Decremental Volumes of Toilet Flushing Water Effects on Bioaerosol Emission Characteristics: Health Risks for Exposure Populations With Nasal/Oral Breathing Patterns

Volume variation of toilet water flushing exhibits an intense association with bioaerosol emissions. However, studies on the effects of toilet flushing water on bioaerosol emissions and their quantitative health risks for exposed populations with various breathing patterns are lacking. This research systematically evaluated Escherichia coli and Staphylococcus aureus bioaerosol concentrations, size distribution, and their decreasing ratio in a dormitory restroom under decremental volumes of toilet flushing water. The experimental measurements were then used as input data for Monte Carlo simulation-based quantitative microbiological risk assessment and sensitivity analysis. The disease burden (DB) was estimated for two exposed populations with nasal/oral breathing patterns, and key contributing input parameters were identified. The result indicates that maximum bioaerosol concentrations were detected in the highest volume of flushing water condition and minimum concentration in the lowest condition. The DB of S. aureus and E. coli bioaerosols in the highest volume of flushing water condition were 2.16-2.36 and 2.20-2.25 times higher than those in the lowest condition, respectively. E. coli and S. aureus bioaerosol DB of nasal breathing pattern were, respectively, 1.44-1.54 and 1.46-1.61 times higher than those of oral breathing pattern. Furthermore, DB of E. coli bioaerosol under various exposure scenarios was intolerable based on the World Health Organization benchmark. However, after flushing at 3.0 L per flush, S. aureus bioaerosol DB satisfied the benchmark. In all exposure scenarios, nasal and oral breathing patterns were nearly identical in terms of their coefficient ranking and percentage ratio. The first substantial contributing input parameter was the deposited concentration of bioaerosol. This study shows that reduced toilet flushing water volume lowers bioaerosol emissions and urban health risks, providing valuable insights for sustainable sanitation approaches that align water conservation with public health.