Flushing toilets eject virus-containing droplets

A flushing toilet releases clouds of virus-containing particles, according to a new study published by the American Institute of Physics. The researchers used a computer model to show that toilet flushing creates large clouds of aerosol droplets that linger in the air long enough to be inhaled.

This presents a new potential pathway for COVID-19 transmission in public restrooms, as recent studies have detected traces of SARS-CoV-2 in the feces and urine of patients.

Toilet flushing creates a great deal of turbulence, and there is evidence to suggest that the force is strong enough to release bacteria and viruses. The public remains largely unaware of this infection pathway because it has not been thoroughly investigated.

In the new study, precise computer models were used to simulate water and air flows in a flushing toilet. 

The researchers used a standard set of fluid dynamic formulas, known as the Navier-Stokes equations, to examine flushing in two types of toilets – one with a single inlet for flushing water, and another with two inlets to create a rotating flow.

The team also used a discrete phase model to replicate the movement of tiny droplets as they are ejected from the toilet bowl into the air. According to the researchers, the results of the simulations were striking.

When a toilet is flushed, water pours into the toilet bowl from one side and strikes the opposite side, creating a vortex. The study revealed that these vortices whirl up above the toilet bowl as high as three feet, suspending virus-containing droplets in the air. The droplets are so tiny that they can float for more than a minute, which is how long they could be inhaled, before settling onto surrounding surfaces. 

“One can foresee that the velocity will be even higher when a toilet is used frequently, such as in the case of a family toilet during a busy time or a public toilet serving a densely populated area,” said study co-author Ji-Xiang Wang of Yangzhou University.

A simple solution to help prevent the spread of viruses in restrooms is to close the lid before flushing. However, in many countries such as the United States, toilets often do not have lids in public restrooms. The researchers recommend a new toilet design that would include a lid that closes automatically before flushing.

The study is published in the journal Physics of Fluids.

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By Chrissy Sexton, Earth.com Staff Writer