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Article
Peer-Review Record

Distribution Pattern of Dioxins in Sediment Cores from the Xiangxi River, a Tributary of Three Gorges Reservoir, China

Water 2023, 15(1), 57; https://doi.org/10.3390/w15010057
by Bei Zhou 1,2, Kongxian Zhu 2,3, Yonghong Bi 2,*, Bernhard Henkelmann 4, Silke Bernhöft 4, Wujuan Mi 2,* and Karl-Werner Schramm 4,5
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Reviewer 3:
Water 2023, 15(1), 57; https://doi.org/10.3390/w15010057
Submission received: 16 November 2022 / Revised: 16 December 2022 / Accepted: 20 December 2022 / Published: 24 December 2022
(This article belongs to the Special Issue Water Pollution and Its Impact on Human Health)

Round 1

Reviewer 1 Report

The article “Distribution pattern of dioxins in sediment cores from the Xiangxi River, a tributary of Three Gorges Reservoir, China” is devoted to the investigation of the sedimentation, levels and pollution status of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in the sediments of the lower reaches of the Xiangxi River. Certainly, the results of this study can provide some useful information for regional environmental management. However, some parts of the manuscript should be improved. In particular, the Introduction should be enriched and the Results and Discussion should be partially re-written. For these reasons, my decision is major revision.

General comments

Keywords. To maximize discoverability of the manuscript, please avoid repeating words from the title.

Introduction should be extended. Authors should clearly state the scientific issues and novelty of this study. What is remarkable about the Xiangxi River as an object of geochemical research? Have similar studies been carried out in this area before and what did they show? What knowledge gaps are being filled in this study? It is also necessary to provide information on possible sources of PCBs in the study area.

In the Materials and Methods section, references to the used techniques in the description of PCDD/F and carbon analysis are missing. The assessment of PCDD/F toxic equivalents should be described in more detail. Refine the details of the statistical treatment. What software was used for ANOVA and t-test? Which of the ANOVA methods was used? Which of the post hoc criteria were used for multiple comparisons? Has the original data been transformed? Is the PCA based on correlations or covariances? What criterion was used to determine the number of principal components?

Results and discussion:

Check the results of the sediment dating (L. 102–104). It follows from your findings that the deeper the sample, the "younger" it is.

The discussion of the PCDD/F levels should be detailed. The authors use ANOVA to identify differences in the contents of PCDD/F, but do not provide tables of the results of the univariate analysis of variance for each dependent variable, including the sum of squares, mean square between groups, F, and p-value, which allow us to conclude that the differences between the groups are significant. Also, the results of principal component analysis should be presented properly (number of factors, eigenvalues, explained variance, etc.).

Please rewrite and summarize the conclusion section.

The reference list should be extended. Much of the references used are out of date. The potential citation of the article can be significantly improved by adding or replacing some references to modern articles published over the past 5-10 years, as well as current techniques and methods. Thus, the list of references needs to be substantially improved.

Specific comments

L. 15–17. Please split into two separate sentences.

L. 19. Hereinafter, abbreviations should be defined at first mention.

L. 34–36. Reference is required.

L. 55. Please check the style “(WHO 2005, Humans)”. It should be listed in the reference list.

L. 66–68. Reference is required.

L. 75–79. Reference is required.

L. 85–86. Reference is required.

L. 86. EN 13137:2001 should be listed in the reference list.

L. 107–109. Check the style.

L. 119. Reference is required.

L. 121–123. Reference is required.

L. 132–134. Repetition of L. 126–127.

L. 170. Reference is required.

Figure 1. Please add a geographic base to the map.

Figure 2. Please add different letters to indicate significant differences between groups resulting from post hoc tests.

Table 2. All abbreviations should be explained in footnotes of the table.

Please, pay attention to typos in the text:

L. 20. Add space “p<0.05”.

L. 23. Add space “p>0.05”.

L. 92. Add space “90cm”.

L. 112. Extra period “rivers. (pg/g”.

L. 129. “On the other hand, The vertical distribution”.

Author Response

Response to Reviewer 1 Comments

General comments: The article “Distribution pattern of dioxins in sediment cores from the Xiangxi River, a tributary of Three Gorges Reservoir, China” is devoted to the investigation of the sedimentation, levels and pollution status of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in the sediments of the lower reaches of the Xiangxi River. Certainly, the results of this study can provide some useful information for regional environmental management. However, some parts of the manuscript should be improved. In particular, the Introduction should be enriched and the Results and Discussion should be partially re-written. For these reasons, my decision is major revision.

Response: Thank you very much for your positive comments. We agree with you that this manuscript provided some useful information for regional environmental management. In the revision, we enriched the introduction section, the results and discussion were rewritten, some valuable information was added.

 

Point 1:Keywords. To maximize discoverability of the manuscript, please avoid repeating words from the title.

Response: Thank you for your advice, we changed the keywords.

 

Point 2:Introduction should be extended. Authors should clearly state the scientific issues and novelty of this study. What is remarkable about the Xiangxi River as an object of geochemical research? Have similar studies been carried out in this area before and what did they show? What knowledge gaps are being filled in this study? It is also necessary to provide information on possible sources of PCBs in the study area.

Response: We extended the introduction and clearly state the scientific issues. Due to tributary environmental risk is important to the TGR, the largest reservoir in the world. It is necessary to investigate the persistent organic pollutant. Data in this manuscript would provide information of POPS, which helped us to get insight into the environmental risk of POPS. Xiangxi river is the longest river of TGR in the Hubei province, many ecological and environmental problems occurred after the impoundment of TGR. This river was paid attention to by the experts. No similar studies have been conducted in this area. This manuscript provided data on dioxins distribution in this river and TEQ was assessed. All results gave information on dioxins in this river. Though the concentrations of dioxins and its TEQ were low, this manuscript gave evidence that dioxins could be ignored when environmental risk was evaluated.

 

 

Point 3:In the Materials and Methods section, references to the used techniques in the description of PCDD/F and carbon analysis are missing. The assessment of PCDD/F toxic equivalents should be described in more detail. Refine the details of the statistical treatment. What software was used for ANOVA and t-test? Which of the ANOVA methods was used? Which of the post hoc criteria were used for multiple comparisons? Has the original data been transformed? Is the PCA based on correlations or covariances? What criterion was used to determine the number of principal components?

Response: We revised the materials and methods section. Some references were added.  Including the reference on the assessment of PCDD/F toxic equivalents. The statistical treatment was refined. The sample stations were clustered based on the dioxins composition and their content in each sample.

 

Point 4: Results and discussion:

Check the results of the sediment dating (L. 102–104). It follows from your findings that the deeper the sample, the "younger" it is.

Response: Sorry for this mistake. Each core was sliced into 10 cm fractions (samples) with a spatula from the bottom to the top layers; so, the deeper the sample, the older it was. We have modified this information in the materials and methods.

 

Point 5:The discussion of the PCDD/F levels should be detailed. The authors use ANOVA to identify differences in the contents of PCDD/F, but do not provide tables of the results of the univariate analysis of variance for each dependent variable, including the sum of squares, mean square between groups, F, and p-value, which allow us to conclude that the differences between the groups are significant. Also, the results of principal component analysis should be presented properly (number of factors, eigenvalues, explained variance, etc.).

Response: PCDD/F concentrations in the three sediment cores were the data for one-way ANOVA. n=18 was added in the manuscript. Some data was provided in table 2 and figure 2. As to the PCA analysis, we used the dioxins data to cluster the sample stations, not for the explained variance identified.

 

Point 6: The reference list should be extended. Much of the references used are out of date. The potential citation of the article can be significantly improved by adding or replacing some references to modern articles published over the past 5-10 years, as well as current techniques and methods. Thus, the list of references needs to be substantially improved.

Response: References were changed in the revision.

 

Point 7: Specific comments

  1. 15–17. Please split into two separate sentences.
  2. 19. Hereinafter, abbreviations should be defined at first mention.
  3. 34–36. Reference is required.
  4. 55. Please check the style “(WHO 2005, Humans)”. It should be listed in the reference list.
  5. 66–68. Reference is required.
  6. 75–79. Reference is required.
  7. 85–86. Reference is required.
  8. 86. EN 13137:2001 should be listed in the reference list.
  9. 107–109. Check the style.
  10. 119. Reference is required.
  11. 121–123. Reference is required.
  12. 132–134. Repetition of L. 126–127.
  13. 170. Reference is required.

Figure 1. Please add a geographic base to the map.

Response:  All these questions have been revised point-to-point.

 

 

Point 8: Figure 2. Please add different letters to indicate significant differences between groups resulting from post hoc tests.

Response: Figure 2 was changed according to your advice.

 

Point 9: Table 2. All abbreviations should be explained in footnotes of the table.

Please, pay attention to typos in the text:

  1. 20. Add space “p<0.05”.
  2. 23. Add space “p>0.05”.
  3. 92. Add space “90cm”.
  4. 112. Extra period “rivers. (pg/g”.
  5. 129. “On the other hand, The vertical distribution”.

Response: All these questions have been revised point-to-point.

Reviewer 2 Report

Line 77    .....was....

104 Should the sequence of dates be reversed? The shallowest sample should be the most modern.

Table 1. Pb-210 has high concentrations in A7 and A8.

Table 3. Germany

Reference No. 2   ( ) What is this?

Author Response

Response to Reviewer 2 Comments

Point 1: Line 77    .....was....

Response: It was revised.

 

Point 2:104 Should the sequence of dates be reversed? The shallowest sample should be the most modern.

Response: Sorry for this mistake, Each core was sliced into 10 cm fractions (samples) with a spatula from the bottom to the top layers; so, the deeper the sample, the older it was. We have modified this information in the materials and methods.

 

Point 3:Table 1. Pb-210 has high concentrations in A7 and A8.

Response: Thank you for your comments. The data was a mistake in writing. We have modified it.

 

Point 4:Reference No. 2   ( ) What is this?

Response: ( ) was deleted in the revision.

Reviewer 3 Report

Dear authors,

Your paper needs to be improved. Below, I point to its numerous problems. When you correct them, it would be quite a different paper. Please do think if your data are enough for a journal article. 

Abstract: No significant difference was found in TEQ (p>0.05). I don’t understand what it is and where it is from.

Radiometric dates data not properly presented

OCDD, TEQ in abstract need defining/abbreviations listed?

Figure 1. Sketch map of the Xiangxi River and the sample station – Maybe stations?

Line 77 wase?

Lines 99-104 not easy to understand. Clear and undis-101 turbed 210Pb gradients in different layers indicated that the data were credible. The sedi-102 ment accumulation rates calculated by 210Pb were 1.01 cm/a, and that the dates of samples 103 A3, A4, A5 and A6 were from the 1960s, 1970s, 1980s and 1990s, respectively. -- Where did all these data come from? Please give the data accurately with error bars. Please explain to me why samples with less depth are older.

 relative regular change – please write what this is based on.

Table 2 ΣPCDD/Fs / TOC* Does it have an experimental error? What is n.d.? Below detection limit or not done?

The mean PCDD/F concentrations in the sediment core from upstream, midstream 113 and downstream were 24.40 pg/g d.w., 20.12 pg/g d.w. and 46.91 pg/g d.w., respectively. --  Exp errors please!

OCDD and OCDF What are these?

Line 12 defended better treated?

Define all abbreviations

Please error bars in Fig 2

Why not distinction of upstream from midstream samples? Either of these kinds of samples  group on the PCA plot.

Where did you use ref 16?

What () in ref list mean?

You gave no evidence that dioxins come from Na-PCP, but you claim they come from Na-PCP? Did you find Na-PCP in your samples?

Many English words are wrongly used. Let an English speaker correct your paper.

Author Response

Response to Reviewer 3 Comments

Point 1:Your paper needs to be improved. Below, I point to its numerous problems. When you correct them, it would be quite a different paper. Please do think if your data are enough for a journal article. 

Response: Thank you very much for your evaluation.

 

Point 2:Abstract: No significant difference was found in TEQ (p>0.05). I don’t understand what it is and where it is from.

Response: Though no significant difference was found in TEQ, data on dioxins in this area was valuable. Without data, we don’t know what it is. So, data in this manuscript was important base data.

 

Point 3:Radiometric dates data not properly presented

Response: Sorry for this mistake, we have modified this according to the original data.

 

Point 4:OCDD, TEQ in abstract need defining/abbreviations listed?

Response: We have modified it according to your advice.

 

Point 5:Figure 1. Sketch map of the Xiangxi River and the sample station – Maybe stations?

Response: This information was modified.

 

Point 6:Line 77 wase?

Response: It was a mistake, “wase” is “was”, we modified this.

 

Point 7:Lines 99-104 not easy to understand. Clear and undis-101 turbed 210Pb gradients in different layers indicated that the data were credible. The sediment accumulation rates calculated by 210Pb were 1.01 cm/a, and that the dates of samples 103 A3, A4, A5 and A6 were from the 1960s, 1970s, 1980s and 1990s, respectively. -- Where did all these data come from? Please give the data accurately with error bars. Please explain to me why samples with less depth are older.

Response: We have added the sediment rate measurement in the materials and methods. Data on the 210Pb was checked according to the original data.

 

Point 8:Table 2 ΣPCDD/Fs / TOC* Does it have an experimental error? What is n.d.? Below detection limit or not done?

Response: ΣPCDD/Fs / TOC* meant the significant relationship between ΣPCDD/Fs and TOC; n.d. was Not detectable.

 

Point 9:The mean PCDD/F concentrations in the sediment core from upstream, midstream and downstream were 24.40 pg/g d.w., 20.12 pg/g d.w. and 46.91 pg/g d.w., respectively. --  Exp errors please!

Response: Data was modified according to your advice.

Point 10:OCDD and OCDF What are these?

Response: All abbreviations were defined in table 2.

 

Point 11:Line 12 defended better treated?

Response: It was modified.

 

Point 12:Define all abbreviations

Response: All abbreviations were defined in table 2.

 

Point 13:Please error bars in Fig 2

Response: Error bars were added in Fig.2.

 

Point 14:Why not distinction of upstream from midstream samples? Either of these kinds of samples group on the PCA plot.

Response: Based on PCA analysis, the sample stations were clustered in two groups. No significant difference could be found between the upstream and the midstream.

 

Point 15:Where did you use ref 16?

Response: This reference was deleted.

 

Point 16:What () in ref list mean?

Response:  () was deleted from the manuscript.

 

Point 17:You gave no evidence that dioxins come from Na-PCP, but you claim they come from Na-PCP? Did you find Na-PCP in your samples?

Response: We agree with you. The conclusion was modified as “by-products of sodium pentachlorophenate might be the main source.”

 

Point 18:Many English words are wrongly used. Let an English speaker correct your paper.

Response: We corrected the manuscript.

Round 2

Reviewer 1 Report

 

Dear authors,

As a result of the revision, all the necessary changes were made to the structure of the article, the description of the experimental part was supplemented, and the presentation of the results was strengthened. I recommend the article for publication.

Best regards.

 

Reviewer 3 Report

Dear authors, please remove "12 defended better treated" from Line 173 and replace "defended" in Line 181 with"treated".  Otherwise I think your paper is OK

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