Towards Zoo Sustainability: Assessment of Indoor and Outdoor Bacterial Air Contamination Levels and Their Correlations with Microclimate Parameters

Air quality in zoo premises is insufficiently investigated, yet scientific interest is growing. In these places, air pollutants such as microorganisms may represent health risk for both animals and exposed people. Thus, maintaining good air quality is crucial for ensuring long-term sustainability of zoo operations. The present study aimed to assess bacterial air contamination level and microclimate conditions in Zagreb Zoo. Measurements were performed in the area for visitors and employees inside four premises, i.e., Monkey House, Tropical House, Rainy Africa, and Bird House, as well as outside the premises in the summer–autumn period. Total number of bacteria in the premises ranged from 4.50 × 10 2 to 3.70 × 10 4 CFU/m 3 , and number of Gram-negative bacteria ranged from 0 to 5.50 × 10 2 CFU/m 3 . Total number of bacteria in outdoor air ranged from 50 to 8.50 × 10 2 CFU/m 3 , and number of Gram-negative bacteria ranged from 0 to 50 CFU/m 3 . Total number of bacteria was significantly higher in the Rainy Africa and Bird House as compared to the Monkey House and Tropical House, yielding a significant positive correlation with the number of Gram-negative bacteria in the premises. Total number of bacteria in outdoor air was significantly lower as compared to all investigated premises, except for the Monkey House, yielding a significant positive correlation with the number of Gram-negative bacteria outdoors. Air temperature showed a significant negative correlation with both total number of bacteria and number of Gram-negative bacteria, and airflow rate showed a significant negative correlation with total number of bacteria in the premises. Air temperature showed a significant positive correlation and relative humidity significant negative correlation with total number of bacteria outdoors. Study results can serve in the development of air quality standards in zoos, contributing to finding effective strategies to mitigate health risk from bioaerosols, with implications for occupational and public health, and overall zoo sustainability.