Review of 'The environmental dangers of employing single-use face masks as part of a COVID-19 exit strategy'

We have revised our paper to respond to these comments as follows:

"This paper highlights the dangers of trying to rush something into print without prior peer review because the subject is topical. Unfortunately, it is seriously flawed and already out-of-date."

We recognised at the beginning of the Covid19 pandemic that we had only two weeks to do an initial analysis and publish data to help government formulate science-based policy on face masks. Peer review came after our preprint had been fed to government policy makers and although we understand the reviewer’s concerns, in times of emergency we believe it was important to do all we could in the short time-frame available. We used the UCL Press platform to openly publish the data and analysis so everyone could scrutinise it. We believe this was the right thing to do in the spirit of open science and evidence based decision making. The preprint has been viewed more that 4000 times which indicates the high demand for this type of analysis. We apologise for any frustration caused and are very grateful to the reviewer for their time and patience in helping us improve this analysis.

"Its title plainly states it is about “the environmental dangers of single use masks”. As this was not something I had read about before, it provoked my interest. I was disappointed to discover that the title is seriously misleading.  The main text runs to about 11 pages, but only 25% of it relates to a comparison of the environmental impacts of single use and reusable masks. The rest covers: the type and anatomy of masks; their effectiveness; the role of mask-wearing; and behaviour change considerations for reusable mask use. The main findings of the environmental impact study are not even included in the abstract or the conclusions."

We agree about the Conclusions that they did not adequately summarise the paper.  We are confused about the comments about the Abstract. As initially submitted it had four bullet points dedicated to the environmental impact of masks, including the quantitative finding “If every person in the UK used one single-use mask each day for a year, that would create 66,000 tonnes of contaminated plastic waste and create ten times more climate change impact than using reusable masks.” We have updated the Abstract and combined the Discussion and Conclusions into a single section.

"A more appropriate title would therefore be something like:'A comparison of the use by the general public of single-use or re-usable face masks: effectiveness, availability, environmental impact and behaviour considerations.'"

We agree. We have changed the title to “The impact and effectiveness of the general public wearing masks to reduce the spread of pandemics in the UK: a multidisciplinary comparison of single-use masks versus reusable face masks.”

"That the paper has ended up being so different from what the title promises seems to be because it was written by a committee. As the acknowledgements indicate, each section was written by a different pair or trio of people. Perhaps it was felt important that each were given their “fair share” of the manuscript, even if it wasn’t strictly relevant to the aim and title of the paper."

We agree. We have reorganised the paper and taken more focus into highlighting how the different disciplines feed into the analysis. 

"The Conclusions are written by someone else entirely. They refer to “reusable PPE mask(s)” seven times, whereas the phrase doesn’t appear once in the rest of the text!  This author seems to have forgotten that the paper was supposed to be about “the environmental danger of single-use masks”.   (S)he does not even refer to the results of the study of the environmental impact that their colleagues conducted or their conclusions. (S)he also include the sentence: “If washing items that are likely to cause illness (high-risk), the NHS recommends that they should be washed at 60°C with a bleach-based product.”  No-where else in the text is a “bleach-based” product mentioned. The manual wash assumptions used in the study were “detergent in mildly warm water”. The machine wash assumptions were for “detergent” and 40°C. And, as anyone familiar with washing with bleach will know, it can have a disastrous effect on coloured fabrics!"

The Conclusions are now integrated into the Discussions. Terminologies for different masks were made consistent. The NHS recommendation on washing was checked / updated and has been incorporated into main text. The LCA did model washing at 40ºC for machine wash, originally because (Bloomfield et al., 2011) detailed various effectiveness for laundering, one states that “normal” laundering produced 88.9%  reduction (of Shigella infection). Both NHS and CWA 17553 do recommend 60ºC however we assume (as the reviewer notes) that most households are not using bleach but instead using 40ºC machine washes.

"What about the environmental impact assessment itself?  Although the paper was published on May 3 2020, it is already out of date. In the introduction, they state: “The aim of this paper is to examine the environmental impact of the UK adopting masks for the general population in particular the amount of contaminated plastic waste produced.”  Later in the paper it states: “Within the UK, the use of face masks has not yet been identified as a behavioural strategy for reducing the transmission of COVID-19 among the general population.”"

This has now been updated. The new aim of the paper is to provide a multidisciplinary analysis to advise government on what to consider for future pandemics (when mask shortages may not be an issue).

"The UK government has now made it clear they are strongly recommending people wear “face-coverings” when on public transport or in shops, or in other situations such as work where social distancing cannot be maintained. They have made it clear that these should preferably be re-usable and definitely not medical grade.  I have never heard or seen any reference in government guidance to a recommendation that a disposable filter should be used in the reusable mask."

We wrote this paper and posted our analysis on this open access platform before the government published it recommendations.  Disposable filters are not within governmental guidelines but they are available on the market. We believe it is important to highlight the different options available both now and in the future. A table is now included under mask anatomy and standalone effectiveness to showcase the different mask options and their filtration efficiency.

"Consequently, Scenarios 1, 3 and 5 are not going to happen. Scenario 1, with every person wearing a mask every day, did seem rather unrealistic, given that many people don’t go out every day and it is recommended that young children don’t wear masks. The assertion that “this would create over 124,000 tonnes of unrecyclable plastic waste (66,000 tonnes of contaminated waste and 57,000 tonnes of plastic packaging” could thus be exaggerated, even if Scenario 1 was going to happen."

It is clear even now that single-use masks are being sold and worn frequently in the UK. In some other countries such as China, single-use masks are the norm, so we believe Scenario 1 is important to model. Similarly, Scenarios 3 & 5 also represent a proportion of behaviours. In Scenario 1, we agree that not everyone goes out every day but those that do for work or otherwise may balance out overall mask usage. Under correct usage, single-use masks should be discarded after use or after use of 4-6 hours, this means someone going out for work will need at least 2 masks. Although children under 11 do not need to wear masks, some parents are asking their children to wear them.  An explanation of our assumptions has been added into the environmental impact section of the paper.

"The washing assumptions in Scenarios 2 and 3 also seem unrealistic, involving large amounts of hot water per mask. As the Government has been saying for months, washing your hands thoroughly with soap and water is very effective at killing the virus (because it breaks down the virion’s outer lipid layer.) The same should apply to re-usable masks – a quick scrub with soap or detergent in warm water, a thorough rinse with cold water and then leave to dry."

MacIntyre et al. (2020) performed a randomised control trial of hospital health workers in Vietnam and showed that hand washed reusable masks doubled the risk of those worked contracting seasonal respiratory viruses compared to washing the masks in the hospital laundry. If this data is applicable to Covid-19 infections then manual washing will have a different outcome than laundry washing. In terms of manual wash protocols which we can follow, UK taps on average flow 4-6 L/min (Department for Environmental Food & Rural Affairs, 2014), depending on the person, they can leave the tap running whilst applying soap and/or because fabric may retain soap and liquid more readily than our hands a longer rinse maybe necessary. We believe washing masks in tubs as the manual wash technique to be more sustainable than running water.  An explanation on our assumptions has been added to the Appendix.

"The presentation of the results could be improved. For example, in Table 2 the Units are not explained."

Units are now stated in the paper.

"Figure 1 is very difficult to fully understand with so many different categories in stacked columns. It does seem odd that the  CO2  equivalent  of “Mask Use”  is so much greater for manual wash than machine wash. The category might better be “Mask wash” and perhaps the difference is down to the assumptions about the manual washing assumptions I questioned above."

“Mask Use” was chosen as the process name to signify all the required activities while the mask is in use before disposal. More water is required for manual washing, which also means that more energy is required to heat water. Energy generation is the main contributing factor towards Climate Change. A note about this has been added to the appendix to make it clearer.

"Nevertheless, by the authors’ reckoning, machine washed re-usable masks without filters are by far the most environmental-friendly form of mask wearing by the general public. This seems to be the key novel and useful finding in the paper, but it is not mentioned in the abstract or the conclusions.  Amazing!"

We agree. We have added this to the Abstract and Discussion & Conclusions.

"There are many other smaller details in the paper that careful editing would have improved."

For example, on page 8 there are the sentences:

"“The use of masks may give users a false sense of protection, thus encouraging risk-taking."

No mask protects against the transmission of a virus through direct contact, and hand washing is essential prior to using, and after removing it.”

"The same sentences appear in the next section. (Did one team cut and paste from the other?)"

In page 10 it states: “Considering that the half-life of the virus is 5.6 hours”. This is not referenced, but it is clear that virus viability varies greatly according to the medium it is in or on, temperature, exposure to sunlight etc.

"I think these are signs of the haste with which the authors rushed to get the paper into print, without careful consideration of every word."

Thank you, we have corrected these.