Microplastic Occurrence Characteristics and Ecological Risk Assessment of Urban River in Cold Regions during Ice-Covered Periods

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Suggestion:

1, It is better to give the weather condition when sampling.

2,   "line 326-328" concerns about metal ions adoption, it is a little bit misunderstanding. The author showed some common element and heavy metal ions on the surface on MPs. What reasons? originated or adsorbed?

3, The paper needs language writing modification.

4, The list style of literature shall be consistent.

Comments on the Quality of English Language

good. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Introduction

At the end of this section, the authors can describe the research significance of the article to make the structure more complete. Meanwhile, there are still problems that need to be corrected further.

 

L42, the statement that the annual output of plastic products has reached 367 million tons needs to cite references.

 

Materials and methods

The authors' method is basically the same as that of the published studies, so I think the author's method is generally OK. The following part maintains few minor problems that should be modified.

 

Line 119, there are errors in punctuation.

 

Line 179, the word “abundance” and “concentration” should have the same meaning, and frequently use “abundance”.

 

Results and discussion

In this section, the logical relationships of small portions need to be realigned.  Meanwhile, The following part maintains few minor problems that should be modified.

 

L382, This sentence should be changed to “fish pond and other agricultural production area around the sample point”, and the authors should pay attention to the use of conjunctions.

 

L448-L453, The logical relationships in this section are muddled, and the authors are advised to rework the content to accurately express the main idea.

 

L454, Incorrect use of causality here. In other words, the word “therefore” is not used appropriately.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The article describes the occurrence and level of microplastics (MP) pollution in the ice and water of urban inland rivers. The ecological risk assessment results showed that MPS pollution in the Harbin section of the Songhua River reached moderate and severe levels during ice-covered periods. The authors believe that more attention should be paid to potential risks and their control should be strengthened. The article is interesting and increases knowledge in the discussed field. However, before publication, authors must make corrections:

·        Introduction: Insufficient introduction. Please add information in which environmental matrices microplastics are detected and describe in more detail the potential negative impact on living organisms and people.

·        Figure 1 - Please improve the quality of Figure 1

·        2.2 Sample collection and MPs extraction - On what basis did the authors choose the sampling site?

·        3.1. Abundance of MPs in ice and water of mainstream Songhua River - Missing introduction to Figure 2, which should come before Figure. Next, the description of the Drawing and the results is laconic and requires improvement.

·        Figure 3 - Please improve the quality of Figure 3

·        Figure 4 - Please improve the quality of Figure 4

·        Figure 6 - Please improve the quality of Figure 6C

^·             Table 2 – use superscript. Replace „10-3” with 10^-3

·        Figure.A1 - the description of the xy axis and the legend are not visible in the Figure

·        Line 431 – replace „[37],Later” with [37]. Later

·        Table 3. „Pollution Load Index （PLI)”- Move the beginning of the bracket to the next line

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Significance of the Study:

The study on the pollution status of microplastics during the freezing period is intriguing. The author notes its importance for the economic development and residents' health in Harbin. It would be beneficial for the author to provide more specific details on how understanding the pollution status contributes to these aspects.

Calculation of PLI Index:

Clarification is needed on how the lowest sample concentration is utilized in the calculation of the PLI index. Is the calculation based on both ice and water samples? A more detailed explanation of the methodology employed in deriving this index would contribute to the clarity of the research.

Quality of Figures:

The overall quality of figures, excluding Figure 2, needs improvement. Figures 3 and 4 appear blurry, while the font size in Figure A1 is too small to read comfortably. Additionally, in Figure 7, the references to abcd are unclear; providing labels or a legend to explain these notations is essential. Furthermore, maintaining uniformity in image scales and adopting a consistent numbering system for figures, such as "Fig. A1," would enhance the overall visual presentation.

Reference Format:

The reference format lacks consistency, as both journal abbreviations and full names are used. To enhance clarity and conformity, it is recommended to standardize the format by consistently using either the full names or abbreviations for all journal references.

Author Response

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Author Response File: Author Response.pdf

Reviewer 5 Report

Comments and Suggestions for Authors

Dear Authors

Thanks for your manuscript and results obtained during your campaigns. You achieve an impressive works and try to valorize your data to the best of your ability.

Unfortunately, from my modest point of view, your study suffers from serious shortcomings and unsubstantiated hypotheses. First of all, you use an index without discussing it, even though it concerns trace metals. If you intend to consider this remark, please take into account the limits and biases induced by this index.
Secondly, the quality of your figures is not a credit to your work. Please provide the editor with quality figures, i.e. legible and not blurred, and whose text is sometimes illegible.
Thirdly, the section on altering MPLs needs to be revised. I have put my comments directly into the exte
Finally, be critical and reasonable in your results. What is the point of providing figures after the decimal point? Frankly, who can tell the difference between 324.36 and 324 particles/L? What's more, to your credit and as proof of your seriousness, you provide the standard error. For example, in the abstract of your manuscript: "324.36±261.45 item/L, so what sense does that make? Thank you for remaining consistent and proving that you have some perspective with a calculation that may be precise but must make sense!
The summary needs to be revised and I'm sorry, but because of these serious shortcomings I didn't get as far as reading your conclusions.
I think you'll understand why I'm rejecting your article, but I'd like to invite you, with some serious modifications, to present it again in our journal.
With all due respect for your work, Sustainibility journal and I would like to thank you for your trust and invite you to continue working with the journal.
Respectfully yours

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 6 Report

Comments and Suggestions for Authors

The paper reviewed is based on the spatial distribution of microplastics in one of the cold regions of China.  The research problem is significant as microplastics present a variety of ecological, environmental and ecological risks to natural ecosystems, and this ultimately threatens the ecological integrity of affected catchments.  The research methods for data collection, processing, analyses and interpretation are well accounted for and the same applies to the results and conclusions generated. However, there are few technical and punctual problems to be rectified. The list of corrections is  summarised below. 

List of Corrections:

(1) Under section and subsection, 3. Results. 3.1. Abundance of MPs in ice and water of mainstream Songhua River, you are not allowed to start the subsection by presenting the graphical illustrations first. At least every section or subsection should have about 2-3 lines before the figures or tables are presented. I hope the comment is clearly understood. 

(2) In Line 201-202, the following sentence should be preceded by a full stop and not a comma as currently punctuated: The abundance of MPs increased along Majiagou, and the amount of MPs in urban sampling points(MJ5-MJ9) was much higher than that in suburban and agricultural areas.

(3) Figure 3 shows very important results but their readability and resolution is extremely coarse and it is difficult to read. Please improve the resolution. The same problem applies to Figure 4. 

I hope the comments are carried out effectively  and contribute to the improvement of the paper. 

Comments on the Quality of English Language

The paper reviewed is based on the spatial distribution of microplastics in one of the cold regions of China.  The research problem is significant as microplastics present a variety of ecological, environmental and ecological risks to natural ecosystems, and this ultimately threatens the ecological integrity of affected catchments.  The research methods for data collection, processing, analyses and interpretation are well accounted for and the same applies to the results and conclusions generated. However, there are few technical and punctual problems to be rectified. The list of corrections is  summarised below. 

List of Corrections:

(1) Under section and subsection, 3. Results. 3.1. Abundance of MPs in ice and water of mainstream Songhua River, you are not allowed to start the subsection by presenting the graphical illustrations first. At least every section or subsection should have about 2-3 lines before the figures or tables are presented. I hope the comment is clearly understood. 

(2) In Line 201-202, the following sentence should be preceded by a full stop and not a comma as currently punctuated: The abundance of MPs increased along Majiagou, and the amount of MPs in urban sampling points(MJ5-MJ9) was much higher than that in suburban and agricultural areas.

(3) Figure 3 shows very important results but their readability and resolution is extremely coarse and it is difficult to read. Please improve the resolution. The same problem applies to Figure 4. 

I hope the comments are carried out effectively  and contribute to the improvement of the paper. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 5 Report

Comments and Suggestions for Authors

Dear authors
Thank you for your confidence in MDPI and for choosing our journal. Your work is comprehensive and impressive, and represents a considerable human and financial investment. From a scientific point of view, this work contributes to a better understanding of the risks and challenges for health and the environment of the massive and continuous discharge of plastics into continental waters. I welcome the fact that you mention the risk induced not by the plastics themselves but by the many additives added (organic and inorganic compounds). I also congratulate you by taking into account the capacity of microplastics to transport contaminants.
On the other hand, I don't understand why you continue to provide concentration values with such precision that disservice your work. Can you explain the difference between 2 particles/L and 2.1 or 1.85 particles/L? This is also the same for all of your calculations and statistics! Please keep critical attitude with values obtained by any mathematical and statistical formula. So this point still needs to be revised, if I may say so? Then you use an index (PLI) which, in my opinion, remains to be validated for microplastics, as mentioned in my initial analysis of your manuscript. The last tricky point is the SEM results (Fig.7). As ISO expert, you cannot deduce that the fragments or objects pointed out are plastics or that the defects (cracks, crazing, etc.) are induced by thermic variations. To allow this may I ask you to compare Micorplastic (MPls) before and after ageing by weathering conditions close to natural one observed in the region of the study?
My modest recommandation for you is the following. May I invite you to accept these remarks and suggestions to revise your manuscript to promote it as a valuale one completing thez highst scientific standard? So, and you can contexte my recommandation "major revision". In fcat if you take a little bit more time you ll overpass fastly these defaults!?

Best regards

 

Author Response

Response to Reviewers

Comments from Reviewers:

Thank you for your valuable advice and assistance. Following several days of thorough discussion and careful consideration, our research group would like to provide the following response to your sincere suggestion.

 

[Reviewer #5]Suggestion:

1. On the other hand, I don't understand why you continue to provide concentration values with such precision that disservice your work. Can you explain the difference between 2 particles/L and 2.1 or 1.85 particles/L? This is also the same for all of your calculations and statistics! Please keep critical attitude with values obtained by any mathematical and statistical formula. So this point still needs to be revised, if I may say so?

Thank you for your continuous guidance and valuable comments on our manuscript. We have carefully considered your suggestion regarding the expression of microplastic abundance values and wish to provide further clarification regarding our methodological approach. We concur with your initial recommendation to present abundance values as integers. However, we previously (Round 1) adjusted the values to a single decimal place for greater precision, accompanied by appropriate adjustments in the graphical representations within our article.  Upon reflection, however, we find it essential to articulate the reasoning behind our data presentation decisions, which we hope you may find compelling. Fundamentally, the process of field collecting and transporting ice samples inevitably leads to fragmentation and loss, which invariably introduces minor variances in the volume of the resultant liquid-leading to measurements that are not whole numbers, but rather values such as 9.6 L or 10.03 L, rather than a neat 10 L. This finer degree of measurement allows us to account for the exact amount of microplastics per liter, ensuring that our values reflect the rigorous attention to detail that such scientific study necessitates.  For instance, a sample volume containing 120 microplastics distributed within 10 L of water would yield an average of 12 microplastics per liter – a discrepancy that highlights the importance of maintaining decimal precision in our reported data. It our 2.1 or 1.85 particles/L just represented the mean value of the abundance.

In support of our reasoning, we have also referenced several studies [1-5] (we attached all the references in the attachment in this revision.) that validate the retention of decimal points in reporting data points such as these, indicating that our approach is consistent with established practices in the field. We hope that upon review of our rationale and the supporting literature, you will find our methodological choices justified.  Your acceptance of this aspect of our work would be greatly appreciated, as it reflects a commitment to accuracy and thoroughness. We are thankful for the opportunity to discuss this matter in further detail, and we look forward to your understanding and final decision.

2. Then you use an index (PLI) which, in my opinion, remains to be validated for microplastics, as mentioned in my initial analysis of your manuscript.

Thank you for reaching out with your inquiry. We appreciate the opportunity to address your concerns and explain our methodology. Based on the existing limited means for ecological risk assessment of microplastics, the PLI index has indeed established itself as a robust and extensively adopted metric for gauging environmental pollution, including microplastics. Its utilization extends beyond the realm of heavy metals, having gained recognition for its applicability in assessing microplastic contamination within diverse aquatic, soil, and sediment ecosystems. With the advancement of scientific knowledge and technological tools, the relevance and utility of this index have been reinforced, reflecting the dynamic nature of environmental studies. In light of this, we confidently employed the index in our research, corroborated by its successful application in similar contexts as documented in references [6-8]. We trust that our use of the Tomlinson Pollution Load Index is appropriate for the scope of our study and hope this elucidates the rationale behind our choice.  Your understanding and further guidance are greatly valued as we continue to contribute to the body of knowledge in this important field.

 

3. As ISO expert, you cannot deduce that the fragments or objects pointed out are plastics or that the defects (cracks, crazing, etc.) are induced by thermic variations. To allow this may I ask you to compare Micorplastic (MPls) before and after ageing by weathering conditions close to natural one observed in the region of the study?

We are most grateful for the attention to detail you have brought to your review of our article.  In this study, we have endeavored to examine the surface fragmentation of microplastics through the acute observations provided by electron microscopy, investigating various dimensions and colors of identical polymer types under comparable conditions.It's important to note that our research is grounded in environmental sampling, which, by its nature, offers a unique set of samples distinct from those typically encountered in controlled laboratory settings.  While we recognize the inherent value in comparing our environmental samples with the original materials as obtained commercially, the practicality of such a comparison faces significant challenges.  Given the array of applications and the ensuing difficulty in pinpointing the precise manufacturers of the environmental samples, the potential for a direct comparison regrettably approaches implausibility.

Despite these constraints, we believe that careful observation and the utilization of reference data allow us to hypothesize about the presence of certain structural changes in the microplastics, such as cracks and increased surface roughness.  These features potentially allude to chemical alterations like polymer aging and oxidation, alongside physical transformations which might include mechanical forces and temperature fluctuations, manifesting as grooves on the surface of the microplastics. While it is one of several plausible explanations, we do not claim it to be the definitive cause.  This is substantiated by references [8-10], which inform our understanding of the phenomena at play.

Your further insights and feedback on these considerations would be immensely valuable to us, and we await your learned perspective with high anticipation.

References

1. Chen, J.; Deng, Y.E.; Chen, Y.; Peng, X.; Qin, H.; Wang, T.; Zhao, C.C. Distribution Patterns of Microplastics Pollution in Urban Fresh Waters: A Case Study of Rivers in Chengdu, China. International Journal of Environmental Research and Public Health 2022, 19, doi:10.3390/ijerph19158972.
2. Xia, F.; Liu, H.; Zhang, J.; Wang, D. Migration characteristics of microplastics based on source-sink investigation in a typical urban wetland. Water Res 2022, 213, 118154, doi:10.1016/j.watres.2022.118154.
3. Grbic, J.; Helm, P.; Athey, S.; Rochman, C.M. Microplastics entering northwestern Lake Ontario are diverse and linked to urban sources. Water Research 2020, 174, doi:10.1016/j.watres.2020.115623.
4. Bikker, J.; Lawson, J.; Wilson, S.; Rochman, C.M. Microplastics and other anthropogenic particles in the surface waters of the Chesapeake Bay. Marine Pollution Bulletin 2020, 156, doi:10.1016/j.marpolbul.2020.111257.
5. Jin, X.; Fu, X.D.; Lu, W.J.; Wang, H.T. Fugitive release and influencing factors of microplastics in urbanized watersheds: A case study of the central area of Suzhou City. Science of the Total Environment 2022, 837, doi:10.1016/j.scitotenv.2022.155653.
6. Yin, K.; Wang, D.; Zhao, H.; Wang, Y.; Guo, M.; Liu, Y.; Li, B.; Xing, M. Microplastics pollution and risk assessment in water bodies of two nature reserves in Jilin Province: Correlation analysis with the degree of human activity. Science of The Total Environment 2021, 799, 149390, doi:10.1016/j.scitotenv.2021.149390.
7. Qiu, Y.; Zhou, S.; Zhang, C.; Qin, W.; Lv, C. A framework for systematic microplastic ecological risk assessment at a national scale. Environ Pollut 2023, 327, 121631, doi:10.1016/j.envpol.2023.121631.
8. Prarat, P.; Hongsawat, P. Microplastic pollution in surface seawater and beach sand from the shore of Rayong province, Thailand: Distribution, characterization, and ecological risk assessment. Marine Pollution Bulletin 2022, 174, 113200, doi:10.1016/j.marpolbul.2021.113200.
9. Yan, M.T.; Nie, H.Y.; Xu, K.H.; He, Y.H.; Hu, Y.T.; Huang, Y.M.; Wang, J. Microplastic abundance, distribution and composition in the Pearl River along Guangzhou city and Pearl River estuary, China. Chemosphere 2019, 217, 879-886, doi:10.1016/j.chemosphere.2018.11.093.
10. Wei, H.; Wang, J.; Pan, S.; Liu, J.; Ding, H.; Smith, K.; Yang, Z.; Liu, P.; Guo, X.; Gao, S. Are wastewater treatment plants as the source of microplastics in surface water and soil? J Hazard Mater 2023, 459, 132154, doi:10.1016/j.jhazmat.2023.132154.

 

Author Response File: Author Response.pdf

Round 3

Reviewer 5 Report

Comments and Suggestions for Authors

What sense does it make to mention microparticle concentrations with figures after the comma when you show the variability of the measurements in Figure 2? From my point of view, you're doing yourself a disservice and reducing your work to the level of a Master's report! Next, the hypothesis you put forward about the metals associated with Mpls is not supported, or at least the error of interpretation is obvious. I would remind you that plastics contain fillers such as calcium, silica and, of course, metals. The latter are used, among other things, to colour plastics, so attributing the presence of metals to any mechanism for the adsorption of diluted metals by plastics cannot be deduced from your measurements. If I were you, I would avoid persisting with this scientifically unsupported deduction, which is the result of a blatant bias. Please revisit the discussion (lines 475 & 476).

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