Investigation of Microplastics in Surface Water and Estuarine Mullet Mugil cephalus from 23 Estuary Areas, South China

Round 1

Reviewer 1 Report

The current manuscript entitled “Investigation of Microplastics in Surface Water and Estuarine Mullet Mugil Cephalus from 23 Estuary Areas, south China” by Zhang et al. provided an extensive amount of data on the presence and impact of microplastics in these estuaries. The data presented in the manuscript is comprehensive and clear, and the authors have done an excellent job of analyzing the data collected. In particular, the authors have conducted an effective analysis of the size and composition of microplastics present in the estuaries. Additionally, the authors have provided an in-depth discussion of the implications of their findings in terms of the potential environmental and human health risks posed by microplastics. I suggest acceptance of this manuscript pending a suitable minor revision. My specific comments are:

1.      Line 2: Delete “The investigation data is in the supplementary”.

2.      Add brief methods used for microplastic analysis and categorization in the abstract.

3.      Major numerical results are missing from the abstract.

4.      The reference formatting should be corrected as per MDPI style.

5.      Introduction line 2: delete (2023.1).

6.      Add the scientific authority of Mugil cephalus.

7.      Improve the histogram and text color (pure black) in all bar charts.

8.      Correct the syntax and grammatical errors in the whole paper.

Author Response

Response to Reviewer 1

Thank you for your comments and suggestions for our manuscript. We have found that your comments are very constructive and helpful to improve quality of the manuscript. The manuscript has been revised according to your suggestions. Below you will find our point-by-point responses. We hope that the revised paper will meet your standard for the journal.

1. Line 2: Delete “The investigation data is in the supplementary”.

Thanks for your suggestion. We have deleted the sentence.

2. Add brief methods used for microplastic analysis and categorization in the abstract.

Thanks for your suggestion. We have added the brief methods, please see line 16-17.

3. Major numerical results are missing from the abstract.

Thanks for your suggestion. Major numerical results have been shown in the abstract. The average abundance of microplastics was 18,261 items/m³ in the surface water, and 7.2 items/individual in fish (line 17-19). Fragments and minute sized particles were the most common features found in both the water and the fish samples (line 20-21).

4. The reference formatting should be corrected as per MDPI style.

Thanks for your suggestion. We have corrected the reference formatting in the revised manuscript.

5. Introduction line 2: delete (2023.1).

Thanks for your suggestion. We have deleted the date.

6. Add the scientific authority of Mugil cephalus.

Thanks for your suggestion. The mullet Mugil cephalus is a kind of demersal fish with a wide range of habitats. M. cephalus is commonly found in fresh water, brackish water, and in marine environments. Tolerance to a wide range of salinities is to the hallmark of the observed global success of mullet as a species. As an omnivorous fish, mullet is potentially in danger of ingesting pollutants and microplastics, lending to its utility for ecotoxicological studies. Please see line 43-47.

7. Improve the histogram and text color (pure black) in all bar charts.

Thanks for your suggestion. We have improved the histogram.

8. Correct the syntax and grammatical errors in the whole paper.

Thanks for your suggestion. This manuscript had been edited by the International Science Editing. 

Reviewer 2 Report

This study investigated the level of microplastics in surface water and estuarine mullet Mugil cephalus from 23 estuary areas in the south of China. According to the authors, the average abundance was 18,261 items/m3 in the surface water and 7.2 items/individual in fish. The study revealed significant pollution due to microplastics in the environment. Fragments and minute sized particles were the most common features found in both the water and fish samples. Some impurities in the water sample were easily confused with microplastics, but regular forms on the surface of the impurity could be distinguished by using scanning electron microscopy. The shape, color, and size of the microplastics were similar, suggesting that they could enter organisms' bodies and affect the health of aquatic species and humans. The authors recommend that monitoring and managing of microplastics be addressed in the estuaries.

My observations are listed below:

1.     Some superfluous and ambiguous sentences can be found in the Abstract and the body of the paper. For example "The investigation data is in the supplementary." I advise having a professional who is a native English speaker conduct a thorough review.

2.     The figures' format is dated. Please swap them out for more modern styles. If necessary, seek assistance from a qualified illustrator or designer.

3.     Rest is fine.

 

Author Response

Response to Reviewer 2

 

Thank you for your comments and suggestions for our manuscript. We have found that your comments are very constructive and helpful to improve quality of the manuscript. The manuscript has been revised according to your suggestions. Below you will find our point-by-point responses. We hope that the revised paper will meet your standard for the journal.

1. Some superfluous and ambiguous sentences can be found in the Abstract and the body of the paper. For example "The investigation data is in the supplementary." I advise having a professional who is a native English speaker conduct a thorough review.

Thanks for your suggestion. This manuscript had been edited by the International Science Editing. 

2. The figures' format is dated. Please swap them out for more modern styles. If necessary, seek assistance from a qualified illustrator or designer.

Thanks for your suggestion. We have improved the figures' format.

Reviewer 3 Report

 

Investigation of microplastics in surface water and estuarine mullet Mugil cephalus from 23 estuary areas, south China:

·        In the last paragraph of the Introduction, the authors should mention the weak point of former works (identification of the gaps) and describe the novelties of the current investigation to justify that the paper deserves to be published in this journal.

·        Discuss more the characteristics and distribution of microplastics in estuarine mullet Mugil cephalus.

·        Focus on the sustainability aspect of your study.

·        Discuss the most important reasons for the variations of the Distribution of microplastics in estuarine mullet Mugil cephalus from 23 estuary areas.

·        Focus on the advantages/disadvantages of the proposed method concerning the obtained results.

·        It is necessary to explain the sources of error in this study to consider them in the next investigations.

·        At the end of the manuscript, explain the implications and future works considering the outputs of the current study.

·        The quality of the language needs to be improved for grammatical style and word use.

Author Response

Response to Reviewer 3

Thank you for your comments and suggestions for our manuscript. We have found that your comments are very constructive and helpful to improve quality of the manuscript. The manuscript has been revised according to your suggestions. Below you will find our point-by-point responses. We hope that the revised paper will meet your standard for the journal.

 

1. In the last paragraph of the Introduction, the authors should mention the weak point of former works (identification of the gaps) and describe the novelties of the current investigation to justify that the paper deserves to be published in this journal.

Thanks for your suggestion. The locations of the two investigations were different. In a previous study, we investigated pollution by microplastics in the surface water from the eastern coastal areas of Guangdong, south China. In the present study, we investigated pollution by microplastics in the surface water from the west of Guangdong Province. The research areas involved four cities: Jiangmen, Yangjiang, Maoming and Zhanjiang (located in the southernmost part of mainland China), which filled in the location gap in the previous study. Please see line 75-76.

2. Discuss more the characteristics and distribution of microplastics in estuarine mullet Mugil cephalus.

Thanks for your suggestion. We have added the supplements in line 308-317.

3. Focus on the sustainability aspect of your study.

Thanks for your suggestion. We had added the supplements about sustainability of plastics and fish health, please see line 283-285 and 333-338.

4. Discuss the most important reasons for the variations of the Distribution of microplastics in estuarine mullet Mugil cephalus from 23 estuary areas.

Thanks for your suggestion. We have added the supplements in line 291-304.

5. Focus on the advantages/disadvantages of the proposed method concerning the obtained results.

Thanks for your suggestion. In the method, scanning electron microscopy (SEM) was used to get high-definition images of microplastics, which had higher definition than traditional single microscope. Some impurities in the water sample were easily confused with microplastics, but regular forms on the surface of the impurity could be distinguished by using SEM. However, the chosen particles should be placed on double-sided tape and coated with evaporated gold before SEM observation, which were hard for operation. We have added the supplements in line 146-148.

6. It is necessary to explain the sources of error in this study to consider them in the next investigations

Thanks for your suggestion. The surface of the microplastic was uneven, which might create conditions for the adsorption of other pollutants. Some impurities in the water sample were easily confused with microplastics, but regular forms on the surface of the impurity could be distinguished by using SEM. We have added the supplements in line 175 and 181.

7. At the end of the manuscript, explain the implications and future works considering the outputs of the current study.

Thanks for your suggestion. The study revealed serious miroplastics contamination of water and commercial fish in estuarine systems, and sounded the alarm for the supervision and governance of plastic wastes. Future work should focus on the risk of microplastics contaminants being passed down the food chain to humans. We have added the supplements in line 345-348.

8. The quality of the language needs to be improved for grammatical style and word use.

Thanks for your suggestion. This manuscript had been edited by the International Science Editing. 

Round 2

Reviewer 2 Report

Thanks. I'm satisfied.

Reviewer 3 Report

Acceptable in the current form.