Micro(nano)plastics and Their Potential Impact on Human Gut Health: A Narrative Review

Round 1

Reviewer 1 Report

Although there are many reviews on the topic, the focus of the paper is interesting; the manuscript is enjoyable to read and requires minor revisions

Line 58: plastic waste based on its polymer size- I suggest: particle size

Line 60: Furthermore, due to potential further degradation and fragmentation, even smaller waste products are derived from microplastics, called nanoplastics - there are also primary nanoplastics

Line 194: C elegans nematode - Caenorhabditis elegans

Caenorhabditis elegans , Artemia  parthenogenetica, Girella laevifrons, Larimichthys crocea,  Oryzias melastigma, Dicentrarchus labrax, Daphnia magna, Pimephales promelas, Staphylococcus, Clostridium, Bifidobacterium,  Prevotella, Veillonella, Ruminococcus; Line 377: Lactobacillus, Adlercreutzia, Butyricimonas and Parabacteroides;  - I suggest italics

Line 220: when exposed to microplastic fibers, the …- The authors should mention microfibers in the Introduction section

Line 364- 365- 367, 369: Lu et al. (year?) Jin et al. (year?) Luo et al.(year’); Jiang  et al. (year’) [110] and Qiao et al. (year?)[111]  Liu, Lv, et al. (year?)  [112]  delete: Lv,

Line 390: Arthrobacter, Bacillus, Micrococcus, Pseudomonas, Corynebacterium, Streptomyces, and Nocardia - I suggest italics

Author Response

Dear editorial assistant and reviewers,

sincerely grateful for the invitation received for the writing of this manuscript, we have made the content changes requested by the reviewers. Below are the clarifications and responses to the comments made by the reviewers.

Reviewer #1

Although there are many reviews on the topic, the focus of the paper is interesting; the manuscript is enjoyable to read and requires minor revisions.

--Line 58: plastic waste based on its polymer size- I suggest: particle size

Response: We thank the reviewer for the comment. We modified it as suggested.

--Line 60: Furthermore, due to potential further degradation and fragmentation, even smaller waste products are derived from microplastics, called nanoplastics - there are also primary nanoplastics

Response: We thank the reviewer for the clarification. We modified it as suggested.

--Line 194: C elegans nematode - Caenorhabditis elegans

Caenorhabditis elegans , Artemia  parthenogenetica, Girella laevifrons, Larimichthys crocea,  Oryzias melastigma, Dicentrarchus labrax, Daphnia magna, Pimephales promelas, Staphylococcus, Clostridium, Bifidobacterium,  Prevotella, Veillonella, Ruminococcus; Line 377: Lactobacillus, Adlercreutzia, Butyricimonas and Parabacteroides;  - I suggest italics

Response: We thank the reviewer for the comment. We modified it as suggested.

--Line 220: when exposed to microplastic fibers, the …- The authors should mention microfibers in the Introduction section

Response: We thank the reviewer for the clarification and would therefore like to provide a comment in the introduction.

--Line 364- 365- 367, 369: Lu et al. (year?) Jin et al. (year?) Luo et al.(year’); Jiang  et al. (year’) [110] and Qiao et al. (year?)[111]  Liu, Lv, et al. (year?)  [112]  delete: Lv,

Response: We thank the reviewer for the comment. We modified it as suggested.

--Line 390: Arthrobacter, Bacillus, Micrococcus, Pseudomonas, Corynebacterium, Streptomyces, and Nocardia - I suggest italics

Response: We thank the reviewer for the comment. We modified it as suggested.

Reviewer 2 Report

The content of the review with the title “Intestinal toxicity of nano- and microplastics in humans and the role of gut microbiota: new insights from in vitro and in vivo research”, does not fulfill the expectations associated with the title for the following reasons:  

1. Most cited papers were published before 2021 and are included in other reviews on the same topic.
2. There is no separation of nano- and microplastic. The indication of the sizes, for which the statements apply, is usually missing.
3. What are the specific insights that were gained by specific in vitro and in vivo studies, e.g. how did the invertebrate studies contribute to the gain of knowledge. Are they suitable for the assessment of these particles?
4. The difficulty to measure the levels of nano- and microplastic was not addressed but has a great impact on the interpretation of the data.
5. Conflicting data were not discussed, e,g, the microparticle content in fruits and vegetables was reported quite differently and only one publication is cited.
6. The issue of plasticizer is not addressed.
7. The relevance of the exposure doses/concentrations is not indicated.
8. The effects on microbiota are listed – what is the relevance?

Typing error:

l.250: piristine

Author Response

Dear editorial assistant and reviewers,

sincerely grateful for the invitation received for the writing of this manuscript, we have made the content changes requested by the reviewers. Below are the clarifications and responses to the comments made by the reviewers.

Reviewer #2

The content of the review with the title “Intestinal toxicity of nano- and microplastics in humans and the role of gut microbiota: new insights from in vitro and in vivo research”, does not fulfill the expectations associated with the title for the following reasons:  

1. Most cited papers were published before 2021 and are included in other reviews on the same topic.

Response: We would like to express our appreciation to the reviewer for their feedback. Our main goal with this narrative review was to provide a comprehensive overview of the most recent and most impactful studies related to the chosen topics. We ensured that all studies included in this review were published after 2018, some as late as 2023. We have provided the date of each study in the new dedicated table.

1. There is no separation of nano- and microplastic. The indication of the sizes, for which the statements apply, is usually missing.

 Response: We would like to thank the reviewer for providing such an insightful clarification. We apologize for the inaccuracy on the issue of particle size, which requires some elucidation. Therefore, we have made the necessary changes to the paper, specifying the above details in the in vitro studies on human cell lines and in vivo studies on animal models, which are the main focus of the review. Regarding the division between micro- and nanoplastics, we have included a table summarizing the reference studies. This will facilitate a complete treatment of the topic covered in the review.

1. What are the specific insights that were gained by specific in vitro and in vivo studies, e.g. how did the invertebrate studies contribute to the gain of knowledge. Are they suitable for the assessment of these particles?

Response: We are grateful for the reviewer's insightful observation. While it is true that the phylogenetic distance between invertebrates and mammals may not provide any unique insights into the studies cited, it is important to note that these references were carefully chosen to provide readers with an understanding of the effects of MNPs on the intestinal system of both types of animals. By including studies on animals from different phyla, we were able to provide a broader perspective that enhances the relevance and significance of our research. We appreciate the opportunity to clarify this point.

1. The difficulty to measure the levels of nano- and microplastic was not addressed but has a great impact on the interpretation of the data.

We would like to thank the reviewer for providing such insightful clarification. We have included our own understanding and analysis of this matter in the concluding remarks.

1. Conflicting data were not discussed, e,g, the microparticle content in fruits and vegetables was reported quite differently and only one publication is cited.

----Response: we would like to thank the reviewer for the comment. We have reformulated the most conflicting aspects in the conclusions. With reference to the cited example, our main goal is to provide an in-depth coverage of the potential adverse effects of MNPs on the intestinal system. We fully agree that going to understand and analyze the true extent of human exposure to these particles through the food chain would represent a breakthrough in future research designs. We have emphasized the concept in the review.

1. The issue of plasticizer is not addressed.

--Response: we would like to thank the reviewer for the interesting suggestion. Plasticizers and microplastics are two distinct molecules, albeit with similar and widespread usage. The topic of pollutants and plasticizers is not central to the goals of the review, but we still wanted to include several comments on that, given the substantial impact they can have on human health.

1. The relevance of the exposure doses/concentrations is not indicated.

Response: We would like to express our gratitude to the reviewer for their comment and offer our apologies for any inaccuracies found in our work. After careful review, we have taken steps to address these issues by including missing data regarding the exposure doses of MNPs from individual studies involving mammals and human cell lines. Additionally, we have included a summary table to provide a clear overview of this information.

However, in some of these studies, giving a detailed view on the multiple concentrations used would cause a deterioration in the readability of the text. Some studies, on the other hand, are repeated in the manuscript, which is why we have not unnecessarily specified the various study details already mentioned.

1. The effects on microbiota are listed – what is the relevance?

--Response: we would like to thank the reviewer for the question. The scientific community has been exploring the role of gut microbiota in the intestinal system and its potential impact on the development and treatment of various diseases. It is crucial to further investigate the potential effects of micro- and nanoplastics on this microbial system, as it could provide valuable insights for future scientific research. By focusing on this area, we can better understand the potential risks of plastic waste on human health, and work towards developing more effective strategies to mitigate any negative impacts.

Typing error:

--l.250: piristine

Response: We thank the reviewer for the comment. We modified it as suggested.

Reviewer 3 Report

The review is interesting. The toxicological effects of the micro- and nanoplastics have been reviewed. However, some issues need to be changed before publication. The redaction talks about micro and nano particles, the vision of the article in general does not go deep into the chosen topic. It only lays a foundation already well described in many previous publications.

There is a lack of explanatory figures that add something to the information already published. Perhaps one summarizing the effects described throughout the works.

One or more summary tables would also help to improve the work.

The tittle of the manuscript is subscribing the effects of particles in the humans, and their effects on de microbiota, but the mayor part of the text is focused in the studies in mammals and the works published in the digestive system. Being the discussion about microbiota so limited, a change in the tittle should be desirable.

The studies that are cited in the work are related to artificial microplastics, natural microplastics, a few related to contaminants… Could be interesting a table with the works, micro- o nano-, concentrations, artificial or manufactured, mammals fish or invertebrates… etc.?

Specific comments

Line 111: In the toxicological mechanisms of MNPs, the attachment of toxicants is not considered? Although is mentioned in the next section, it could be mentioned.

Line 143: Only German beer?

Line 282: There are recent studies on fish about the effects of MPs and NPs and toxicants on the immune system and gut structure. Even a transcriptomic study on D labrax.

Line 336: The title of the manuscript says: “in humans” and in the corresponding section one of the first comment speak about the lack of data. If the review speak about mammals, then is in mammals. Again, ai suggest to change the tittle.

Author Response

Dear editorial assistant and reviewers,

sincerely grateful for the invitation received for the writing of this manuscript, we have made the content changes requested by the reviewers. Below are the clarifications and responses to the comments made by the reviewers.

Reviewer #3

The review is interesting. The toxicological effects of the micro- and nanoplastics have been reviewed. However, some issues need to be changed before publication. The redaction talks about micro and nano particles, the vision of the article in general does not go deep into the chosen topic. It only lays a foundation already well described in many previous publications.

Response: We are grateful for the constructive criticism provided and have made significant revisions to various sections of the document. We trust that these changes have addressed the highlighted concerns and have refined the overall quality of the document.

--There is a lack of explanatory figures that add something to the information already published. Perhaps one summarizing the effects described throughout the works.

One or more summary tables would also help to improve the work.

Response: We thank the reviewer for the interesting suggestion. We have included an explanatory figure and a table in the review.

--The title of the manuscript is subscribing the effects of particles in the humans, and their effects on de microbiota, but the mayor part of the text is focused in the studies in mammals and the works published in the digestive system. Being the discussion about microbiota so limited, a change in the tittle should be desirable.

Response: We thank the reviewer for the interesting suggestion. We have revised the title of the paper to make it more relevant to the topic.

--The studies that are cited in the work are related to artificial microplastics, natural microplastics, a few related to contaminants… Could be interesting a table with the works, micro- o nano-, concentrations, artificial or manufactured, mammals fish or invertebrates… etc.?

Response: We thank the reviewer for the interesting suggestion. We have included an explanatory figure and a table in the review.

Specific comments

--Line 111: In the toxicological mechanisms of MNPs, the attachment of toxicants is not considered? Although is mentioned in the next section, it could be mentioned.

Response: We would like to thank the reviewer for the clarification. Plasticizers, pollutants and microplastics are distinct molecules, albeit with similar and widespread usage. The topic of pollutants and plasticizers toxicity is not central to the goals of the review, but we still wanted to include several comments on that, given the substantial impact they can have on human health.

--Line 143: Only German beer?

Response: In the article cited about 24 brands of German beers was analyzed for microplastic content, and in all cases contamination was found. Because these beers may have production facilities other than Germany, we simplified to 'beer'. 

--Line 282: There are recent studies on fish about the effects of MPs and NPs and toxicants on the immune system and gut structure. Even a transcriptomic study on D labrax.

Response: we would like to thank the reviewer for the interesting proposal. We agree that these studies including the one mentioned above can contribute to future research on the topic. The fish studies have primarily contributed to our understanding of how these microplastics can contaminate environments, wildlife, and the food chain. Second, these studies have given us initial hints about the possible effects of micro- and nanoplastics on the intestinal system, albeit of a different nature than in mammals. For these reasons, we wanted to include references to this topic in our review, although it is not the main focus of the paper.

--Line 336: The title of the manuscript says: “in humans” and in the corresponding section one of the first comment speak about the lack of data. If the review speak about mammals, then is in mammals. Again, ai suggest to change the tittle.

Response: 

We are grateful for the reviewer's insightful suggestion, which prompted us to reconsider the title of our paper. As a result, we have revised the title to better capture the essence of our research, and we believe this change will make the paper even more compelling and impactful. We decided to rename the title as follows: “micronanoplastics and their potential impact on human gut health: a narrative review”. We understood the concerns about 'in humans'. In this new version of the title, we have incorporated the term "potential" to acknowledge the current level of uncertainty surrounding the evidence on the subject. Studies in mammals and human cell lines provides us with a comprehensive basis for understanding the possible adverse effects of the issue in humans. We have further emphasized these findings in the conclusions section. Thank you for helping us improve the quality of our work.

Round 2

Reviewer 2 Report

The authors addressed my comments.

Author Response

We would like to thank the reviewer for the important suggestions provided.

Reviewer 3 Report

In general, the manuscript has been upload with the suggested changes.

Some minor errors (such as typing error) should be revised. (for example line 477)

If the units are mg mL^-1 or mg/mL. Please homogenize the format along the manuscript

Author Response

We apologize for the inaccuracies found. We have edited and standardized the units of measurement indicated.

We would like to thank the reviewer for the important suggestions provided.