## 4 Discussion  
Personal exposure to airborne animal allergens and endotoxins was studied in a conventional animal facility. Laboratory animal attendants are the worker category at higher risk of exposure to endotoxins Mus m 1 and Rat n 1 than other personnel. This finding is largely expected and confirms the result of our previous study in which different \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **DF** & **SS** & **MS** & **F** & \(p\) \\ \hline Work category & 3 & 207.87 & 69.29 & 9.06 & 0.018 \\ Total exposure time & 26 & 393.71 & 15.14 & 1.98 & 0.23 \\ Work category \({}^{\star}\) Total exposure time & 7 & 139.95 & 19.99 & 2.61 & 0.15 \\ \hline \hline \end{tabular} Notes: DF: degree of freedom; SS: sum of square type III SS; MS: mean square; F: F value, \(p\) value.  
\end{table} 
Table 2: Analysis of variance model of bio-contaminants by work category and total exposure time. Figure 2: Average concentration of bio-contaminants distributed in the four work categories under investigation. activities were compared. Within that study, it was shown that changing cages, performed in animal rooms, and preparation of bedding and distribution of feed, performed in the storage area, are determinant factors in increasing the concentration of the airborne bio-contaminants [24]. In particular, peaks of endotoxin (21.7 ng/m\({}^{3}\)) were found in the storage area, while the highest concentration of the Mus m 1 allergen (61.5 ng/m\({}^{3}\)) was detected in the dirty washing area. The results of personal air monitoring are in agreement with the fact that the animal attendants carried out most of their working tasks in the previously cited environments. Considering the average concentration of the bio-contaminants under investigation by work category (Table 1), the animal attendants showed the highest value of endotoxin (4.59 ng/m\({}^{3}\)) with respect to researchers (0.57 ng/m\({}^{3}\)), researchers who work only in an office (0.56 ng/m\({}^{3}\)) and technicians (0.37 ng/m\({}^{3}\)). This could be due to the fact that, among the various activities carried out by the animal attendants, there are those performed in the storage area, which was found by the authors to be the environment most contaminated by this bio-contaminant. Bedding material, in fact, could be a significant source of accumulation and release of bacterial endotoxins [4; 24; 34]. Even if average doses are below the health-based recommended occupational exposure limit proposed by the Dutch Expert Committee on Occupational Safety (DECOS, 90 EU/m\({}^{3}\) corresponding to about 9 ng/m\({}^{3}\)), two values above the limit were measured for two animal attendants (16.29 ng/m\({}^{3}\) and 9.12 ng/m\({}^{3}\)), confirming that this work category has the highest risk of exposure to these bio-contaminants. Exceeding the recommended limit value is known to be associated with adverse respiratory effects, but also low-dose (<10 ng/m\({}^{3}\)) long term effects cannot be ruled out as scientific evidence for this is provided by several studies [35]. [PERSON] et al. (2017), studying the effect of environmental microbial exposures on the human microbiome in animal care workers, found average endotoxin levels much lower (median: from undetectable to 0.1 ng/m\({}^{3}\)) than the levels found in this study; the discrepancy with the data presented in this study could be explained by the different position of personal samplers (stationary, one meter from the worker) or, more likely, by the use of ventilated cages in the facility analyzed by [PERSON] and co-authors [5]. Regarding rat and mouse allergens, our results showed higher levels for mouse than for rat allergens and confirm the animal attendants as the worker category at higher risk of exposure (15.85 ng/m\({}^{3}\)), followed by technicians (10.67 ng/m\({}^{3}\)), researchers (2.73 ng/m\({}^{3}\)) and researchers in an office (0.08 ng/m\({}^{3}\)).