Insights on the Abiotic/Biotic Interactive Impacts on the Occurrence of PFASs in Municipal Solid Waste Landfill Leachate
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript investigates the occurrence and environmental behavior of per- and polyfluoroalkyl substances (PFAS) in landfill leachate, considering abiotic and biotic factors. It offers significant insights into the interaction of dissolved organic matter (DOM) and microbial diversity with PFAS transportation and transformation. This study is highly relevant to the field of environmental science and provides valuable data for PFAS risk management.
Strengths
- Relevance: The manuscript addresses a critical environmental issue—PFAS contamination in landfill leachate, with a focus on an underexplored region.
- Methodological Rigor: A comprehensive analysis of PFAS concentrations, DOM composition, and microbial diversity is performed.
- Data Presentation: Detailed statistical analysis, including spectroscopic and molecular data, enhances the study's credibility.
Weaknesses
- Similarity Index: The manuscript shows a high similarity (9%) with a published article (Li et al., 2024). The similarity percentage should be reduced to less than 3%.
- Introduction and Methods: Redundant phrases and lack of clarity in some sections need improvement.
- Inconsistent Reporting: There are discrepancies in reported PFAS numbers (17 vs. 22) in the methods section.
- Language Issues: Some sentences lack precision or are unnecessarily lengthy.
Comments and Suggestions
- Introduction:
- L49: Define PFOS and PFOA fully upon first mention.
- L52-54: Edit to "Landfill sites known to receive industrial waste containing PFOS and PFOA have recorded PFOS concentrations up to 82,000 ng/L and PFOA concentrations up to 31,054 ng/L in municipal solid waste (MSW) leachate."
- L57-59: Rephrase as "As shown in existing studies [11], the DOM in the leachate will adsorb PFAS, promoting their release from the landfill and further transport to the environment with the leachate."
- L60: Change ‘Dissolved organic matter (DOM)’ to ‘DOM.’
- L81: Edit to "with different landfill ages and specifications."
- Materials and Methods:
- L98-112: Avoid repeating "solid phase extraction column" multiple times; use "the column" instead.
- L109-112: Edit to "The collected eluent was concentrated to near-dryness under high-purity nitrogen using a nitrogen evaporator, reconstituted with 1 mL of initial mobile phase, filtered through a 0.22 μm membrane, and stored in a 1.5 mL amber vial at 4 °C until LC-MS/MS analysis."
- Reference for sample pretreatment method is missing.
- L116-117: Edit to "The mobile phase consisted of 5 mM ammonium acetate (A) and methanol (B), delivered at a flow rate of 0.4 mL/min."
- L138-143: Clarify whether 17 or 22 PFAS were analyzed. This inconsistency needs correction.
- Results and Discussion:
- L421-422: Edit to "The relative abundance of Campylobacterota in all samples ranged from 0.01% to 51.93%, and the average abundance was 14.03%."
- L428-433: Simplify the sentence structure; it is too long.
- L451-454: Edit to "It is worth noting that sodium, chromium, and chloride ion concentrations significantly affected the levels of various PFAS. Previous studies have shown the influence of ionic strength on PFAS adsorption varies across different media."
- L549-550: Edit to "PFAS was found in all leachate samples, with concentrations ranging from 1328 to 37447 ng/L."
- Conclusion:
- L545: Change "Conclusions" to "Conclusion."
- L546: Replace "paper" with "research."
Recommendation
Minor revision is recommended to address the highlighted issues and comments.
Comments on the Quality of English LanguageThe English language quality was generally good, though minor revisions suggested in the review reports (for authors) should be addressed.
Author Response
R1：
Comments and Suggestions for Authors
The manuscript investigates the occurrence and environmental behavior of per- and polyfluoroalkyl substances (PFAS) in landfill leachate, considering abiotic and biotic factors. It offers significant insights into the interaction of dissolved organic matter (DOM) and microbial diversity with PFAS transportation and transformation. This study is highly relevant to the field of environmental science and provides valuable data for PFAS risk management.
Response: Thanks for your positive comments!
Strengths
1.Relevance: The manuscript addresses a critical environmental issue—PFAS contamination in landfill leachate, with a focus on an underexplored region.
Response: Thanks for your positive comments!
2.Methodological Rigor: A comprehensive analysis of PFAS concentrations, DOM composition, and microbial diversity is performed.
Response: Thanks for your positive comments!
3.Data Presentation: Detailed statistical analysis, including spectroscopic and molecular data, enhances the study's credibility.
Response: Thanks for your positive comments!
Weaknesses
1.Similarity Index: The manuscript shows a high similarity (9%) with a published article (Li et al., 2024). The similarity percentage should be reduced to less than 3%.
Response: Thank you for your comments. The published article (Li et al., 2024) was written by us too. And we have revised the manuscript and the similarity percentage has been reduced to less than 3%.
2.Introduction and Methods: Redundant phrases and lack of clarity in some sections need improvement.
Response: Thank you for your comments. We have polished the sentences in Introduction and Methods part to avoid the redundant phrases and lack of clarity. Please kindly see Section 2.2 and 2.5.
3.Inconsistent Reporting: There are discrepancies in reported PFAS numbers (17 vs. 22) in the methods section.
Response: Thank you for your comments. We have clarified that 22 PFAS were analyzed in Line 131.
4.Language Issues: Some sentences lack precision or are unnecessarily lengthy.
Response: Thank you for your comments. We have asked a native English speaker to facilitate polishing the English and the sentences are now in precision and not lengthy.
Comments and Suggestions
Introduction:
L49: Define PFOS and PFOA fully upon first mention.
Response: Thanks for your comments. We have added the full definition of PFOS and PFOA in Line 48.
L52-54: Edit to "Landfill sites known to receive industrial waste containing PFOS and PFOA have recorded PFOS concentrations up to 82,000 ng/L and PFOA concentrations up to 31,054 ng/L in municipal solid waste (MSW) leachate."
Response: Thanks for your comments. We have edited the sentence in Lines 52-55.
L57-59: Rephrase as "As shown in existing studies [11], the DOM in the leachate will adsorb PFAS, promoting their release from the landfill and further transport to the environment with the leachate."
Response: Thanks for your comments. The expression has been rephrased as your comment in Lines 56-58.
L60: Change ‘Dissolved organic matter (DOM)’ to ‘DOM.’
Response: Thanks for your comments. ‘Dissolved organic matter (DOM)’ has been changed to ‘DOM’ in Line 58.
L81: Edit to "with different landfill ages and specifications."
Response: Thanks for your comments. We have edited the sentence in Line 79.
Materials and Methods:
L98-112: Avoid repeating "solid phase extraction column" multiple times; use "the column" instead.
Response: Thanks for your comments. We have used "the column" instead of "solid phase extraction column" in Lines 102-103.
L109-112: Edit to "The collected eluent was concentrated to near-dryness under high-purity nitrogen using a nitrogen evaporator, reconstituted with 1 mL of initial mobile phase, filtered through a 0.22 μm membrane, and stored in a 1.5 mL amber vial at 4 °C until LC-MS/MS analysis."
Reference for sample pretreatment method is missing.
Response: Thanks for your comments. We have edited the sentence and added the reference in Lines 104-107.
L116-117: Edit to "The mobile phase consisted of 5 mM ammonium acetate (A) and methanol (B), delivered at a flow rate of 0.4 mL/min."
Response: Thanks for your comments. We have edited the sentence in Lines 110-111.
L138-143: Clarify whether 17 or 22 PFAS were analyzed. This inconsistency needs correction.
Response: Thanks for your comments. We have clarified that 22 PFAS were analyzed in Line 131.
Results and Discussion:
L421-422: Edit to "The relative abundance of Campylobacterota in all samples ranged from 0.01% to 51.93%, and the average abundance was 14.03%."
Response: Thanks for your comments. We have edited the sentence in Lines 410-411.
L428-433: Simplify the sentence structure; it is too long.
Response: Thanks for your comments. The sentence has been simplified in Lines 417-420.
L451-454: Edit to "It is worth noting that sodium, chromium, and chloride ion concentrations significantly affected the levels of various PFAS. Previous studies have shown the influence of ionic strength on PFAS adsorption varies across different media."
Response: Thanks for your comments. We have edited the sentence in Lines 439-442.
L549-550: Edit to "PFAS was found in all leachate samples, with concentrations ranging from 1328 to 37447 ng/L."
Response: Thanks for your comments. We have edited the sentence in Lines 538-539.
Conclusion:
L545: Change "Conclusions" to "Conclusion."
Response: Thanks for your comments. "Conclusions" has been changed to "Conclusion” in Line 534.
L546: Replace "paper" with "research."
Response: Thanks for your comments. "Paper" has been replaced with "research” in Line 535.
Recommendation
Minor revision is recommended to address the highlighted issues and comments.
Response: Thanks for your positive comments!
Comments on the Quality of English Language
The English language quality was generally good, though minor revisions suggested in the review reports (for authors) should be addressed.
Response: Thanks for your comments. We have asked a native English speaker to facilitate polishing the English in the whole manuscript.
Reviewer 2 Report
Comments and Suggestions for AuthorsA very interesting work indeed, with a huge amount of work in terms of the number of experiments carried out and a good analysis of an interesting topic. However, the article would be even better if it were improved by the following observations:
1. Please identify when and where the samples were taken;
2. Please clarify Figures 1, 3, 4, 6, as it is not clear what is depicted.
3. Which of the sorbents sorbs best to PSAF. Please explain in the text?
4. Could you please provide an SEM image of the sorbent with PSAF if this is possible?
5. I missed the discussion in the presented results. Very much everything is presented as factual material, but maybe more can be explained and compared with studies done by other scientists.
6. Maybe the conclusions could present not only the facts but also future research related to the facts, what more can be done on this issue, and how it can be continued.
7. Please describe what problems have arisen in researching this topic?
8. Is this a follow-up study and what has been done before? Please answer.
9. Statistical estimates are not given everywhere in the text or charts. Please improve.
10. English is not bad but needs some improvement.
If the manuscript is corrected and improved, then this will be a work of really high value and significance.
Author Response
R2：
Comments and Suggestions for Authors
A very interesting work indeed, with a huge amount of work in terms of the number of experiments carried out and a good analysis of an interesting topic. However, the article would be even better if it were improved by the following observations:
Response: Thanks for your positive comments!
- Please identify when and where the samples were taken;
Response: Thanks for your comments. The details about sampling were provided in 2.1. sample collection in Lines 87-88.
- Please clarify Figures 1, 3, 4, 6, as it is not clear what is depicted.
Response: Thanks for your comments.
Figure 1 depicts the concentration and distribution of PFAS in leachate from 16 landfills. PFAS can be classified into three categories according to functional groups: PFAA, PFCA and PFSA (fig. 1a). The concentrations of every kind of PFAS were shown in fig. 1b. Fig. 1c shows the concentrations of different types of PFAS were analyzed. Fig. 1d demonstrate the concentrations of PFAS that classified by carbon chain length.
Figure 3 depicts the proportion of different components (a) and compound composition (b) of dissolved organic matter in 16 landfill samples. The results were obtained from FT-ICR-MS characterization.
Figure 4 depicts the molecular Van Krevelen diagrams of DOM from leachate, which were derived from FT-ICR-MS characterization.
Figure 6 depicts demonstrated the spearman correlation analyses between PFAS and characteristics, DOM components and microbes.
- Which of the sorbents sorbs best to PSAF. Please explain in the text?
Response: Thanks for your comments. Regrettably, our work did not contain the sorption materials for PFAS. Our work focused on the occurrence and transport mechanism of PFAS in landfill leachate.
- Could you please provide an SEM image of the sorbent with PSAF if this is possible?
Response: Thanks for your comments. We are sorry that we did not test any sorbents.
- I missed the discussion in the presented results. Very much everything is presented as factual material, but maybe more can be explained and compared with studies done by other scientists.
Response: Thanks for your comments. We have added some discussion and comparison in section 3.2, section 3.5.1 and section 3.5.2. Please kindly see Lines 265-268, 456-459 and 464-486 and etc.
- Maybe the conclusions could present not only the facts but also future research related to the facts, what more can be done on this issue, and how it can be continued.
Response: Thanks for your comments. We have added that part in conclusion. Please kindly see Lines 561-568.
- Please describe what problems have arisen in researching this topic?
Response: Thanks for your comments. Although the removal rate of PFASs in the existing leachate treatment processes (such as biological treatment, membrane treatment, etc.) can be as high as 99.8%, the problem of precursor contamination and transformation still exists in the treatment process. This means that during the treatment process, the precursor substances of PFAS may be converted into other forms of PFAS, thus affecting the treatment effect. The environmental fate of by-products produced in the treatment process is not fully defined. This means that we have a poor understanding of the behavior and effects of these by-products in the environment, which can pose potential risks to ecosystems. Rainfall, leachate recharge, physical and chemical properties of leachate and other factors can affect the occurrence characteristics of PFASs, but the specific influencing mechanism has not been clarified. This limits our understanding of the behavior of PFAS in landfill leachate and also affects the optimization of treatment techniques.
- Is this a follow-up study and what has been done before? Please answer.
Response: Thanks for your comments. This is a follow-up study. Our previous study was published in Environmental research. The study demonstrated that the frequency of PFAS detection in the samples was 100%, and the PFAS concentrations in leachate were greater than in the groundwater samples. Physicochemical factors, such as ammonium-nitrogen (NH4+-N), sodium (Na), calcium (Ca), DOM components C4 (macromolecular humic acid), SUVA254 (aromatic component content), and A240-400 (humification degree and molecular weight), were strongly correlated with PFAS concentrations.
- Li, H.Q. Sha, W.J. Liu, Y. Yuan, G.H. Zhu, F.H. Meng, B.D. Xi, W.B. Tan, Transport of per-/polyfluoroalkyl substances from leachate to groundwater as affected by dissolved organic matter in landfills, Environ. Res, 247 (2024) 118230.
- Statistical estimates are not given everywhere in the text or charts. Please improve.
Response: Thanks for your comments. We have given the statistical estimates in Fig. 7 in Lines 525-532.
- English is not bad but needs some improvement.
Response: Thanks for your comments. We have asked a native English speaker to facilitate polishing the English in the whole manuscript.
If the manuscript is corrected and improved, then this will be a work of really high value and significance.
Response: Thanks for your positive comments!
Reviewer 3 Report
Comments and Suggestions for AuthorsIn this manuscript, the authors describe the analysis of polyfluoroalkyl substances (PFAS) in landfill leachate as well as physical, chemical and microbial indexes to understand as these PFAS can be affected the environmental behavior of PFAS in landfill leachate. Correlation analysis from these data reveal interesting approaching to understanding the risk management of these PFAS. The research work is very interesting, all results are well-performed.
I suggest the following minor revisions to further improve the interpretations of some results.
Here is my observation:
1.- In section 2.5: Determination of microbial diversity in leachate. Is necessary a major description of these methodology to understand as DNA was obtained from direct samples, because some time landfill leachate can cause inhibition during DNA purification. Also diversity index and genes annotation require a major description. Sequencing data accession number is missing.
2.- In results, section 3.5.2. Effects of biotic factors on the occurrence of PFAS in leachate: The correlation analysis with some microbial taxonomic groups is interesting, but probably PFAS can be only one of diverse toxic substances that can affect abundance of these microbial taxonomic group, so that my recommendation is that these results interpretation can be edited a little bit.
Author Response
R3：
Comments and Suggestions for Authors
In this manuscript, the authors describe the analysis of polyfluoroalkyl substances (PFAS) in landfill leachate as well as physical, chemical and microbial indexes to understand as these PFAS can be affected the environmental behavior of PFAS in landfill leachate. Correlation analysis from these data reveal interesting approaching to understanding the risk management of these PFAS. The research work is very interesting, all results are well-performed.
Response: Thanks for your positive comments!
I suggest the following minor revisions to further improve the interpretations of some results.
Here is my observation:
1.- In section 2.5: Determination of microbial diversity in leachate. Is necessary a major description of these methodology to understand as DNA was obtained from direct samples, because some time landfill leachate can cause inhibition during DNA purification. Also diversity index and genes annotation require a major description. Sequencing data accession number is missing.
Response: Thanks for your comments. The details have been provided in Supplementary Information. Please kindly see Text S1 in Line 192.
2.- In results, section 3.5.2. Effects of biotic factors on the occurrence of PFAS in leachate: The correlation analysis with some microbial taxonomic groups is interesting, but probably PFAS can be only one of diverse toxic substances that can affect abundance of these microbial taxonomic group, so that my recommendation is that these results interpretation can be edited a little bit.
Response: Thanks for your comments. We have edited the results interpretation in section 3.5.2. in Lines 464-486.
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThanks a lot for the corrections.
