Not that many people choose to spend any longer than is absolutely necessary in a public toilet, but a new study provides yet another reason to get out of the can as quickly as possible after completing your business. Appearing in the journal Physics of Fluids, the new research reveals how flushing a toilet generates large quantities of aerosolized particles – many of which could contain traces of urine, feces, and even viruses like SARS-CoV-2.
Despite the fact that respiratory droplets are considered to be the main source of transmission for COVID-19, there remains a considerable amount of concern about the role that aerosols may play in spreading the virus. According to the study authors, public toilets are particularly worthy of attention as they tend to be poorly ventilated, and small numbers of viable viruses have been discovered in urine and stool samples.
To investigate the rate at which flushing generates aerosols, the researchers placed particle counters at various heights from both a toilet and a urinal in a public restroom. The facility was deep-cleaned and closed 24 hours prior to the start of the experiment, and is described by the authors as “operating under normal ventilation conditions.”
The researchers flushed both the toilet and the urinal five times over a five-minute period, observing how multiple flushes cause an accumulative build-up of aerosols.
"After about three hours of tests involving more than 100 flushes, we found a substantial increase in the measured aerosol levels in the ambient environment with the total number of droplets generated in each flushing test ranging up to the tens of thousands," explained study author Dr Siddhartha Verma in a statement.
"Both the toilet and urinal generated large quantities of droplets smaller than 3 micrometers in size, posing a significant transmission risk if they contain infectious microorganisms. Due to their small size, these droplets can remain suspended for a long time."
These smaller particles were detected as high as 1.52 meters (five feet) above the toilet, where they were found to linger for at least 20 seconds following a flush. By the end of the five-flush sequence, the researchers noted a 69.5 percent increase in aerosols sized 0.3 to 0.5 micrometers, a 209 percent increase in particles measuring 0.5 to one micrometer, and a 50 percent increase in droplets of one to three micrometers.
Interestingly, covering the toilet with a lid was found to reduce the amount of aerosols by a surprisingly small amount, suggesting that many of these particles are able to escape through the gap between the top of the toilet bowl and the seat.
Commenting on their data, the authors note that “the ventilation system was not effective in removing the aerosols, although there was no perceptible lack of airflow within the restroom.” As a consequence, they conclude that “multiple flushes over time can lead to the accumulation of high levels of potentially infectious aerosols within public restrooms.”
Aside from highlighting the need for improved ventilation in public restrooms – particularly during situations such as a global pandemic – these findings also underline why it isn’t wise to linger around a toilet after flushing.