Microplastic Pollution in Tropical River: Fourier Transform Infrared Spectroscopy-Based Characterization of Abundance and Polymer Composition in Water and Sediments from Filobobos River, Mexico

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

General comments: This study focuses on the retention and characteristics of microplastics (MPs) in the waters and sediments of the Bobos River lower basin in Mexico, and analyzes their distribution in combination with hydrodynamic and human activities (citrus industry). Unfortunately, the manuscript is not currently ready for publication and needs to be revised.

Specific comments:

1. MPs is not defined in the abstract, it is recommended to write the full name.
2. The research results in the abstract are descriptive and there are no conclusions of special significance.
3. The distribution description of sample sites is not clear enough. Is the entire basin on the map surveyed? Why is there no multiple relationship between water samples and sediment samples? The relationship between the two is not clearly defined.
4. The methodological part is not well described. Lines 92-94 should appear in the Methods section.
5. line 100-101, Place of origin, manufacturer and model should be expanded in brackets.
6. line 124, "in addition to incorporating iron (Fe2+) as a catalyst," what are the reasons?
7. line 133, "using a (4X) method.....", Lack of specific information. In addition, there is a lack of instruments and methods in section 2.4.
8. line 156, Is the sampling done all at once? Why is there such a big temperature difference.
9. line 160-161, This information belongs to the methodology section.
10. Part 3.3 is not rigorous enough. First of all, the classification of substances requires standard spectra and detection spectra. So it needs to be shown at the same time, and it needs to be clear what the fit of the spectrum is. Secondly, the author only shows PE and PET, are there other categories? What are the respective percentages?
11. Table 3 is recommended as supplementary material.
12. There is a biggest problem in this manuscript, that is, the relevant indicators of hydrology are hardly measured, but the results are obtained by summarizing a large number of literatures in the discussion section. This means that previous measurements are meaningless. The author said in the introduction that the deposition of microplastics is affected by multiple factors such as water flow speed, discharge, and channel structure, but these relevant data have not been measured, so conclusions of manuscript can not be drawn. The author measured some water quality indexes and physical and chemical indexes of water body. I suggest the author analyze the relationship between these indexes and microplastics of water body, and further analyze the sediment microplastics. The source analysis of microplastics was carried out to obtain the influence of human activities on the accumulation of microplastics.

Author Response

Dear reviewer, please refer to the attached file. Thank you.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript is well written, it is subjected to some improvement before being accepted for publication:

1. Section 1. Paragraph 1, the current description lacks the major environmental concerns related to the plastic pollution to aquatic system, which should be supported with recent published papers.
2. Section 2.2, Line # 82, author should provide a table of details of 9 samples, which contain sample ID, location, coordinates etc.
3. Section 2.2.1 Line # 94, which standard method of water sampling was followed?
4. Table 3, why is there only 1 data for sample ID SA4?
5. Figure 10, font six=ze and graph line should be consistent with other figures.
6. Line # 73-74, km2 to km² and 3,200 meters to 3,200 m, and check for other sections of manuscript.
7. Line # 28, full form of MPs should be provided and check for other sections of manuscript.

Author Response

Dear reviewer, please refer to the attached file. Thank you.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This study is interesting since it presents water and sediment microplastic characteristics in the Bosbos River in Mexico. It analyzed microplastics retention and characterization in the Bobos River, considering their interaction with flow regimes and relating it to citrus activities in the region. However, the introduction is too short. The research gap is missing in the introduction. There are many studies about microplastics, but what is new about this study? Are the generated new information highly beneficial for the region? Give pieces of evidence by citing relevant related references. These must be added in the introduction.

Page 2 Line 49 – 50: what do you mean with Rivers are dynamic systems where hydrology and human activity determine pollutants 37 mobility and retention.

Figure 2 – where is the location of the citrus agroindustry? It must be included in the map since this seem to be the novelty of the study.

Section 2.2.1 – when was the sampling conducted? Which month and season? This information is essential because it will give the readers a background about the likelihood of the microplastics trend. Usually, there are higher MPs during the wet season than the dry season. Similarly, the dominant shapes vary during the season.

Table 2 – What is NT? I think this parameter was not defined. Is CE same with EC?

Figure 9 and 7 has incorrect spelling of Transparent

Why were there only two types of polymers identified? Is this a limitation of the study? Because this was not mentioned in the paper.

Did the study validate the MP sources from the citrus industry? Because this was not mentioned in the conclusion.

The grammar in the discussion, especially section 4.1 must be improved.

Author Response

Dear reviewer, please refer to the attached file. Thank you.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The author's revised manuscript has addressed most of my concerns, but the author seems to have been avoiding the issue of microplastic category identification all along. As the author mentioned, a total of 96 microplastics were discovered. So, are all the categories PE or PET? No other categories?

Author Response

Dear Reviewer, the response is included in the attached document. I appreciate your comments and corrections.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have revised accordingly 

Author Response

Dear Reviewer, I sincerely appreciate all your comments and suggested improvements. Thank you in advance.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors addressed all of my comments and suggestions. I recommend acceptance of the manuscript for publication.

Author Response

Dear Reviewer, I sincerely appreciate all your comments and suggested improvements. Thank you in advance.