## 4 Discussion
The values of total and respirable fractions of fungal aerosol both in the Krakow and Tarnow stables are similar to the ones reported by [PERSON] et al. [5] or [PERSON] et al. [6], who observed the total fungal aerosol concentrations within the ranges of 10\({}^{3}\)-10\({}^{4}\) CFU/m\({}^{3}\) and lower than the ones reported by [PERSON] et al. [24], who reported the total fungal aerosol concentrations exceeding 1 \(\times\) 10\({}^{6}\) CFU/m\({}^{3}\) in the Swedish stables. However, respirable fractions of fungal aerosol reported by [PERSON] et al. [24] were similar or somewhat higher to the results observed in our study. Due to the absence of regulations in Poland, the observed fungal aerosol concentrations were compared to the proposal of the Team of Experts in Biological Factors (Pol. : ZECB) [18] on the concentrations of airborne microorganisms, treating animal rooms as organic dust-contaminated working premises, which is 50,000 CFU/m\({}^{3}\) for the total fraction and 25,000 CFU/m\({}^{3}\) for the respirable fraction of fungi. In this respect, the concentrations of both total and respirable fraction of fungal aerosol exceeded the suggested values only once, i.e., during feeding of horses and only in the Krakow stable. According to [PERSON] [25], the age and type of ventilation in the animal premises may be among the important factors affecting the concentrations of bioaerosol. In our study, both stables have a gravitational type of ventilation. The Krakow stable has two ventilation channels (0.4 \(\times\) 0.4 m), eight windows per building, with an area of 300 m\({}^{2}\) and 900 m\({}^{3}\) cubature. The Tarnow stable has six ventilation channels of the same size and thirty-five windows per building with an area of 714 m\({}^{2}\) and 2360 m\({}^{3}\) cubature. In this respect, it can be assumed that both buildings are characterized by similar type and efficiency of ventilation. Another important factor in terms of indoor bioaerosol levels is the share of respirable fraction. The greater share of respirable fraction in the total concentration of bioaerosol, the greater share of its particles can reach the lower respiratory tract of animals and people present in the stables [15]. According to [PERSON] [26], occupational exposure to small sized bioaerosols may cause not only infections related to the direct contact with microorganisms, but also may cause the diseases related to the mycotoxin and fungal glucan exposure. Among the consequences of respirable fraction of bioaerosol exposure are diseases such as bronchitis, obstructive pulmonary disease, allergic asthma, alveolitis, or organic dust toxic syndrome [15]. [PERSON] et al. [27] observed the share of respirable fraction of bioaerosol exceeding 80% and suggested that this might contribute to the occurrence of not only allergic symptoms--respiratory tract diseases and such concentrations should be also treated as a disturbing observation. The percentage of respirable fraction observed in our study also suggests that the RF levels indoors might pose a risk to the animals and people staying indoors, as they have the potential to deposit in the tracheal, bronchial, or alveolar regions of the lungs [27]. We also attempted to find out whether there is a correlation between the fungal aerosol levels (and its fractions) and other parameters measured in this study, such as PM\({}_{10}\), PM\({}_{25}\), PM\({}_{1}\), temperature, and relative humidity. Interestingly, we observed different regularities in the case of the two examined horse stables. The relationship between fungal aerosol fractions and particulate matter levels was more evident in the Tarnow stable than in Krakow, where fungal aerosol fractions seem not to be dependent on any of the other measured parameters. On the other hand, the changes in the fungal aerosol concentrations in Tarnow strictly follow the pattern of particulate matter and correlate significantly with all PM fractions, as well as with temperature (positive correlation) and relative humidity (negative correlation).