Characteristics, Sources, and Risk Assessment of Polycyclic Aromatic Hydrocarbons in Soils and Sediments in the Yellow River Delta, China

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript focuses on the distribution, sources, and ecological and health risk assessment of polycyclic aromatic hydrocarbons (PAHs) in the soils of uncultivated land and coastal beach sediments in China's Yellow River Delta. This topic is highly significant for understanding PAH pollution characteristics and ecological risks in typical wetland ecosystems and is closely related to current environmental research hotspots and practical needs. The study employs a comprehensive methodology, including sample collection, gas chromatography-mass spectrometry analysis, positive matrix factorization (PMF) modeling, and ecological and health risk assessments, to thoroughly investigate PAHs from multiple analytical perspectives, enhancing the credibility of the results. However, there are some minor issues that need addressing before acceptance.

 

1. It would be advisable to appropriately incorporate citations from recent relevant studies when introducing the sources of PAHs and risk assessment methodologies. Consider including references to the latest monitoring techniques (e.g., passive sampling methods) and novel risk evaluation frameworks published within the past five years.
2. The author is recommended to strengthen the discussion by incorporating concrete risk mitigation and pollution management strategies. Such an improvement would considerably enhance the paper's practical applicability and its value in guiding environmental governance. For instance, it could be proposed prioritizing the control of high-risk areas based on spatial distribution patterns, along with other relevant measures.

3. Some of the text and images in the manuscript are not aligned and deviate from the page. It is recommended that the author carefully check and revise them

Author Response

Comment 1: It would be advisable to appropriately incorporate citations from recent relevant studies when introducing the sources of PAHs and risk assessment methodologies. Consider including references to the latest monitoring techniques (e.g., passive sampling methods) and novel risk evaluation frameworks published within the past five years.

Response: We have added three recent studies in the introduction section, covering passive sampling techniques and machine learning algorithms risk assessment models, to enhance the theoretical support and reflect recent progress.

Comment 2: The author is recommended to strengthen the discussion by incorporating concrete risk mitigation and pollution management strategies. Such an improvement would considerably enhance the paper's practical applicability and its value in guiding environmental governance. For instance, it could be proposed prioritizing the control of high-risk areas based on spatial distribution patterns, along with other relevant measures.

Response: We have added a paragraph in the discussion section proposing to prioritize the control of high-risk zones based on spatial distribution patterns, thus enhancing the practical applicability of the study.

Comment 3: Some of the text and images in the manuscript are not aligned and deviate from the page. It is recommended that the author carefully check and revise them.

Response: We have carefully reviewed and standardized the layout of all texts and figures to ensure clarity and alignment.

Reviewer 2 Report

Comments and Suggestions for Authors

1. In general, the manuscript is well structured, interesting and enjoyable, but I would like to recommend that the list of references be updated with some more current ones or, failing that, add to the list of references some that are of great relevance and preferably more current up to the present date.
2. I recommend adding the information legend at the bottom of table 5, just as it does in table 3.
3. I recommend modifying Figure 2, using another type of colors where the spatial distribution of PAHs can be better appreciated. An example could be using a gradient of shades from red to yellow, and that the information legends include at least an intermediate value between the highest and lowest concentration of PAHs, so that the image can be better understood.
4. Translate the title of the “x” axis in Figure 4 b) into English.
5. Avoid the use of “In summary” when writing the conclusions, it is not about summarizing the results but about stating your conclusion as to whether your results met the objectives stated in your introduction.

Author Response

Comment 1: In general, the manuscript is well structured, interesting and enjoyable, but I would like to recommend that the list of references be updated with some more current ones or, failing that, add to the list of references some that are of great relevance and preferably more current up to the present date.

Response: We have updated the reference list by including relevant studies published between 2021 and 2024 to reflect recent developments.

Comment 2: I recommend adding the information legend at the bottom of table 5, just as it does in table 3

Response: A legend has been added below Table 5 to clarify abbreviations and statistical terms.

Comment 3: I recommend modifying Figure 2, using another type of colors where the spatial distribution of PAHs can be better appreciated. An example could be using a gradient of shades from red to yellow, and that the information legends include at least an intermediate value between the highest and lowest concentration of PAHs, so that the image can be better understood.

Response: Thank you for your suggestion. We have modified Figure 2, using a gradient color from yellow to red and setting the median value.

Comment 4: Translate the title of the “x” axis in Figure 4 b) into English.

Response: Thank you for your attention to language clarity. The x-axis title in Figure 4b has been translated from Chinese to English.

Comment 5: Avoid the use of “In summary” when writing the conclusions, it is not about summarizing the results but about stating your conclusion as to whether your results met the objectives stated in your introduction.

Response: We appreciate this stylistic recommendation. The conclusion section has been fully revised to avoid generic phrasing and instead directly state how the study met its stated objectives regarding PAH concentration analysis, source apportionment, and risk evaluation.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is generally well written and presents important data in  view of YRD pollution and its risk to environment and humans. However, in present form it needs major revision according to the comments listed below:

Comment 1: The title is too long and should not be repeated in keywords in total.

Comment 2: Give references as numbers.

Comment 3: Line numbering would facilitate review preparation.

Comment 4: Provide information on PAH health risk due to their metabolism to highly toxic derivatives, even more toxic than parent compound and able to damage DNA. Provide relevant references.

Comment 5: Describe in detail sampling procedure, give information on “stainless steel devises” used.

Comment 6: Add the description of extraction procedure as 2.3. subsection followed by analysis and quality control of results. Provide number of analytical replicates for each sampling site.

Comment 7: Improve the quality of all figures (font size, remove frames, replace axis description in Chinese)

 

Author Response

Comment 1: The title is too long and should not be repeated in keywords in total.

Response: Thank you for your attention to language clarity. We have shortened the title.

Comment 2: Give references as numbers.

Response: The referencing format has been changed to numerical citation style throughout the manuscript.

Comment 3: Line numbering would facilitate review preparation.

Response: Line numbers have been added to the revised manuscript to aid in review.

Comment 4: Provide information on PAH health risk due to their metabolism to highly toxic derivatives, even more toxic than parent compound and able to damage DNA. Provide relevant references.

Response: We have added a brief explanation of the metabolic activation of PAHs and their DNA-damaging potential, along with relevant references, in the health risk assessment section.

Comment 5: Describe in detail sampling procedure, give information on “stainless steel devises” used.

Response: Thank you for the helpful suggestion. In response, we have revised Section 2.2 to clarify the sampling method. We specified that surface soils (0–20 cm) were collected using decontaminated stainless steel shovels and augers. Three replicates were taken at each site, and approximately 1 kg of each homogenized sample was stored in opaque polyethylene Ziplock bags, then transported under cold conditions and frozen at −20 °C until analysis.

Comment 6: Add the description of extraction procedure as 2.3. subsection followed by analysis and quality control of results. Provide number of analytical replicates for each sampling site.

Response: Thank you for your valuable suggestion. In response, we have revised Section 2.3 to explicitly include the extraction procedure. We added details regarding the use of 200 mL of acetone:n-hexane (1:1) for Soxhlet extraction over 16-18 hours, the silica gel column specifications, and the elution process with dichloromethane : pentane. Additionally, we clarified that each sample was analyzed in duplicate to ensure reproducibility.

Comment 7: Improve the quality of all figures (font size, remove frames, replace axis description in Chinese).

Response: All figures have been revised to improve visual clarity and all axis labels have been translated into English.

Reviewer 4 Report

Comments and Suggestions for Authors

Remarks:

 

• Insufficient methodological detail – site selection: Manuscript describes using a grid method to select sampling sites in areas “less affected by human activities”. How large was the grid spacing? What criteria were used to decide a site was “less affected” or “far away” from roads and farmland?

 

• Sample replicate handling unclear: Manuscript states “three replicates at each site” were collected. The manuscript never clarifies what was done with these replicates. Were they combined into one composite sample per site, or analyzed separately (and if so, how were the results averaged or reported)? Also, if replicates were averaged, reporting the within-site variance might be helpful.

 

• Sample preparation not presented: Big problem, not any info about sample preparation prior to GC-MS.

 

• Imbalance in sample numbers (soil vs. sediment): The study uses 32 soil samples but only 6 sediment samples. This large discrepancy is problematic and is not justified in the text. Six sediment samples for a whole delta coastline is a very sparse coverage – it undermines the ability to generalize about sediment PAH pollution. The authors should explicitly acknowledge this limitation and avoid over-interpreting sediment spatial trends.

 

• Inconsistent units and unit notation: The manuscript mixes unit notations in a confusing way. Concentrations are given in ng/g in the text and tables for results, which is appropriate. However, the QA/QC section reports LOD and LOQ in mg/kg. Moreover, Table 2 lists Exposure frequency as “d/a” (days per annum) and exposure duration as “a” (years), which are non-standard abbreviations. It’s better to use “days/year” and “years” or “d/yr” and “yr” to avoid ambiguity.

 

• Questionable detection limit reporting: The reported limits of detection (LOD) and quantification (LOQ) raise concerns. The LOD is given as 0.08–0.17 mg/kg (which is 80–170 ng/g) and LOQ as 0.32–0.68 mg/kg (320–680 ng/g) for the PAHs. Yet the lowest measured soil PAH concentration is 24.97 ng/g, far below even the lowest LOD. This suggests a contradiction: how did they detect ~25 ng/g if their lowest detection limit was ~80 ng/g?

 

• Misidentification of PAH compounds and abbreviations: There is a mistake in the list of PAH compounds in the methods. “naphthalene (Nap), acenaphthene (Acpy), acenaphthene (Ace), ...”. Clearly, acenaphthene is listed twice with two different abbreviations. All PAH names and short codes need to be consistent across text, tables, and figures.

 

• Errors in Table 2 (parameters for risk assessment): There are a few issues in Table 2 that need correction. First, the description of IRsoil as “Soil inhalation rate (mg/d)” is incorrect. One does not inhale soil in mg/day; this is clearly meant to be soil ingestion rate (the amount of soil accidentally ingested per day). The standard notation is often IR (ingestion rate) for soil in mg/day, and some texts use “IngR” for ingestion versus “InhR” for inhalation. Here, the authors have IRsoil and IRair; IRsoil should be described as “Soil ingestion rate”. Second, the units and labeling for some parameters could be clearer. EF is given as “d/a” which presumably means days per annum (days per year). ED is given in “a”, which is non-standard as mentioned (should be years). SA is “Dermal exposure area (cm²/d)” – here “per day” is a bit confusing, since surface area is not per day, but typically one would list SA as cm² (area of skin) and not divide by day, because exposure frequency (EF) already accounts for days. The authors should check standard risk assessment parameter definitions (https://doi.org/10.3389/fenvs.2024.1370397) to ensure each parameter’s unit is correct. In addition, Table 2 calls it “Dermal adsorption parameter”. This is likely a typo: it should be absorption (not adsorption). Adsorption refers to sticking onto surfaces, whereas absorption is uptake into skin, which is the intention here. All these textual errors (ingestion vs inhalation, adsorption vs absorption) must be fixed to avoid confusion. Lastly, the authors should consider adding a brief footnote to Table 2 citing the source of these parameters (e.g., “Parameters and values from ***.

 

• Missing explanation of software

 

• Reliability of PMF results for sediment is doubtful: The PMF analysis for soils (32 samples, 16 compounds) is reasonable. However, doing PMF on only 6 sediment samples is highly questionable. PMF is a factor analysis method that generally requires a larger sample size to derive meaningful factors. With 6 samples, one can at best fit a very limited model, and the robustness of 4 factors (as they report for sediments) is suspect. Therefore, remove the sediment PMF.

 

• Source Apportionment – PMF Results Clarity: You label Factor 1 as “fossil fuel combustion,” Factor 3 as “mixed source of petroleum and fuel combustion,” Factor 4 as “coal combustion”. Then in the summary of contributions, you group “petroleum pollution and fuel combustion” together and “fossil fuel combustion” separately. This is confusing because “fossil fuel combustion” could encompass coal, diesel, etc., which seem to overlap with the other categories. It reads as if Factor 1 and Factor 4 are both fossil fuel combustion (with Factor 4 explicitly coal). Please streamline the naming. Perhaps call Factor 1 “vehicular/industrial combustion”, Factor 4 “coal combustion”, Factor 3 “petroleum (crude oil) + combustion mix”, etc., to avoid semantic overlap.

 

• Equations are not numbered and have formatting errors: In Section 2.5, none of the equations are labeled. More concerning is the formatting: the ILCR equations with a formatting issue with the term (BW/70)^…. This is meant to be a cube-root of (BW/70).

 

• ILCR parameter inconsistencies and brackets. Specifically noted “incorrect ILCR formula bracket usage” and ensure each fraction is properly bracketed, e.g. IR * EF * ED / (BW * AT * 10^6).

 

• Clarify exposure assumptions for ILCR (adults vs. children)

 

• Detection of Chrysene not discussed: In Table 3 (soil PAH stats), chrysene (Chr) was detected in only 9.38% of samples, making it one of the least detected PAHs. However, the text discussing different detection rates

 

• Typographical and grammatical issues (general polish): The manuscript needs careful proofreading for English language issues and typos.

 

• Chinese text appears on Figure 4 (must be translated).

 

• Check the number of significant figures (digits) presented in experimental results and limit them to two or three based on measurement precision. Suggest avoiding excessive decimal places for percentages (one decimal is sufficient).

 

• Omission and mis-citation of references: A number of references cited in the text (especially in tables) are missing from the reference list. For example: Zhu et al. (2014) is cited in Table 4 for Tianjin industrial soil, but there is no Zhu 2014 in the reference list (the list goes up to ref. 53 which is Zhang 2016). Likewise, Zhang et al. (2015) for Xi’an soil and Zhang et al. (2020) for Zhengzhou soil appear in Table 4, but neither is in the list, etc.

 

• Outdated references in Table 6 (sediment comparisons): Table 6 compares sediment PAH concentrations in various regions, but many of those studies are relatively old: e.g., Zhanjiang Bay and Leizhou Bay data from 2012, Mexico Gulf 2014, etc. While it’s fine to include them for a broad perspective, the authors should also seek more recent studies

 

• Remove unused or irrelevant references: Harkov & Greenberg (1985), Brown et al., 2012 are about PAHs in air. They appear unrelated to this soil/sediment study.

 

• Citing Suggested References: As part of improving the manuscript, incorporate the two additional specified references and other suggested ones into your revised text where appropriate. For instance:

https://doi.org/10.3389/fenvs.2024.1370397

https://doi.org/10.1016/j.jenvman.2024.122432

• These publications should be cited in the Introduction to highlight how the current study differs, cite in Introduction or Discussion regarding YRD PAH distribution and risk, cite to discuss PAHs in soil and sediment under the significance of PAH contamination. These specific works are recommended because they are very recent and directly relevant.

 

 

 

Author Response

Comment 1: Grid method mentioned, but no grid size given. Criteria for "less affected" areas are unclear.

Response: Thank you for your valuable comment. We have now clarified the grid size used for site selection and the criteria for identifying less anthropogenically affected areas. Specifically, a grid spacing of 6 km×6 km was applied across the study region to ensure systematic spatial sampling. Sites were selected based on their distance from potential sources of human disturbance, such as roads, settlements, cultivated fields, and industrial facilities, using both satellite imagery and on-site evaluations.

Comment 2: Were replicates combined or analyzed separately? Is intra-site variance reported?

Response: We clarified that three replicates per site were composited into a single homogenized sample for analysis. 

Comment 3: No mention of drying, grinding, sieving, etc.

Response: We have added a detailed description of the sample preparation procedure prior to extraction. This information has been incorporated at the beginning of the revised “Sample Extraction, Analysis, and Quality Control” section (Section 2.3).

Comment 4: 32 soil vs. 6 sediment samples—needs acknowledgment.

Response: Thank you for your valuable comment. To address your concern regarding the limited number of sediment samples (n = 6), we have added a cautionary statement at the end of Section 3.2 to acknowledge the potential limitations in spatial interpretation. Additionally, the Conclusion section has been revised to recommend more extensive sediment sampling in future studies to enhance spatial resolution.

Comment 5: Units like “mg/kg” vs “ng/g” are mixed; “d/a”, “a” are non-standard.

Response: Thank you for pointing out the inconsistencies in unit notation. We have thoroughly reviewed and standardized the units throughout the manuscript. Concentration units have been unified to ng/g instead of mg/kg for consistency and clarity. Time-related units have been updated to internationally accepted formats: “d/a” has been revised to “days/year”, “a” has been changed to “years”, and “d” is now consistently written as “days”.

Comment 6: LOD is 80 ng/g, yet lowest concentration reported is 25 ng/g — contradiction.

Response: Thank you for pointing this out. The unit inconsistency was due to a mistake in the original manuscript. All concentration-related values are now uniformly expressed in ng/g.  We have corrected them to the appropriate units (LOD: 0.08–0.17 ng/g; LOQ: 0.32–0.68 ng/g), and the reported concentrations in the results all exceed the LOQs.

Comment 7: “Acenaphthene” is listed twice with different abbreviations (Acpy & Ace).

Response: We have corrected the PAH list by distinguishing acenaphthylene (Acpy) and acenaphthene (Ace).

Comment 8: Mislabeling “Soil inhalation rate” instead of “ingestion”; also “adsorption” vs “absorption”.

Response: We corrected the mislabeled terms in Table 2 and adopted standard parameter definitions.

Comment 9: Only 6 samples—PMF not statistically reliable.

Response:We have removed the PMF analysis for sediment samples due to insufficient sample size.

Comment 10: Naming overlaps; "fossil fuel", "coal", "petroleum"—confusing.

Response: Thank you for the insightful comment. In the revised manuscript, we have clarified the naming of PMF factors to reduce semantic overlap and improve interpretability. Specifically, we renamed the original factors as follows:

Factor 1: “Vehicular/industrial combustion” (originally “fossil fuel combustion”),

Factor 2: “Traffic emissions”,

Factor 3: “Petroleum and biomass combustion” (originally “mixed petroleum and fuel combustion”),

Factor 4: “Coal combustion”.

Comment 11:

Response: We have added equation numbers and corrected the bracket usage and formatting errors in the ILCR model.

Comment 12: Clarify ILCR exposure assumptions (adults vs children).

Response: Thank you for your suggestion. We have clarified the exposure assumptions and parameter differences between adults and children in Section 2.5. The values of key parameters such as body weight (BW), ingestion rate (IRsoil), dermal area (SA), and exposure duration (ED) were set separately for adults and children, based on their age-specific physiological and behavioral traits. These differences are now clearly explained in the text and presented in Table 2.

Comment 13: Chr detection not discussed.

Response: We have added a note about the low detection frequency of chrysene in Section 3.1.

Comment 14: Language & grammar polish needed.

Response: The manuscript has been thoroughly proofread to correct typographical and grammatical errors.

Comment 15: Chinese text in Figure 4.

Response: All Chinese labels in Figure 4 have been translated into English.

Comment 16: Significant figures too long.

Response: We have limited the number of significant figures in the results to enhance readability and reflect appropriate precision.

Comment 17: Reference mis-citation (Zhu et al. 2014、Zhang 2015/2020 in table 4).

Response: We have reviewed and corrected all in-text citations to ensure that every cited work is included in the reference list.

Comment 18: Outdated references in sediment table 6.

Response: We have supplemented recent studies (post-2020) to improve the comparability and currency of sediment PAH data.

Comment 19: Irrelevant references (e.g. air PAH papers).

Response: We have removed references unrelated to soil and sediment PAH contamination,such as “Brown et al., 2012”. 

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The author adequately carried out the recommendations for improvement suggested above, so I have no further comments, I recommend acceptance of the manuscript.

Author Response

Comment1：The author adequately carried out the recommendations for improvement suggested above, so I have no further comments, I recommend acceptance of the manuscript.

Response1：We sincerely appreciate your positive feedback and recommendation for acceptance. Your initial suggestions greatly improved the quality of our manuscript, and we are grateful for your time and expertise.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript has been corrected according to my comments and in my opinion can be accepted for publication.

Author Response

Comment1：The manuscript has been corrected according to my comments and in my opinion can be accepted for publication.

Response1：Thank you for your constructive comments during the review process. We have carefully addressed all your suggestions, and we are pleased that you now find the manuscript suitable for publication.

Reviewer 4 Report

Comments and Suggestions for Authors

In my previous review, I recommended that the authors analyze and cite the reference https://doi.org/10.3389/fenvs.2024.1370397. As a result of the authors' failure to consider the suggested publication, the revised manuscript contains incorrect units for PAH concentrations in equations (2)–(6) related to health risk. These incorrect units may lead to discrepancies of several orders of magnitude in the calculated risk index values. This is not a minor issue! For example, a similar mistake recently led the reputable journal Chemosphere to lose its impact factor: https://arstechnica.com/health/2024/12/huge-math-error-corrected-in-black-plastic-study-authors-say-it-doesnt-matter/.

Author Response

Comment1：In my previous review, I recommended that the authors analyze and cite the reference https://doi.org/10.3389/fenvs.2024.1370397. As a result of the authors' failure to consider the suggested publication, the revised manuscript contains incorrect units for PAH concentrations in equations (2)–(6) related to health risk. These incorrect units may lead to discrepancies of several orders of magnitude in the calculated risk index values. This is not a minor issue! For example, a similar mistake recently led the reputable journal Chemosphere to lose its impact factor: https://arstechnica.com/health/2024/12/huge-math-error-corrected-in-black-plastic-study-authors-say-it-doesnt-matter/.

Response1：Thank you for your constructive comments which has significantly improved the accuracy of the article and the research. We have cited the recommended literature, and after careful study, we have modified the units in the health risk assessment formula of this article based on the content of the literature. We have also verified the calculation results.