Where does the carbon go? A new carbon balance method to assess what happens to plastics under solar exposure

Gustave Bertier; Arnaud Martel; Matthieu George; Pascale Fabre; Fabien Boucher; Justine Gérome; Fabienne Lagarde

doi:10.1371/journal.pone.0333021

Peer Review History

Original SubmissionMay 14, 2025
10 Jul 2025 Decision Letter - Wei-Chun Chin, Editor PONE-D-25-25994-->-->Where does the carbon go? A new carbon balance method to assess the fate of plastics under solar exposure-->-->PLOS ONE?> Dear Dr. George, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. Please submit your revised manuscript by Aug 24 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. 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Reviewer #1: No Reviewer #2: Yes Reviewer #3: Yes ******** 2. Has the statistical analysis been performed appropriately and rigorously? -->?> Reviewer #1: N/A Reviewer #2: N/A Reviewer #3: Yes ****** 3. Have the authors made all data underlying the findings in their manuscript fully available??> The PLOS Data policy Reviewer #1: Yes Reviewer #2: Yes Reviewer #3: Yes ****** 4. Is the manuscript presented in an intelligible fashion and written in standard English??> Reviewer #1: No Reviewer #2: No Reviewer #3: Yes ****** Reviewer #1: I find the topic of this paper interesting. Before conducting a detailed review, I first took a general look to understand its contents. However, I believe that this paper is not yet ready for academic peer review. Chapter 2 is titled Methodology and Results, and Chapter 3 is Discussion, while Chapter 4 is Materials and Methods. It is strange to describe the methodology again in Chapter 4 when it has already been presented in Chapter 2. Even if the contents of the two chapters differ, this structure is highly unusual. Moreover, I have never seen a paper that presents both the methods and the results together in a single chapter like Chapter 2 does. I am quite puzzled by the authors’ reasoning behind this structure, and I find it hard to understand. In addition, the methodology is described in a very superficial way. While editing is not the most critical factor in determining the quality of a paper, it should at least be edited sufficiently for reviewers to understand the content properly. However, there are many typographical and formatting errors. In fact, there is even a strange phrase on line 327: “Error! Reference source not found.” This suggests that the authors submitted the paper without even properly proofreading it. Regardless of the content of the paper, I believe it is not ready to undergo peer review in its current state. A substantial and thorough revision is necessary before resubmission. Reviewer #2: The manuscript describes a novel methodology to track the degradation of plastics upon aging, based on measurement of carbon release. The method will be very valuable for the scientific community and further research in the plastic field. However, in general, the manuscript is difficult to read and understand in its current version, requiring a lot of going back and forth, to understand the steps that have been taken. Here I suggest to re-assess the current structure, with a method&result section coming first, followed by a detailed method section later on. For the latter, I also advise to describe the steps of the methods in the order they are conducted. In principle, I suggest to go for a individual results section. Language needs refinement, some examples given below. Some specific recommendations: Line 26: delete "current" Line 31: meaning of "and charges"? Line 76: delete "in the last 4 years" Line 101 (and more later on): link to reference L133: "inherent heterogen. of UV chamber" this needs explaination, it is not fully addressed in the discussion. Why is there hetreogenicity? Line 164: mention already here that open lids were required for oxygen supply. line 250: delete "the quantity" L325: specify whether the magnetic stirrer was covered with plastic, and what would be the consequences L344: Was there a weight loss during cryo milling? If so, is it relevant for subsequent measurements? Figure 3: implies that more carbon mass is lost than polymer mass. So, were there other sources of carbon? Overall, I hence recommend a major revision of the manuscript. Reviewer #3: Although the problem of microplastics is currently addressed in hundreds or thousands of publications, this one can be published because it brings new information. The methodology of analyzing the C balance during degradation seems to be innovative and may be useful to other researchers. I do not have any critical remarks. I suggest the authors to re-edit the manuscript (see line 101) ****** what does this mean? ). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy Reviewer #1: No Reviewer #2: No Reviewer #3: No ******** [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/ . PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org . Please note that Supporting Information files do not need this step. https://doi.org/10.1371/journal.pone.0333021.r001
Revision 1
26 Aug 2025 Author Response We answered to all comments rewritten here in the file "answer to reviewers." Dear Editors and Reviewers, Thank you for your useful comments and remarks. They are addressed in the revised form of the manuscript; the modifications made are detailed thereafter. We acknowledge that we did not explain clearly enough the innovative methodology and the first results that were obtained thanks to it. We have thus made a major revision of the paper, taking into account your recommendations. Moreover, we hope we corrected all the typos that appeared in the previous version. >Reviewer #1: I find the topic of this paper interesting. Before conducting a detailed review, I first took a general look to understand its >contents. However, I believe that this paper is not yet ready for academic peer review. We hope that this revised version qualifies now, since we improved the English and hopefully the clarity of the paper, by modifying its structure in particular. >Chapter 2 is titled Methodology and Results, and Chapter 3 is Discussion, while Chapter 4 is Materials and Methods. It is strange to >describe the methodology again in Chapter 4 when it has already been presented in Chapter 2. Even if the contents of the two chapters >differ, this structure is highly unusual. Moreover, I have never seen a paper that presents both the methods and the results together in >a single chapter like Chapter 2 does. I am quite puzzled by the authors’ reasoning behind this structure, and I find it hard to >understand. In addition, the methodology is described in a very superficial way. Structure was a major drawback of the previous version as were pointed out also by reviewer #2. Our original choice was guided by the necessity to present concomitantly the innovative experimental procedure and the original way to analyse the result by means of a carbon balance, as well as the first results obtained on polypropylene granules. We have changed the structure towards a clearer and more usual one : - A first section entitled “Experimental Section” which includes a sub-section describing the protocole as well as the details of the different techniques - A second section entitled “Results and analysis” that explains how we track step by step where the carbon initially present in the polymer goes and which illustrates this methodology with the results obtained on aged polypropylene granules. - A final section entitled “Discussion” >While editing is not the most critical factor in determining the quality of a paper, it should at least be edited sufficiently for reviewers to >understand the content properly. However, there are many typographical and formatting errors. In fact, there is even a strange phrase >on line 327: “Error! Reference source not found.” This suggests that the authors submitted the paper without even properly >proofreading it. Regardless of the content of the paper, I believe it is not ready to undergo peer review in its current state. A substantial >and thorough revision is necessary before resubmission. We apologize for the topographical and formatting errors that occurred during the submission process. The article has been carefully and thoroughly corrected. We also hired a professional English speaker to proofread and correct the article. >Reviewer #2: The manuscript describes a novel methodology to track the degradation of plastics upon aging, based on measurement of >carbon release. The method will be very valuable for the scientific community and further research in the plastic field. >However, in general, the manuscript is difficult to read and understand in its current version, requiring a lot of going back and forth, to >understand the steps that have been taken. Here I suggest to re-assess the current structure, with a method&result section coming >first, followed by a detailed method section later on. For the latter, I also advise to describe the steps of the methods in the order they >are conducted. In principle, I suggest to go for a individual results section. Structure was a major drawback of the previous version as was pointed out also by reviewer #1. Our original choice was guided by the necessity to present concomitantly the innovative experimental procedure and the original way to analyse the result by mean of a carbon balance, as well as the first results obtained on polypropylene granules. We have changed the structure towards a clearer and more usual one: - A first section entitled “Experimental Section” which includes a sub-section describing the protocole as well as the details of the different techniques - A second section entitled “Results and analysis” that explains how we track step by step where the carbon initially present in the polymer goes and which illustrates this methodology with the results obtained on aged polypropylene granules. - A finale section entitled “Discussion” Language needs refinement, some examples given below. We also hired a professional English speaker to proofread and correct the article. >Some specific recommendations: >Line 26: delete "current" Current has been deleted (Line 26) >Line 31: meaning of "and charges"? Charges refers to the organic or inorganic fillers that can sometimes be added to manufacture a plastic material. This could be misleading as the plastics we studied do not contain charges. We therefore removed “and charges” (Line 31) >Line 76: delete "in the last 4 years" In the last 4 years has been deleted (Line 77) >Line 101 (and more later on): link to reference All links to references have been checked and corrected >L133: "inherent heterogeneity of UV chamber" this needs explanation, it is not fully addressed in the discussion. Why is there heterogeneity? There is inherent heterogeneity in the ageing chamber as the artificial lights do not illuminate the samples with the same UV intensity depending of their position. In the range of possible positions, the samples more towards the middle tend to be more illuminated, resulting in potentially greater photo-oxidation or spontaneous inflammation and therefore greater abiotic degradation for a similar exposure time. This point is stated in both “accelerated ageing chamber” sub-section (lines 152-158) and in “discussion” section (lines 358-362). Expressing the level of photo-oxidation in terms of the carbonyl index (CI) reached makes it possible to overcome this experimental limitation. >Line 164: mention already here that open lids were required for oxygen supply. This point is now stated clearly in the “overall description of the protocol” section (lines 119-121) which comes first in the revised structure. >line 250: delete "the quantity" “the quantity” has been replaced by “the amount” (line 345) >L325: specify whether the magnetic stirrer was covered with plastic, and what would be the consequences The magnetic stirrers used are indeed covered in PTFE. Each magnetic stirrer was thoroughly washed before use and no sign of degradation, or any wear was observed after use. Nevertheless, to avoid counting potential contamination during the NP assessment, the TOC results obtained on blanks that underwent the same protocol (values quickly becoming negligible compared to the quantities of NPs detected as soon as CI 4 is reached) were subtracted. This has been added in the article (line 160-166) >L344: Was there a weight loss during cryo milling? If so, is it relevant for subsequent measurements? It must be noted, that cryo-milling is used exclusively to grind collected aged granules into powder, in order to perform elemental analysis and get averaged carbon content of these degraded products. To make that clearer, cryo-milling technical description has been incorporated into the “elemental analysis” section (lines 183-186). Cryo-milling is thus done independently from the weight measurements. The only possible impact on the analysis would be a potential bias on the average carbon content, if the fraction lost on the walls of the cryo-miller was different from the rest. This fraction being very small (as we recovered almost all the sample), there is no reason to think that this is an actual issue. On the contrary, the cryo-milling step contributes to the agitation and homogenization of the sample in order to reduce as much as possible the bias on the average carbon content. >Figure 3: implies that more carbon mass is lost than polymer mass. So, were there other sources of carbon? This question concerns one of the main arguments underlying the protocol we have established. We therefore hope that things are clearer after these explanations and the rewriting of the article. Figure 3 shows the mass proportion of carbon lost during photo-oxidation in the form of volatiles. For comparison, we have also shown in this figure the proportion of total mass lost by the plastic. During photo-oxidation, two phenomena have opposite effects on the mass of aged plastic. On the one hand, some of the carbon initially contained in the plastic is lost in the form of volatile compounds, which reduces the mass. On the other hand, oxygen is incorporated into the polymer, which increases its mass. The difference observed in Figure 3 between the two curves illustrates this and shows that looking only at the variation in polymer mass masks part of the phenomenon. In other words, the difference between the two curves is solely due to the fact that the total mass loss of the polymer linked to carbon leakage is offset by a mass gain due to its oxidation. All the carbon in the degradation products comes from the polymer. >Reviewer #3: Although the problem of microplastics is currently addressed in hundreds or thousands of publications, this one can be published because it brings new information. The methodology of analyzing the C balance during degradation seems to be innovative and may be useful to other researchers. I do not have any critical remarks. I suggest the authors to re-edit the manuscript (see line 101) We apologize for the topographical and formatting errors that occurred during the submission process. The article has been carefully and thoroughly corrected. We also hired a professional English speaker to proofread and correct the article. Attachments Attachment Submitted filename: Response to reviewers.docx https://doi.org/10.1371/journal.pone.0333021.r002
9 Sep 2025 Decision Letter - Wei-Chun Chin, Editor Where does the carbon go? A new carbon balance method to assess what happens to plastics under solar exposure PONE-D-25-25994R1 Dear Dr. George, We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements. Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication. An invoice will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager® and clicking the ‘Update My Information' link at the top of the page. For questions related to billing, please contact billing support . If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. Kind regards, Wei-Chun Chin Academic Editor PLOS ONE Additional Editor Comments (optional): Reviewer #1: Reviewer #3: Reviewers' comments: Reviewer's Responses to Questions Comments to the Author Reviewer #1: All comments have been addressed Reviewer #3: All comments have been addressed ******** 2. Is the manuscript technically sound, and do the data support the conclusions??> Reviewer #1: Yes Reviewer #3: Yes ****** 3. Has the statistical analysis been performed appropriately and rigorously? -->?> Reviewer #1: Yes Reviewer #3: Yes ****** 4. Have the authors made all data underlying the findings in their manuscript fully available??> The PLOS Data policy Reviewer #1: Yes Reviewer #3: Yes ****** 5. Is the manuscript presented in an intelligible fashion and written in standard English??> Reviewer #1: Yes Reviewer #3: Yes ****** Reviewer #1: I think the revision is good. Now I recommend to accept this manuscript. Thanks for the authors' efforts. Reviewer #3: The work adds interesting information to the current state of knowledge. The authors have responded to my comments. The work may be published. ****** what does this mean? ). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy Reviewer #1: No Reviewer #3: No ******** https://doi.org/10.1371/journal.pone.0333021.r003
Formally Accepted
Acceptance Letter - Wei-Chun Chin, Editor PONE-D-25-25994R1 PLOS ONE Dear Dr. George, I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team. At this stage, our production department will prepare your paper for publication. This includes ensuring the following: * All references, tables, and figures are properly cited * All relevant supporting information is included in the manuscript submission, * There are no issues that prevent the paper from being properly typeset You will receive further instructions from the production team, including instructions on how to review your proof when it is ready. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few days to review your paper and let you know the next and final steps. Lastly, if your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. You will receive an invoice from PLOS for your publication fee after your manuscript has reached the completed accept phase. If you receive an email requesting payment before acceptance or for any other service, this may be a phishing scheme. Learn how to identify phishing emails and protect your accounts at https://explore.plos.org/phishing. If we can help with anything else, please email us at customercare@plos.org. Thank you for submitting your work to PLOS ONE and supporting open access. Kind regards, PLOS ONE Editorial Office Staff on behalf of Dr. Wei-Chun Chin Academic Editor PLOS ONE https://doi.org/10.1371/journal.pone.0333021.r004

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