Flushing a toilet can release microscopic particles into the air, reaching heights within an adult's typical breathing zone, according to a study by scientists at Flinders University. The research, which reviewed over 20 previous studies on aerosols and bioaerosols generated during toilet flushing, highlights the importance of closing the toilet lid before flushing.

Lira Adiyani, lead author of the study, explained that toilet flushing creates turbulence, which can eject aerosols into the surrounding environment. Some studies included in the review detected these aerosols at adult breathing height, suggesting a potential pathway for inhalation exposure.

The researchers found that after flushing, airborne particles can travel up to 4.9 feet (150 centimeters) horizontally and 5.3 feet (163 centimeters) vertically from the toilet. Particles have been observed rising above 100 centimeters from the floor, with the highest recorded height reaching 163 centimeters, placing them within the typical adult breathing zone. These aerosols can remain suspended in the air for at least 20 seconds after flushing.

These airborne droplets can carry microorganisms originating from both the toilet water and the user. The studies analyzed identified various microbes, including E. coli, Salmonella, and Clostridium difficile. Adiyani noted that the quantity of microbes released can depend on the contamination level within the toilet bowl and the flushing water, with larger flush volumes generally producing more aerosols.

To mitigate potential risks, the researchers advise closing the toilet lid before flushing whenever a lid is available. Adiyani recommends this as a precautionary measure to minimize inhalation exposure, while acknowledging that it does not entirely prevent aerosols from escaping.

Previous research, including a 2021 study, also warned that flush-propelled particles, which can contain traces of urine, feces, and viruses, can rise several feet into the air. These tiny droplets and aerosols are light enough to float on air currents before settling on surfaces. Scientists suggest these particles can act as vectors for diseases, and in the context of viruses like SARS-CoV-2, which has been found in human feces, airborne particles from an infected individual could potentially lead to transmission.

The study was published in the journal Science of The Total Environment.