Do you wash a public toilet? Do not linger, because aerosolized droplets exist

Washing a toilet can generate large amounts of aerosols that contain microbes, depending on the design, water pressure or washing power of the toilet. A variety of pathogens are usually found in stagnant water, as well as in urine, feces and vomit. When widely dispersed by aerosolization, these pathogens can cause Ebola, a norovirus that results in violent food poisoning, as well as COVID-19 caused by SARS-CoV-2.

Respiratory drops are the most prominent source of COVID-19 transmission, however, there may be alternative routes, given the discovery of a small number of viable viruses in urine and stool samples. Public toilets are of particular concern for the transmission of COVID-19, as they are relatively limited, have heavy traffic on the ground and may not have adequate ventilation.

A team of scientists from the College of Engineering and Computer Science at Florida Atlantic University has once again tested fluid physics to investigate droplets caused by washing a toilet and a urinal in a public toilet under normal ventilation conditions. To measure the drops, they used a particle counter placed at different heights of the toilet and urinal to capture the size and number of drops generated during washing.

The results of the study, published in the journal Fluid physics, to demonstrate how public toilets could serve as foci for the transmission of airborne diseases, especially if they do not have adequate ventilation or if the toilets do not have a lid or lid. Most public restrooms in the United States are often not equipped with toilet seat covers, and urinals are not covered.

For the study, the researchers obtained data from three different scenarios: toilet washing; washing the covered toilet and washing the urine. They examined the data to determine the increase in aerosol concentration, the behavior of droplets of different sizes, how high the droplets increased and the impact of toilet coverage. Ambient aerosol levels were measured before and after the experiments.

“After about three hours of testing involving more than 100 flushes, we found a substantial increase in measured levels of aerosols in the environment, with the total number of drops generated in each wash test varying to tens of thousands.” , said Siddhartha Verma, Ph.D., co-author and assistant professor in the FAU Department of Ocean and Mechanical Engineering. “Both the toilet and the urinal generated large amounts of droplets smaller than 3 micrometers, presenting a significant risk of transmission if they contain infectious microorganisms. Due to their small size, these drops can remain suspended for a long time.”

Drops were detected at heights of up to 5 feet for 20 seconds or more after cleaning began. The researchers detected a smaller number of drops in the air when the toilet was washed with a closed lid, though not by much, suggesting that the aerosolized drops escaped through small gaps between the lid and the chair.

“The significant accumulation of aerosolized droplets generated by color over time suggests that the ventilation system was not effective in removing them from the enclosure, even though there was no noticeable lack of airflow in the toilet,” said Masoud Jahandar Lashaki, Ph.D. .D. , co-author and assistant professor in the Department of Civil, Environmental and Geomatics Engineering of FAU. “In the long run, these aerosols could increase with rising currents created by the ventilation system or by people moving in the toilet.”

There was a 69.5 percent increase in measured levels for 0.3 to 0.5 micrometer particles, a 209 percent increase for 0.5 to 1 micrometer particles, and a 50 percent increase in percent for particles of sizes 1 to 3 micrometers. In addition to the smaller aerosols, relatively larger aerosols also present a risk in poorly ventilated areas, even if they have a stronger gravitational decantation. It often undergoes rapid evaporation into the environment and the resulting decrease in size and mass, or the eventual formation of droplet nuclei, can allow microbes to remain suspended for several hours.

“The study suggests that incorporating adequate ventilation into the design and operation of public spaces would help prevent the accumulation of aerosols in high-occupancy areas, such as public toilets,” said Manhar Dhanak, Ph.D., co-author, president of Department of Ocean and Mechanical Engineering, and professor and director of SeaTech. “The good news is that it may not always be necessary to overhaul the entire system, as most buildings are designed according to certain codes. It may just be a matter of redirecting airflow depending on the appearance of the toilet.”

During the 300-second sampling, the toilet and urinals were manually washed five different times at the 30, 90, 150, 210, and 270-second mark, with the wash handle held down for five consecutive seconds. The toilet was thoroughly cleaned and closed 24 hours before the experiments, the ventilation system working normally. The temperature and relative humidity in the toilet were 21 degrees Celsius (69.8 degrees Fahrenheit) and 52%, respectively.

“Spray drops play a central role in the transmission of various infectious diseases, including COVID-19, and this latest research by our team of scientists provides additional evidence to support the risk of transmitting the infection indoors and in poorly ventilated areas,” said Stella. Batalama, Dr., Dean of the College of Engineering and Computer Science.