Thanks to new University of Colorado Boulder research, scientists see the impact of flushing the toilet in a whole new light — and now, the world can as well.
Using bright green lasers and camera equipment, a team of CU Boulder engineers ran an experiment to reveal how tiny water droplets, invisible to the naked eye, are rapidly ejected into the air when a lid-less, public restroom toilet is flushed. Published in Scientific Reports, it is the first study to directly visualize the resulting aerosol plume and measure the speed and spread of particles within it.
These aerosolized particles are known to transport pathogens and could pose an exposure risk to public bathroom patrons. However, this vivid visualization of potential exposure to disease also provides a methodology to help reduce it.
“If it’s something you can’t see, it’s easy to pretend it doesn’t exist. But once you see these videos, you’re never going to think about a toilet flush the same way again,” said John Crimaldi, lead author on the study and professor of civil, environmental, and architectural engineering. “By making dramatic visual images of this process, our study can play an important role in public health messaging.”
Researchers have known for over 60 years that when a toilet is flushed, solids and liquids go down as designed, but tiny, invisible particles are also released into the air. Previous studies have used scientific instruments to detect the presence of these airborne particles above flushed toilets and shown that larger ones can land on surrounding surfaces, but until now, no one understood what these plumes looked like or how the particles got there.
Understanding the trajectories and velocities of these particles — which can transport pathogens such as E. coli, C. difficile, noroviruses and adenoviruses — is important for mitigating exposure risk through disinfection and ventilation strategies, or improved toilet and flush design. While the virus that causes COVID-19 (SARS-CoV-2) is present in human waste, there is not currently conclusive evidence that it spreads efficiently through toilet aerosols.
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