Microplastics Dynamics in the Bathing Seawater Affected by the Ebb Tide in Zhanjiang Bay, China

Round 1

Reviewer 1 Report

The authors monitor the spatial and temporal distribution and composition of MPs considering the ebb tide of an important bay in south China, in addition to assessing the effects of human activities and tides on MPs inside and outside the bathing area. The topic is important for conducting an environmental risk assessment for environmental contaminants, including MPs. Overall, the manuscript met the journal's requirements, the writing is clear and easy to follow. The manuscript presents an easy-to-follow methodology, results, and discussion. After careful consideration, I have reached the decision that the manuscript is acceptable for publication in its current form.

Author Response

 Thank you very much for considering this manuscript for publication.

Reviewer 2 Report

This paper reports the distribution of microplastic particles in a beach, highlighting the effects of tide on their accumulation. The aims of the study are clearly defined and the experimental setup is generally well-conceived. However, authors should more clearly state some methodological setup and should improve the discussion and presentation of results before the publication of this manuscript in my opinion.

Firstly, considering methods, QA-QC protocols need to be clearly stated and are needed for a good validation of data (see for example Lu et al. 2021 https://doi.org/10.1016/j.scitotenv.2021.146693 ). For example, were procedural or field blanks analyzed?

Moreover, some details on sampling strategy are not clear to me. From lines 115-118, it is not clear how much water was collected and in which time frame. It should be also stated at which depth (e.g., surface or along the water column) water was collected, since this can affect the results.

Then, authors should improve the presentation of results, and indicate why they selected specific analysis and comparison. Firstly, why did authors test only the relationships between plastic sizes and abundance in section 3.3? What about different polymer types? The authors mentioned the analytical approach with FT-IR but this is not discussed in text.

Moreover, do the authors consider other factors affecting transport of floating plastic? For example, main winds and currents should be mentioned, as well as local sources from the beach (see e.g. Bellasi et al., 2022 , https://doi.org/10.3390/app12115388 ).

Then, discussion of the paper should be strongly revised. As it is, the discussion is pretty general and indicates the main trends related with general monitoring of microplastic in sea with different sampling systems (especially in sections 4.1, 4.3 and 4.4). Authors should instead focus more the discussion in comparison with their data and crafting it more in function of the aims of the study. Authors for example, should better discuss the possible hypothesis of different spatial distribution of plastics in different tidal phases, which is only listed in lines 298-301). As an example, authors can see Cai et al., 2018 https://doi.org/10.1016/j.scitotenv.2018.03.197 .

There are then some minor issues to revise:

-lines 68-79: This section can be shortened and some information can be moved in the study area section.

-line 133: what type of spectrophotometer was used? A micro FT-IR? Authors should state this detail.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The paper entitled “Microplastics dynamics in the bathing seawater affected by the ebb tide in Zhanjiang Bay, China” tackles an essential and interesting topic with a high level of novelty. However, due to its drawbacks, it should be revised before its publication. In particular:

-         The method of sampling and identification should be mentioned in the abstract,

-         Units should be with “-“ power not “/” (e.g. items · kg^-1)

-         Line 28-67 can be skipped (too general and obvious, please concentrate on the main aspect) and changed for the concise introduction stressing the main points (stated in line 59-60 and line 65-67)

-         Any more specific information about local tides and currents? (lines 68-79)

-         The objectives are not “variations” (1, 3 and 4) but “checking variations” or “confirming variations”, studying, etc

-         Lines 95- 106, please rephrase to make it more scientific and limited to facts, data

-         Lack of space between reference numbers [45, 46]

-         It is not enough to state it like this: 113 modified beach sampling procedures and standardized methods and their details have

-         114 has been previously published [45,46]. – at least critical points of the protocol should be shown in the paper

-         Line 125: it should be repeated in the discussion/conclusions as the lower fraction will have the highest mobility and create the most significant difference due to tide

-         Table 1 can be placed in supplementary material

-         Lines 138-149, in what way the changeable weather conditions and roughness of the sea/waves are included here? Some estimations of the errors due to wave occurrence?

-         Have You checked the Gaussian distribution of Your data before using ANOVA?

-         How did You identify and detect MPs, and what was the accuracy of Your estimations?

-         Lines 176-179: Did You correct the results by the differences in identification accuracy?

-         Spaces before the mm are missing

-         What is the polymer composition of those MPs?

-         How many/what % of debris were excluded as no-polymer origin?

-         Lines 235-240: to what extent did You consider the differences in sampling protocols before comparing the data?

-         I do not feel that conclusions are justified by the results: there are too little data to draw it in such a general way

All in all, I suggest a major revision.

With regards,

Reviewer

Author Response

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Round 2

Reviewer 2 Report

The revised version of the paper clearly improved in term of presentation quality. There are still few minor issues to revise before its publication in my opinion:

-line 33: "enter" instead of "entering";

-line 120: is it 20 ml of each solution? or 20ml of the mixture? Moreover, which was the Fe(II) concentration? Please add those details;

-lines 319-320: unclear sentence, please rephrase it;

-lines 344-345: please rephrase to avoid the repetition of "scenic area".

Author Response

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Reviewer 3 Report

Thank You for addressing all comments. In my opinion, this paper can be accepted for publication. Some minor spell-chek needed.

Reviewer

Author Response

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