower values during biocell opening operations. Bacterial spores, bacterial cells, and fungal spores detected were high in number, compared with the findings in similar studies elsewhere.