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

The paper is much improved on the previous version.  The flow of the paper is much better and the content more cohesive.  I just have a few minor suggestions:

In the abstract, it is noted that 124,000 tonnes of waste would be created and 66,000 tonnes would be unrecyclable contaminated plastic waste.  Is the remainder recyclable uncontaminated waste?  Please can you explain what this portion is composed of.

The text in the section on European Standards refers to ‘community face masks’ and ‘Community Face Coverings’.  Table 1 refers to ‘Community Masks’.  Are these the same thing?  Could you please clarify?  It would also be useful to explain what is meant by community mask.

The footnote in Table 1 isn’t clear, particularly from ‘but these masks…’ onwards.  Please rephrase.

What are the ‘wash bags’ referred to in the section on Materials and their Filtration Efficiency?

In the Cost Comparison Section under Disposal, the text refers to the weight of a single-use mask.  Strictly speaking, this is mass.

Is there a better way to present the information in Figure 3?  The washing and disposal categories are difficult to make out on the graph.

Could you please check the data in Figure 4?  The Republic of Ireland is highlighted in yellow, but I don’t think this is the case.  It’s also not clear what is meant by ‘yellow indicates countries where mandatory mask use is imposed on part of the country only but their use is recommended by government’.  Do you mean that their use country-wide is recommended but not mandated by government?

There is a sentence in the Discussion and Conclusions section that states that ‘anecdotal evidence in the UK suggests that very few people wear their reusable masks every day’.  It’s not clear what this sentence is meant to tell us and I suggest deleting it.  People mightn’t wear their reusable mask every day for a variety of reasons, like not going anywhere that requires mask use or wearing a disposable mask instead.  It doesn’t necessarily mean that they’re not following the guidelines.

Further on in the discussion, the text states that ‘governments may consider stockpiling masks…’.  Is this referring to single-use masks?  In the last paragraph, the text uses the phrase ‘capacity capable’ – is this the correct phrase?

There are a few minor grammatical errors throughout the paper.  Please give the paper one final proof-read.

General comments. This is a relevant and timely paper on the issue of face coverings used as part of the response to the Covid-19 pandemic. The paper is well-researched, contains interesting perspectives and discussions, and provides important insights on the topic. A key strength of the paper is the collaboration between researchers of different disciplines, but this is also the cause of a related weakness: the article reads like it was written by different authors and does not flow as well as it could. My main recommendation therefore is that article is revised so that the content is more cohesive and the ‘story’ flows better. Further comments are given below, and there are additional mark-ups on the attached file.

Abstract. The abstract contains interesting information, but I’d recommend including more of the numerical results from the analysis, so that the abstract is better related to the findings of the paper. The journal guidelines state that abstracts should be up to 250 words. As it stands, the abstract is just over 300 words, so please reduce the word count in line with the journal guidelines. I’d also recommend writing the abstract as a paragraph rather than as a series of bullet points.

Paper structure and overall content. If section numbers are to be used, then the introduction should be section 1. I’d suggest revising the balance of material in the paper, and/or revisiting the paper title and aims. The paper title and aims are concerned with the environmental impact (is dangers the right word?) of face masks. However less than 3 pages of the main paper directly cover this topic, which isn’t discussed in any detail until page 5. The other content is interesting, but it does not relate directly to the stated aims and title. Also there is some repetition throughout the paper, for example, much of section 5 is already presented earlier in the paper. Please condense the material so as to avoid repetition as far as possible.

Methods. I don't think it's been clearly stated in the main text what the functional unit is for the LCA study (or that FU is an abbreviation of functional unit). Please make sure that the FU is clearly stated in the main text as well as in the appendix so that the reader can properly interpret the results in the main paper. The main text also does not state which impacts are being assessed. Please include this information in the main paper as well as in the appendix (at a minimum please refer to the relevant section of the appendix).

Conclusions. It would be good to include the results of the LCA in the conclusions section, as the paper is concerned with environmental impacts. It would also be useful to relate the conclusions more strongly to the title and the aims of the paper - or to amend the title and aims of the paper? As it stands, there is a disconnect between the paper title and stated aims, and the conclusions.

Appendix. The appendix outlining the LCA work is thorough, well written and clearly presented. However, please make sure that the assumptions used in the analysis match the text in the main paper; there is, for example, some confusion over the washing temperature as different values are given in the conclusions section of the main paper and in the appendix.

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.

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.

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.”

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.

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!

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.” 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.

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.

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.

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

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!

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.