Unveiling Microplastic Abundance and Distribution in an Oceanic Island: Offshore Depository or Local Pollution Indicator

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study revealed an important local MP source from an apparently pristine touristic region which, aligned with other recent findings, unveils an important and silent pollution issue, potentially affecting oceanic islands, that should be seriously addressed in future studies and raise concern on litter management and mitigation and environmental awareness actions. The paper as a whole is acceptable for publication after following corrections:

1 In the text, the authors use "fiber" to describe the shape of plastics. It should be corrected by using another word, such as "strip", because "fiber" refers to a synthetic material which doesn't belong to plastics.

2 About the local actions to prevent plastic pollution, the author should mention what has already been or planned to be carried out at present, since not all the proposed actions are needed to be done from the beginning.

3 The authors are encouraged to identify the site with most serious plastic pollution, so as to put it as the priority.

Author Response

This study revealed an important local MP source from an apparently pristine touristic region which, aligned with other recent findings, unveils an important and silent pollution issue, potentially affecting oceanic islands, that should be seriously addressed in future studies and raise concern on litter management and mitigation and environmental awareness actions. The paper as a whole is acceptable for publication after following corrections:

1 In the text, the authors use "fiber" to describe the shape of plastics. It should be corrected by using another word, such as "strip", because "fiber" refers to a synthetic material which doesn't belong to plastics.

Response: Although we understand the reviewer perspective, we decided to use “fibre” since, as far as we know, all articles focusing microplastics categories use the same word, thus maintaining the same terms in similar studies.

 

2 About the local actions to prevent plastic pollution, the author should mention what has already been or planned to be carried out at present, since not all the proposed actions are needed to be done from the beginning.

Response: Done

 

3 The authors are encouraged to identify the site with most serious plastic pollution, so as to put it as the priority.

Response: Done

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

I read your manuscript with interest and find it contributing to the global understanding of the distribution and transformation of microplastics in the environment. At the same time, I believe that some of the important problems that you raised were discussed superficially. They are as follows:

/1/ It is not clear how the spread of microplastics and their forms relates to the spread of human settlements on the island. Neither a map of settlements nor a map of population density on the island is provided. These maps could provide a better understanding of the reasons for the abundance of microplastics in the island's coastal zone. This is a significant flaw in the manuscript. It is also unclear in the manuscript why the distance from the sampling points to the nearest settlements was calculated along a straight line, and not along the contours of the hydrographic network along which the bulk of microplastics move. Moreover, settlements differ in numbers, industrial specialization, etc. Consequently, their contribution as sources of microplastics is different. All these issues need to be discussed in more detail in the manuscript.

/2/ The relationship between the abundance/forms of microplastics and the sediment texture in which they are found is also superficially revealed. This is an important question, which also allows us to conclude both the origin of microplastics and their transportation and preservation in the environment.

/3/ You briefly wrote that sea cruise tourism in the waters of Macaronesia also contributes to microplastic pollution of the marine environment and the environment in the coastal zone of local islands. It would be highly desirable if you examined this issue in more detail in your manuscript, drawing on the research of other authors in this part of the Atlantic. After all, this is also a source of microplastics in the coastal zone of the studied island!

Comments on the Quality of English Language

The quality of English is generally good and minor improvements are needed.

Author Response

Dear Authors,

I read your manuscript with interest and find it contributing to the global understanding of the distribution and transformation of microplastics in the environment. At the same time, I believe that some of the important problems that you raised were discussed superficially. They are as follows:

/1/ It is not clear how the spread of microplastics and their forms relates to the spread of human settlements on the island. Neither a map of settlements nor a map of population density on the island is provided. These maps could provide a better understanding of the reasons for the abundance of microplastics in the island's coastal zone. This is a significant flaw in the manuscript. It is also unclear in the manuscript why the distance from the sampling points to the nearest settlements was calculated along a straight line, and not along the contours of the hydrographic network along which the bulk of microplastics move. Moreover, settlements differ in numbers, industrial specialization, etc. Consequently, their contribution as sources of microplastics is different. All these issues need to be discussed in more detail in the manuscript.

Response: Done, and a map of population density was added and discussed.

 

 

/2/ The relationship between the abundance/forms of microplastics and the sediment texture in which they are found is also superficially revealed. This is an important question, which also allows us to conclude both the origin of microplastics and their transportation and preservation in the environment.

Response: Done, although there is not much more in the bibliography regarding this issue.

 

/3/ You briefly wrote that sea cruise tourism in the waters of Macaronesia also contributes to microplastic pollution of the marine environment and the environment in the coastal zone of local islands. It would be highly desirable if you examined this issue in more detail in your manuscript, drawing on the research of other authors in this part of the Atlantic. After all, this is also a source of microplastics in the coastal zone of the studied island!

Response: Done, this issue is examined in more detail.

Reviewer 3 Report

Comments and Suggestions for Authors

Your study on the distribution of microplastics around an oceanic island provides valuable insights, and I commend you for your excellent work. The major concern is that besides the measurement you provide, what in-depth analysis you can inform the research community.  Additionally, I'd like to offer some minor adjustments for your consideration:

Regarding the title, it seems that the focus is primarily on measuring the abundance of microplastics rather than investigating their origins. Could you please refine the title to reflect this focus more accurately?

On line 79, the acronym PVC is used without prior introduction. For clarity, please introduce the full term before using the acronym.

The discussion on lines 92-97 appears unrelated to the study's main focus, as it ventures into biological perspectives not explored within your research. Consider revising or omitting this section for better alignment with your study's objectives.

In lines 101-110, elaborating on the significance of your study area and discussing how your findings might be generalized or contribute to understanding global patterns would greatly benefit the reader. Could you elaborate on this aspect?

On line 105, please adjust the notation for square meters to "m²" for consistency.

For Figure 1, a higher resolution would enhance its interpretability. Would you mind updating it?

On line 143, if "UW" refers to sediment, using "sediment" might be clearer and more widely recognized. Could you please clarify?

Line 229 seems to refer ambiguously to islands and beaches. Could you specify the context more clearly?

On line 234, providing details on your detection limits and the methods used for characterization would enhance the reader's understanding. Could you include this information?

The term "total" in Figure 2 is a bit unclear. Do you mean the average size in total? Clarification here would be helpful.

In Figure 3, the rationale for the specific directional categorization (west, north, east, south) is not clear. Could you provide further explanation?

For line 346, the notation for inverse meters should be corrected to "m⁻¹" for consistency.

On line 397, incorporating references for airborne transport to recent publications could offer additional context and relevance. Would you mind updating your citations?

Xiao, S., Cui, Y., Brahney, J., Mahowald, N.M. and Li, Q., 2023. Long-distance atmospheric transport of microplastic fibres influenced by their shapes. Nature Geoscience, 16(10), pp.863-870.

 

By line 422, a more explicit mention of the methodologies used for characterization would aid in comprehending your approach.

On line 439, elucidating the reasons why storms might transport denser microplastics to your study area could add depth to your discussions.

Lastly, any insights on potential sources of the microplastics, as mentioned on line 514, would indeed be valuable. Identification of sources could significantly enhance the study's impact.

I appreciate your attention to these suggestions and look forward to seeing your refined work, which no doubt contributes meaningfully to our collective understanding of environmental sciences.

Author Response

Your study on the distribution of microplastics around an oceanic island provides valuable insights, and I commend you for your excellent work. The major concern is that besides the measurement you provide, what in-depth analysis you can inform the research community.  Additionally, I'd like to offer some minor adjustments for your consideration:

Regarding the title, it seems that the focus is primarily on measuring the abundance of microplastics rather than investigating their origins. Could you please refine the title to reflect this focus more accurately?

Response: Done

 

On line 79, the acronym PVC is used without prior introduction. For clarity, please introduce the full term before using the acronym.

Response: Done

 

The discussion on lines 92-97 appears unrelated to the study's main focus, as it ventures into biological perspectives not explored within your research. Consider revising or omitting this section for better alignment with your study's objectives.

Response: Done it was deleted.

 

In lines 101-110, elaborating on the significance of your study area and discussing how your findings might be generalized or contribute to understanding global patterns would greatly benefit the reader. Could you elaborate on this aspect?

Response: Done

 

On line 105, please adjust the notation for square meters to "m²" for consistency.

Response: Done

 

For Figure 1, a higher resolution would enhance its interpretability. Would you mind updating it? Response: Done

On line 143, if "UW" refers to sediment, using "sediment" might be clearer and more widely recognized. Could you please clarify?

Response: Clarified.

 

Line 229 seems to refer ambiguously to islands and beaches. Could you specify the context more clearly?

Response: Done

 

On line 234, providing details on your detection limits and the methods used for characterization would enhance the reader's understanding. Could you include this information?

Response: Done

 

The term "total" in Figure 2 is a bit unclear. Do you mean the average size in total? Clarification here would be helpful.

Response: Done

 

In Figure 3, the rationale for the specific directional categorization (west, north, east, south) is not clear. Could you provide further explanation?

Response: Done

 

For line 346, the notation for inverse meters should be corrected to "m⁻¹" for consistency. Response: Done

 

On line 397, incorporating references for airborne transport to recent publications could offer additional context and relevance. Would you mind updating your citations?

Response: Done  

 

By line 422, a more explicit mention of the methodologies used for characterization would aid in comprehending your approach.

Response: Done

 

On line 439, elucidating the reasons why storms might transport denser microplastics to your study area could add depth to your discussions.

Response: Done

 

Lastly, any insights on potential sources of the microplastics, as mentioned on line 514, would indeed be valuable. Identification of sources could significantly enhance the study's impact.

Response: Done

Reviewer 4 Report

Comments and Suggestions for Authors

Dear Authors

The article concerns current problems related to the occurrence of microplastics in the environment. The authors conducted detailed research on the island of São Miguel, which concerned:

1) estimate the abundance, category, and dimension of MP along the coast of São Miguel Island, following an inshore-offshore gradient from a stream to the ocean;

2) identify the categories of MP detected;

3) identify and discuss the differences and factors that may contribute to its distribution.

The results presented in the work seem to be interesting and reliable, but the most important achievements were not adequately presented in the conclusions chapter. Before publishing the manuscript, the authors should correct the conclusions section so that they refer to the study aims. It is necessary to indicate the most important achievements resulting from the research conducted.

Author Response

Dear Authors

The article concerns current problems related to the occurrence of microplastics in the environment. The authors conducted detailed research on the island of São Miguel, which concerned:

1) estimate the abundance, category, and dimension of MP along the coast of São Miguel Island, following an inshore-offshore gradient from a stream to the ocean;

2) identify the categories of MP detected;

3) identify and discuss the differences and factors that may contribute to its distribution.

The results presented in the work seem to be interesting and reliable, but the most important achievements were not adequately presented in the conclusions chapter. Before publishing the manuscript, the authors should correct the conclusions section so that they refer to the study aims. It is necessary to indicate the most important achievements resulting from the research conducted.

Response: Done, conclusions were clarified.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I did not receive convincing answers to my comments 2 and 3.

I admit that no one has directly analyzed the relationship between sediment granulometry and plastic content in the Azores. However, these issues were probably dealt with in other regions of the planet. Try to adapt these results to the study island.

In the manuscript, I also did not find a convincing analysis of the impact of cruise ships on microplastics. Please try to analyze other regions of the world with similar problems, where these issues have been more-less resolved, and make at least calculations and forecasts for the island of St. Miguel.

Comments on the Quality of English Language

Minor editing of English language required

Author Response

All suggestions were incorporated in agreement with the suggestions. Thank you

Reviewer 3 Report

Comments and Suggestions for Authors

Accept in present form

Author Response

All changes were made in agreement with the suggestions. Thank you

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

The authors took my comments into account.

Please, check out this paper that was published recently: https://www.mdpi.com/2076-3298/11/4/83

It may be of interest to you for your future research.

Comments on the Quality of English Language

Minor editing of English language required