AFP
Health authorities say the most widespread anti-Covid weapon -- surgical
masks -- must be thrown away after a single use, but environmental concerns
are pushing some scientists to question this recommendation.
As the coronavirus continues to spread, masks have in many places become
mandatory on public transport, in shops and at work.
But cost has become an issue, as has the fact so many disposable plastic
masks wind up in waterways and the oceans.
One alternative is reusable cloth masks, but many people prefer single-use
surgical masks because they are lighter and individually cheaper.
"Medical masks are for single use only," the World Health Organization has
said. "Discard the mask immediately, preferably into a closed bin."
But faced with shortages during the first wave of the Covid-19 pandemic in
March and April, the WHO allowed in a June report for "exceptional
procedures" to disinfect throw-away masks for reuse.
The US Food and Drug Administration (FDA) recommends -- in emergency
circumstances -- hydrogen peroxide vapour to decontaminate the N95 masks
worn by healthcare workers.
Other methods to purify single-use masks include exposing them to high
temperatures or ultraviolet radiation.
But these methods are inconvenient for people at home, said French
microbiologist and member of Adios Corona, Denis Corpet.
Seven-day method
Adios Corona -- a group of scientists who provide information on Covid-19 to
the public -- recommends "placing the mask in a paper envelope with the date
clearly marked, and leaving it for seven days".
"Several scientific studies show that viruses are almost all dead on a mask
after seven days," said Corpet.
A study published in The Lancet found that only 0.1 percent of the virus on
the outside surface of the mask was still detectable after one week.
This method, however, is not appropriate for healthcare workers exposed to
high viral loads.
Peter Tsai, the inventor of N95 electrostatically charged filter material,
agrees with the seven-day method.
But he suggests leaving used masks out in the open for a week before reuse,
a cycle he says can be repeated five to 10 times.
Disposable masks can also be placed in the oven, Tsai told AFP, ideally at a
temperature between 70 and 75 degrees Celsius (158 and 167 degrees
Fahrenheit) -- not too high to avoid burning the plastic, but sufficiently
hot to kill the virus.
Washing masks in a washing machine, however, is not a good idea.
"Washing without detergent may not wash away the virus," Tsai said. "And
washing with detergent will erase the (electrostatic) charges," diminishing
its efficiency.
French consumers' rights group UFC-Que Choisir washed surgical masks at 60C,
put them in the dryer, and ironed them. After 10 such cycles, the masks
still filtered at least 90 percent of 3-micron particles.
"Apart from a slight felting, the washed surgical masks were at least as
efficient as the best cloth masks," UFC-Que Choisir reported last week.
Like underwear
Researcher Philippe Vroman from French engineering university Ensait came to
the same conclusion.
After five washes, "there are practically no differences (of filtration) for
particles of 3 microns," Vroman said, on the basis of preliminary results
not yet published in a peer-reviewed scientific journal.
"And I would rather we swap masks every four hours and wash them, rather
than wearing them several days in a row as some people do. It's a bit like
underwear," he said.
But not all scientists agree.
"Washing the mask at home could potentially cause a secondary contamination
and spread the virus if washing is not set appropriately," said Kaiming Ye,
head of the biomedical engineering department at New York's Binghamton
University.
Until more research is published on the matter, official advice from health
authorities is not set to change.
"Single-use surgical masks must be thrown into the bin after use," said
France's health authority DGS, but noted that more studies were underway.
