Microplastic Analysis in Soil Using Ultra-High-Resolution UV–Vis–NIR Spectroscopy and Chemometric Modeling
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe paper entitled: Microplastic analysis using ultra-high resolution UV-VIS-NIR 2 spectroscopy is focused on: the validation of UV-VIS-NIR spectroscopy to identify and quantify concentrations of soil microplastics.
First of all, the authors did not enter addresses and emails, not even that of the corresponding author, furthermore throughout the text the characters are not always the same and there are often ty** errors (e.g. spaces). Furthermore, some items were not filled in Funding, Institutional Review Board Statement, Informed Consent Statement, Data Availability Statement, and Conflicts of Interest. This gives the impression that the paper was written quickly and superficially.
The title is not consistent with the abstract and the text, in fact, from the title it is not possible to deduce that we are talking about analyses carried out on soil samples.
In the introduction we only talk about two methods for the characterization of microplastics, the authors did not mention all the existing methodologies, just as the novelty and general importance of this study compared to other methods were not well highlighted.
I found only one work related to this study, that of Corradini et al. 2019 and I don't see any great scientific news compared to what has already been published.
Materials and methods
Only experimental tests were carried out while it would have been interesting to also make a comparison with environmental samples to see if the proposed method works. I haven't seen any statistical analysis. The conclusions are based only on a prediction and do not seem real to me. The bibliography is limited
Author Response
Reviewer 1:
The paper entitled: Microplastic analysis using ultra-high resolution UV-VIS-NIR 2 spectroscopy is focused on: the validation of UV-VIS-NIR spectroscopy to identify and quantify concentrations of soil microplastics.
Reviewer: First of all, the authors did not enter addresses and emails, not even that of the corresponding author, furthermore throughout the text the characters are not always the same and there are often ty** errors (e.g. spaces). Furthermore, some items were not filled in Funding, Institutional Review Board Statement, Informed Consent Statement, Data Availability Statement, and Conflicts of Interest. This gives the impression that the paper was written quickly and superficially.
Author response: Our apologies. We worked on this collaboratively on Google Drive and different fonts and typographical errors occurred. All these are now corrected. Regarding the various statements, we apologize for the omissions and these are now all completely incorporated using the proper formatting of this journal. .
Reviewer: The title is not consistent with the abstract and the text, in fact, from the title it is not possible to deduce that we are talking about analyses carried out on soil samples.
Author response: We realized this is a valuable comment and agree with the reviewer’s concern. The title has been changed to “Microplastic analysis in soil using ultra-high resolution UV-VIS-NIR spectroscopy and chemometric modeling”
Reviewer: In the introduction we only talk about two methods for the characterization of microplastics, the authors did not mention all the existing methodologies, just as the novelty and general importance of this study compared to other methods were not well highlighted.
Author response: Thank you, we agree and have added in Chromatography-mass spectrometry and Thermal Desorption. The initial reasoning behind only stating 2 (Raman and FTIR) is because they are the most commonly used instruments in the spectral group of instrumentation used - then chromatography and thermal desorption, although not as common compared to Raman and FTIR. We addressed the comment by adding in background on the additional 2 methods and referenced a paper as well. This can be found in lines 49-57 of the revised version.
Reviewer: I found only one work related to this study, that of Corradini et al. 2019 and I don't see any great scientific news compared to what has already been published.
Author Response: We are confused by this comment. The scarcity of previous studies is the motivation of our paper. There is very little soil microplastic study using full range, portable UV-Vis-NIR. Until Corradini et al. 2019’s research, no previous studies were performed using full range portable UV-Vis-NIR. Previous work, which has been referenced- used Raman, FTIR, Chromatography-mass spectrometry and Thermal Desorption. All of these methods have issues that the community wanted resolved. Corradini et al. 2019’s study proved that portable full range UV-Vis-NIR is an enhanced approach compared to what has been used. Our study builds on Corradini’s findings but offers a different approach with a higher spectral resolution (1.5nm, 3.0nm, 3.8nm) than what they used (3.0nm, 8.0nm, 6.0nm) (see lines 68-75 in revision). Our findings suggest that using a higher spectral resolution field portable spectrometer can more accurately identify microplastics and thus enhance the accuracy of chemometric modeling due to the ultra high resolution of the data. More specifically, our study shows that spectral data can be used for quantitative MP identification (prediction) using a chemometric model built from known calibration samples and then tested with multivariate statistical approaches (lines 244-253 in revision). This latter includes comparison with similar quantitative and chemometric findings of Huda et al (2023) and Marchesi et al (2023) in our Conclusion (lines 434-440 in revision).
Materials and methods
Reviewer: Only experimental tests were carried out while it would have been interesting to also make a comparison with environmental samples to see if the proposed method works. I haven't seen any statistical analysis. The conclusions are based only on a prediction and do not seem real to me. The bibliography is limited
Author Response: Thank you. To address each of your comments: 1) Because this is a “proof of concept” study of a new methodology (using portable ultra-high resolution full-spectral analysis) of MP’s we needed to start with a relatively simple unit of study to minimize the unknown variables. We therefore avoided field (environmental samples) which will be composed of several types of variable soil components. Now that this study has produced encouraging results we (and hopefully others in this field) will initiate field studies 2) Our quantitative methods are focused on chemometric modeling and require the generation of the PSLR model statistical analysis. The first type of analysis that was conducted focused primarily on descriptive based statistics. In which the wavelengths for each polymer were measured in terms of mean, variance, and standard deviation. The reason for this is to ensure the validation of the data collected. Some of the errors that descriptive statistics tested for or fixed were the following, identifying data entry errors, assessing data distributions, and detecting missing values. Once the data was validated, comparisons between the data gathered for the generation of the model were compared to that of a pure plastic polymer sample or the vermiculite soil sample. The analytical results of a model can express the relationships between several different variables. The PSLR model that was generated in this study shows a clear relationship between microplastic concentrations and the resulting reflectance value gathered from the mass spectrometer 3) Our conclusions are simply meant to support our hypothesis that our instrumentation and predictive modeling provides encouraging results for the portable ultra-high resolution full-spectral analysis combined with chemometric modeling. 4) We agree that the bibliography is too limited. We have significantly increased it from 24 to 36 references.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
I’ve examined your manuscript, which deals with an internationally urgent issue. You offer a nice approach, which can become really demanded in the international research of microplastics. The manuscript is informative and based on the solid methodological ground. The experiments were carried out properly. The manuscript itself is well-written, although it would be better structured, better illustrated, and better referenced. I also feel that the interpretations should be extended and some important issues should be addressed. I hope my comments given below will help bringing this work in order.
1) General concern: is it ok that the device considered in this study was created by the organization, with which two authors are affiliated? Some readers would judge such a contribution subjective and promoting commercial interests. Please, give some explanations and check for possible ethical issues. And do the authors have permission from this organization? This should also be stated.
2) Title: if this study focuses on soil, this should be reflected in the title (as well as in the objective stated in Introduction).
3) Please, indicate full affiliation with full street address for each author.
4) Key words: please, do not use the words already available in the title.
5) Line 58: which previous lab work? Please, give citations and explain better.
6) Section 2: it would be good to see some photographs of the analyzed substances.
7) Sections 4-6 should be merged into one section to be named “Discussion”.
8) In “Discussion”, you have to compare your approach to what has already been described in the literature. If your approach has no analogs, you have to check how its testing corresponds to the expectations (research needs) of specialists expressed in various publications.
9) In “Discussion”, you have to consider the possible applications of your approach. Is it good for only soil and, if so, of which type(s)? Which kind of plastic pollution (in regard to origin and sources of microplastics) can be addressed with this approach? In which situations and under which conditions (e.g., environmental) can this approach be used? Are there some limitations?
10) “Discussion”: you mention several types of microplastics. Well, this is good, but how common are these types in the real-world pollution. Please, give some examples.
11) References: in my opinion, good papers should bear more representative lists of references. However, if the Authors address my recommendations given above, the number of the cited sources should increase. Please, select only relevant sources!
Author Response
Reviewer 2:
Dear Authors,
I’ve examined your manuscript, which deals with an internationally urgent issue. You offer a nice approach, which can become really demanded in the international research of microplastics. The manuscript is informative and based on solid methodological ground. The experiments were carried out properly. The manuscript itself is well-written, although it would be better structured, better illustrated, and better referenced. I also feel that the interpretations should be extended and some important issues should be addressed. I hope my comments given below will help bring this work in order.
1) Reviewer: General concern: is it ok that the device considered in this study was created by the organization, with which two authors are affiliated? Some readers would judge such a contribution subjective and promoting commercial interests. Please, give some explanations and check for possible ethical issues. And do the authors have permission from this organization? This should also be stated.
Author Response: Thank you. While two authors are affiliated with a company that manufactures this instrument and software, they are fully focused on the objective collection of data and analysis of the data in a rigorous way. Their affiliation has the benefit of providing exceptional technical expertise. Also, they worked in close collaboration with two fully academic researchers at a nationally recognized state University. We do have permission from the company, now stated in the Acknowledgements.
2) Reviewer: Title: if this study focuses on soil, this should be reflected in the title (as well as in the objective stated in Introduction).
Author Response: We understand the reviewers’ concern and it has been corrected in the title and lines line 103 of the revised manuscript.
3) Reviewer: Please, indicate full affiliation with full street address for each author. Author Response: Done
4) Reviewer: Key words: please, do not use the words already available in the title. Author Response: Now corrected. All key words not in title.
5) Reviewer: Line 58: which previous lab work? Please, give citations and explain better.
Author Response: Previous lab work was conducted by Corradini et al. 2019. This study furthers that research by showing the technology can enhance identification and quantification efforts by using a higher spectra; resolution spectrometer than what was previously used by Corradini. See lines 67-76 in revision.
6) Reviewer: Section 2: it would be good to see some photographs of the analyzed substances.
Author Response: We agree. We have added a photograph which is now Figure 1.
7) Reviewer: Sections 4-6 should be merged into one section to be named “Discussion”.
Author Response: We agree with the reviewers’ suggestion by moving these sections to Discussion and also expanding on it more. See esp lines 245-261 in new revision.
8) Reviewer: In “Discussion”, you have to compare your approach to what has already been described in the literature. If your approach has no analogs, you have to check how its testing corresponds to the expectations (research needs) of specialists expressed in various publications.
Author Response: We agree with the reviewers’ suggestion. The expansion of previous sections 4-6, now in Discussion, expands on this. Section 4 is significantly expanded, incl lines 245-261 noted above and esp Section 4.4 lines 388-407 are all newly added to address this.
9) Reviewer: In “Discussion”, you have to consider the possible applications of your approach. Is it good for only soil and, if so, of which type(s)? Which kind of plastic pollution (in regard to origin and sources of microplastics) can be addressed with this approach? In which situations and under which conditions (e.g., environmental) can this approach be used? Are there some limitations?
Author Response: This has been addressed in section 4.4 - Applicability that talks about what was done in the study, how this can be applied to future studies and other soil types/environments and also the limitations in terms of how accurate the model is being based on the idea of good spectral data and model maintenance. This can be found in lines 388-407 of the new revision
10) Reviewer: “Discussion”: you mention several types of microplastics. Well, this is good, but how common are these types in the real-world pollution. Please, give some examples.
Author Response:Thank you, we have now added examples, please see lines 99-102 and lines 419-421 in revised version.
11) Reviewer: References: in my opinion, good papers should bear more representative lists of references. However, if the Authors address my recommendations given above, the number of the cited sources should increase. Please, select only relevant sources!
Author Response: We agree that the bibliography is too limited. We have significantly increased it from 24 to 36 references. Below we describe some specific expanded discussions.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript is focused on the microplastic analysis using ultra-high resolution UV-VIS-NIR spectroscopy. In general, the presented work is very interesting. The research design is appropriated and methods are adequately described. English is fine.
However, the manuscript should be improved before the publication. For this purpose, please, see the comments below:
1. The introduction does not provide sufficient background:
- the aim of the work should be highlighted,
- the Authors wrote 'Finally, very few studies have used ultra-high spectral resolution of 1.5nm, 3.0nm, and 3.8nm to measure the reflectance spectra, with the vast majority of published studies using standard spectral resolution or lower (>3nmUV-VIS, 8nm, 6nm NIR).'
These studies should be cited and described.
2. What is the novelty of the work? What is the difference between this work and papers published before?
3. The Authors cited only 24 publications. Hence, the literature review should be performed once again. In my opinion, 24 papers do not sufficiently present the research topic.
4. The manuscript has been prepared very carelessly. For instance, the quality of Figures 7-11 should be improved. Moreover, information is missing in several places, for example 'Author Contributions'.
5. The obtained results should be compared in more detail with those available in the literature.
3.
Author Response
Reviewer 3:
The manuscript is focused on the microplastic analysis using ultra-high resolution UV-VIS-NIR spectroscopy. In general, the presented work is very interesting. The research design is appropriated and methods are adequately described. English is fine.
However, the manuscript should be improved before the publication. For this purpose, please, see the comments below:
Reviewer: The introduction does not provide sufficient background: aim of the work should be highlighted.
Author Response: Thank you, we have added considerable text to the Intro that more precisely describe the aim of the work: lines 50-58, 66-76, and esp lines 100-116 in the revised version..
Reviewer: the Authors wrote 'Finally, very few studies have used ultra-high spectral resolution of 1.5nm, 3.0nm, and 3.8nm to measure the reflectance spectra, with the vast majority of published studies using standard spectral resolution or lower (>3nmUV-VIS, 8nm, 6nm NIR).” These studies should be cited and described.
Author Response: These studies are now cited in lines 66-67 in the revised version. Several of these are new citations. These are also discussed and cited in the Conclusion lines 433-441 in the new version.
Reviewer: What is the novelty of the work? What is the difference between this work and papers published before?
Author Response: A main novelty of this work is the application of ultra-high resolution spectroscopy to MP analysis instead of the current traditional standard resolution instrument. In order to emphasize this novelty we have added an entire section (Section 3.1) of several paragraphs and 3 new figures (Figs 2-4) that demonstrate the advantage of using ultra-high resolution in MP results. The novelty is that we are raising awareness of a new level of analytical resolution that has not been used by the vast majority of MP researchers. In addition, we have added two paragraphs discussing (with new citations) the applicability of UV-Vis-NIR spectroscopy for microplastic identification (lines 388-406). We also added a paragraph explaining the relatively new approach of quantitative MP identification (prediction) by a chemometric model built from known calibration samples and then tested with multivariate statistical approaches (lines 245-254). This includes new citations involving a comparison with similar quantitative and chemometric findings of Huda et al (2023) and Marchesi et al (2023) in our Conclusion (lines 435-441).
Reviewer:. The Authors cited only 24 publications. Hence, the literature review should be performed once again. In my opinion, 24 papers do not sufficiently present the research topic.
Author Response: We have now added 12 more relevant papers, for a total of 36 papers.
Reviewer: The quality of Figures 7-11 should be improved.
Author Response: This is an excellent point and we have greatly improved and added to our figures as follows: Fig 1-4 are newly added: Fig 1 is a photo of the samples (as requested by another reviewer). Figs 2-4 compares data from an ultra high resolution instrument to a standard resolution instrument. Figs 10-12 were given an updated caption and key. Figs 13-15 were completely redone with an updated caption. Unfortunately, Figs 5-9 cannot be modified because they are produced by the software described in our paper, and it is not amenable to editing.
Reviewer: Moreover, information is missing in several places, for example 'Author Contributions'.
Author Response: Thank you, all this information is now added in the appropriate places at the end of the paper. Lines 463-477
Reviewer: The obtained results should be compared in more detail with those available in the literature.
Author Response: Thank you, we have added considerably more discussion of prior relevant studies, including more citations. These added discussions specifically include more about: 1) other methods of MP analysis such as Pyr-GC-MS and TED-GC-MS (lines 50-58), 2) more studies that have used both standard and high resolution spectroscopy These studies are now cited in lines 66-67 in the revised version. Several of these are new citations. These are also discussed and cited in the Conclusion lines 433-441 in the new version. See also lines 69-76). 3) how our study shows that spectral data can be used for quantitative MP identification (prediction) using a chemometric model built from known calibration samples and then tested with multivariate statistical approaches: (lines 245-254), 4) this latter includes comparison with similar quantitative and chemometric findings of Huda et al (2023) and Marchesi et al (2023) in our Conclusion (lines 435-441).
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsDear authors, I am pleased to note that you have greatly improved the manuscript and therefore in my opinion it can be accepted for publication.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
I'm fully satisfied with your revisions and responses - thank you very much for so responsible work!
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript has been corrected.
