Spread less particles with urine-diverting toilets

Parents often give their children practical advice: Wash your hands, cover your cough and put the toilet lid down before flushing. Now, researchers from the University of Michigan have published a paper showing that each toilet flush can spit out thousands of virus particles from infected waste.

Parents often give their children practical advice. Wash your hands, cover your cough and put the toilet lid down before flushing. Now, researchers from the University of Michigan have published a paper showing that each toilet flush can spit out thousands of virus particles from infected waste.

The team’s paper, published in ACS ES&T Water, says this amount of virus won’t always lead to an infection. Urine-diverting toilets can reduce a person’s exposure compared to traditional systems.

It’s a well-known fact that flushing a toilet sprays out tiny droplets of water and urine, and feces into the air. These particles land on nearby surfaces or get breathed in by people nearby. But if it’s an infected person’s waste that’s flushed, contagious pathogens, such as noroviruses, adenoviruses and human polyomaviruses, could also be ejected into the air.

Most commodes in the U.S. are of the traditional mix flush type, and they empty one large water-filled compartment. A different kind of toilet is called a urine-diverting system. It has two compartments: one that collects urine in the front and another that removes excrement through the back water-filled compartment. Viruses in urine would be removed through the urine diversion section. However, it’s unclear how much gets sprayed out of those in the water.

Learning more about urine-diverting toilets

So, the team wanted to compare the levels of viruses emitted from flushing to estimate their potential for spreading disease. The researchers added solutions with 10 billion surrogate viruses into the water of the toilets in a university restroom.

They used two bacteriophages: MS2, which is similar to norovirus, and T3, which stood in for adenovirus and polyomavirus. Then the team covered the bowls with plastic film and flushed them. Material from the films was recovered and analysed to see how much MS2 and T3 splashed onto the film.

The results showed that less than one per cent of the virus surrogates added to the toilets sprayed out. When protein was added to the water, the traditional commode expelled tens of times more MS2 and T3 than the urine-diverting version. The researchers also calculated the maximum emissions for different viruses from a single flush.

They estimated up to 390 million and 67 million genome copies of norovirus could be emitted from traditional and urine-diverting toilets. These levels are within the range of an infectious dose.

However, the researchers state that it’s unlikely a person would be exposed to all the particles. Some would probably evaporate, settle onto surfaces or be inactivated by handwashing. The researchers say the next step is determining a person’s risk of contracting these and other diseases from toilet flushing.

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