Emission characteristics and quantitative health risk assessment of bioaerosols in an indoor toilet after flushing under various ventilation scenarios

In the indoor environment, toilet is one of the primary sources of bioaerosol because flushing events can disturb stool materials. Bioaerosol exposure has a significant impact on human health. Therefore, this research focused on systematical investigation of Staphylococcus aureus bioaerosol emission characteristics in an indoor toilet after flushing with time. Then, annual probability of infection and disease burden with time under various ventilation scenarios were determined using a Monte Carlo simulation-based quantitative microbial risk assessment. The results showed that at the initial phase, the highest and lowest bioaerosol concentrations were found in poor and combined ventilation scenarios, respectively. The bioaerosol concentration in natural ventilation scenario was 1.1 times higher than that in mechanical ventilation scenario. However, a decreasing trend was observed after flushing. The adult male's health risks were consistently higher than those of all other exposed persons. However, the maximum and minimum health risks were observed in the poor and combined ventilation scenario, respectively. The health risks in the mechanical ventilation scenario were lower than those in the natural ventilation scenario. However, the health infection risk varied with time: it was unbearable to the U.S. Environmental Protection Agency benchmark at 0 min–15 min after flushing, but it was tolerable after flushing 35 min. Moreover, the disease health burdens were below the World Health Organization benchmark after flushing 20 min to 35 min. This research delivered novel data and provide a guideline for controlling the essential health threats from bioaerosol emissions in various toilet usage scenarios.