Evaluation of Microbial Contamination of the Mist Intended for Inhalation in a Brine Graduation Tower

Abstract The brine mist used for inhalation, produced by the municipal closed-circuit graduation towers, is not subject to microbiological control. There are also no studies on the microbiological safety of brine mist and its potential adverse effects on the health of people inhaling it. Therefore, a two-year study was conducted to evaluate the microbial purity of brine mist intended for inhalation, taking into account the effects of air temperature and brine concentration on microbial cell counts. Bioaerosol was tested for the presence of indicator microorganisms that are epidemiologically significant and may affect the health of inhalers (mould fungi, bacteria, Staphylococcus spp., actinomycetes, Escherichia coli ). The study was conducted over two seasons from April to September in 2021 and 2022. The abundance of actinomycetes and Staphylococcus spp. during the holiday season has increased in this period, due to the high air temperatures. Bacteria and mould counts did not exceed the recommended limits, while E. coli was not found. As the air temperature increased and the brine concentration decreased, the abundance of the microorganisms analysed (especially actinomycetes and Staphylococcus spp.) increased. The study used Bayesian networks which showed that at high temperatures, the probability of Staphylococcus spp. abundance above 73 CFU·m – 3 was 63 % and that of actinomycetes above 8 CFU‧m – 3 was 64 %.