Influence of Phosphogypsum Waste on Rainwater Chemistry in a Highly Polluted Area with High Mortality Rates in Huelva Metropolitan Area, Spain

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript titled "Influence of Phosphogypsum Waste on Rainwater Chemistry in a Highly Polluted Metropolitan Area with High Mortality Rates in Spain" has been thoroughly reviewed. The study addresses an important environmental issue, providing insights into the impact of phosphogypsum waste on rainwater composition and highlighting potential environmental and health implications. Below is a detailed section-by-section review with suggestions to enhance the manuscript.

 

Abstract

The abstract is well-structured but contains minor language issues:

Replace "We estimated the impact of phosphogypsum stacks on rainwater chemical profile..." with "This study evaluates the impact of phosphogypsum stacks on the chemical composition of rainwater..."

Simplify "An enrichment of potentially toxic metal(loid)s such as..." by listing fewer elements or summarizing as "various toxic metal(loid)s."

Conclude the abstract with a stronger emphasis on the practical implications of the findings.

Introduction

The introduction effectively outlines the environmental challenges and health concerns associated with phosphogypsum waste. However:

Some sentences are overly complex and verbose. For instance, "Huelva metropolitan area lies on this Odiel–Tinto Estuary, which is recognised as one of the most heavily polluted sites in the world..." can be simplified.

Clearly highlight the novelty of this study compared to prior research on similar topics.

Avoid redundancy, particularly when discussing the sources of pollution and their impacts on health.

Materials and Methods

The methodology is detailed and thorough, but the following improvements can be made:

Provide a clearer rationale for the selection of sampling sites and their spatial distribution.

The description of the Hellman rain gauges could be shortened or moved to supplementary material.

Justify the use of specific analytical techniques, such as ICP-MS and ion chromatography, for assessing trace elements and ions.

Results

The results are presented systematically and supported by graphs and tables. Suggestions for improvement:

Provide more detailed explanations for trends observed in pH, conductivity, and trace element concentrations across the sampling sites.

Discuss any outliers or anomalies, such as locations with unusually high or low values, and provide potential explanations.

Clarify the statistical significance of correlations, particularly when discussing the impact of proximity to phosphogypsum stacks.

Discussion

The discussion effectively links the results to the study's objectives but can be strengthened:

Compare findings with other studies to better contextualize the results.

Expand on the health implications of exceeding WHO guidelines for pH, fluoride, and nickel in rainwater.

Provide a more detailed analysis of the contribution of local and regional pollution sources, such as industrial complexes and marine factors.

Conclusion

The conclusion summarizes the findings well but could be more concise.

Emphasize the study's broader implications for environmental policy and future restoration plans, particularly the RESTORE2030 project.

 

English

The manuscript is generally well-written but would benefit from minor grammatical and stylistic edits:

Replace informal phrases like "clearly exceeded" with more formal alternatives, such as "significantly surpassed."

Ensure consistent terminology throughout the manuscript (e.g., use "phosphogypsum stacks" instead of alternating with "PG stacks").

Shorten lengthy sentences to improve readability.

 

The manuscript provides valuable insights into the environmental impact of phosphogypsum stacks, with implications for public health and restoration strategies. With minor revisions to enhance clarity, conciseness, and contextualization, it will make a strong contribution to the field.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Considering the increasing global concern about industrial waste management and its implications for human and environmental health, this topic is relevant. The study is well-structured, and the results contribute to the growing body of literature on the environmental impacts of phosphogypsum. The study used good chemical analysis techniques to evaluate rainwater composition, providing reliable data on pollutant levels and potential sources.

However, in the discussion, the following is recommended.

Since the study references high mortality rates, incorporating epidemiological data to link chemical contamination in rainwater to health outcomes directly would strengthen the study's implications. This can be done by using literature the authors claim is already there. The connection between rainwater chemistry and high mortality rates is compelling but underexplored in the paper. Providing a more detailed discussion on epidemiological data or referencing relevant studies would strengthen this link.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The English could be improved. Authors need to check grammatical errors highlighted in the manuscript.

 

Author Response

Considering the increasing global concern about industrial waste management and its implications for human and environmental health, this topic is relevant. The study is well-structured, and the results contribute to the growing body of literature on the environmental impacts of phosphogypsum. The study used good chemical analysis techniques to evaluate rainwater composition, providing reliable data on pollutant levels and potential sources.

However, in the discussion, the following is recommended.

We thank the reviewer for the positive comments. They have helped us to improve our manuscript. We have provided detailed answers to every comment, and changes have been tracked within the revision of the manuscript. We very much appreciate your time and consideration of our work.

Since the study references high mortality rates, incorporating epidemiological data to link chemical contamination in rainwater to health outcomes directly would strengthen the study's implications. This can be done by using literature the authors claim is already there. The connection between rainwater chemistry and high mortality rates is compelling but underexplored in the paper. Providing a more detailed discussion on epidemiological data or referencing relevant studies would strengthen this link.

While the main objective of our study is to ‘investigate the distribution of the suspended pollutant particles originating from the PG stacks to identify the radius of influence over the rainwater chemical fallen in Huelva metropolitan area’, there are background implications on our study to highlight its public health relevance. As the area under study is very close by to relatively high populated cities (Huelva metropolitan area counts near 300K inhabitans) and as we mention on introduction (line 36), ‘There is support on the international scientific literature for a deleterious effect for human heath due to environmental exposure to many of those metals [1,4]’. If there is ‘overall scientific’ evidence for an association between environmental pollution and specific causes of mortality in the literature associated with environmental pollution, and in Huelva we observe both, we believe that is justified to think that a causal link might be possible, even more if the Huelva estuary is heavily polluted as we mention in the next paragraph of the introduction. However, we have to be cautious, as to date, there are no reports in the literature directly linking an increase of the mortality rates with exposure to metals specifically arising from the phosphogypsum stacks. To study such objective will be a next step on our line of research. We have currently requested morbidity and mortality data to local authorities, but we have no received response yet.

We have added the following sentence at the discussion section (line 622):

“More studies are needed to link the specific contribution of metals from the phosphogypsum stacks from different sources (trophic chain, water geochemistry, direct air resuspension, dust deposition from rain) to the pollution load of the Huelva Estuary to study its association with the local morbidity and mortality.”

peer-review-43769019.v2.pdf

The PDF document attached includes all responses to the reviewer's suggestions. Moreover, all changes are included in the new version of the manuscript.

The English could be improved. Authors need to check grammatical errors highlighted in the manuscript.

We thank the reviewer for the comment. The authors sent the manuscript to Cambridge Proofreading LLC. (https://proofreading.org/) and a native English-speaking editor corrected the spelling, grammar, vocabulary and writing errors in our manuscript. As proof of this, in our reply to the first revision we enclosed the certificate issued by Cambridge Proofreading number 486-44-51.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript “Influence of Phophogypsum Waste on Rainwater Chemistry in a Highly Polluted Metropolitan Area with High Mortality Rates in Spain” reports one year observations on rain water chemistry over Huelva metropolitan area, during 2021-23. Authors found that levels of pH, F^- and Ni in a rain gauge at a nearby phosphogypsum pile significantly exceeded the WHO guidelines for drinking water quality; Authors also found that in addition to the phosphypsum pile, other sources contributed to regional sources (marine factors: Ca²⁺, Cl^-, K⁺, Mg²⁺ and Na⁺) and local sources ((chemical parks emissions: Co, Cu, Pb and Zn); The authors seek to use the findings to evaluate future remediation plans to mitigate the potential environmental and health impacts of phosphogypsum piles. However, there are still many shortcomings in this article (e.g., low quality of figures, no in-depth discussion), and the detailed problems are as follows.

1. First of all, the title has a word error: "Phophogypsum" should be corrected to Phosphogypsum".
2. The summary is concise, but it does not make clear the direct link between phosphogypsum accumulation and health effects, particularly mortality from cancer and heart disease. Research questions such as "The effect of phosphogypsum accumulation on the chemical composition of precipitation in the region and its potential health risks" can be briefly identified to enhance the precision of the target.
3. Although it is mentioned in the introduction that the effect of phosphogypsum accumulation on metals in precipitation has not been studied, the uniqueness of this study and how to fill this research gap are not explained in detail. It should be pointed out why the study of phosphogypsum accumulation on precipitation metal distribution has not been fully explored so far, and further emphasized that this study is innovative in filling this gap.
4. The paper mentions the current situation of pollution in the Huelva area and its potential impact on health, but the research question and purpose are not clearly expressed in the introduction. The authors should further clarify the core issue of this study - the specific effects of phosphogypsum dumps on the chemical composition of rainwater.
5. The introduction does not briefly introduce the research methods and data sources (such as sampling location, time, analysis indicators, etc.) in advance.
6. The language expression of the manuscript is lengthy and repetitive.
7. The innovation and contribution of the research are not outstanding. For example, the existing research results on metal pollution in Huelva region are relatively rich, and the paper should further highlight its innovative points, explain why this research is necessary, and how to fill the gaps in the existing research.
8. The introduction lacks in-depth discussion of the social and policy context. The article mentions the community's concern about phosphogypsum yards and RESTORE2030, but this section fails to adequately discuss the background of social mobilization and its impact on research.
9. The distribution of rain gauges is mentioned in section 2.1, but the spatial distribution and selection criteria of rain gauges are not discussed enough. The authors chose 17 different sampling points, but there was not enough reason to explain why these points were crucial in the study.
10. The data is not presented properly. Some data, such as rain gauge distribution and pollution source analysis, are inadequately presented in the chart to highlight the differences between different sampling sites and the impact of pollution. It is recommended to redesign the diagram.
11. Several grammatical errors and awkward phrasing exist throughout the manuscript. For example, Line 154 "PG stacks (FB) rain gauge is taken as the centre of the area affected" should be corrected to "The PG stacks (FB) rain gauge is chosen as the central point of the affected are. The paper should be properly revised to be clearly expressed and logically smooth.
12. The pollution effects of phosphogypsum dumps are not discussed in depth. The description of the study area lacks detailed analysis of the specific contaminants (e.g. metals, radioactive elements, etc.) of the phosphogypsum yard.
13. The chart is of poor quality, and Figure 1 does not effectively convey key information.
14. The characterization of rain sampling and Hellman rain gauges is lengthy and unclear.
15. Line 207. Authors should describe more on the use of digital multimeter LAQUA PC220 for pH and EC.
16. Method descriptions are unclear or lack detailed information. Although you mention the use of ICP-OES and ion chromatography systems (METROHM 883 BASIC IC PLUS) for analysis, the conditions and parameters of use of these instruments are not adequately described.
17. The discussion of "standard curve" and "detection limit" mentioned in the paper is relatively brief. In order to enhance the reliability of the data analysis section, you need to provide more details about the data processing. In addition, the paper does not explicitly mention how to evaluate bias and uncertainty in the experiment.
18. The data presented in the paper are poorly interpreted. It remains unclear how trends in pH and conductivity relate to the location of precipitation sampling points (e.g., the edges and interior of PG yards) and the potential effects of pollutants.
19. All illustrations are of poor quality and unclear.
20. The data analysis in this paper lacks in-depth discussion.
21. The comparison between some data and the existing literature is relatively simple and lacks comparative analysis. For example, the neutralization effect of sea salt on pH value was mentioned in the discussion on pH value in 4.1, but no in-depth comparison was made with existing studies, and more literature support was lacking.
22. The discussion of seasonal variations in Line 409 is brief, and in particular does not provide an in-depth explanation of why rainfall concentrations farther away from PG deposits are higher in autumn precipitation. The paper can be supplemented to strengthen the analysis of seasonal changes.
23. The effect of PG accumulation on metallic elements is mentioned in section 4.3, but not enough is said about how this phenomenon manifests in space and how it relates to distance. The author can increase the spatial analysis of the effect of PG accumulation on precipitation quality, and further elaborate the effect of distance PG accumulation on metal concentration.

24.Line 514. While the potential health effects of Ni concentrations have been mentioned, less health risk analysis has been done for other metallic elements. If available, it is recommended to supplement health risk analysis for concentrations of other metals (such as Cu, Pb, Zn, etc.).

25. Correlation analysis lacks in-depth discussion. For example, in line 501, while some elements such as Co, Cu, Pb, and Zn are positively correlated with the distance to the PG yard, you fail to elaborate on why these elements exhibit this tendency, especially how they interact with surrounding industrial activity, geographic location, or meteorological conditions.
26. Line 504. Statistical analysis (e.g., R² and p-values) is used to assess correlations between variables, but for elements with low R² values (0.01-0.18), there is a lack of adequate explanation.
27. Analysis of pollution sources is insufficient. The PG yard is a major source of pollution, but there is no detail on how the yard affects the water quality of the surrounding area through precipitation or atmospheric sedimentation.
28. Spatial variability analysis is used to reveal changes in the chemical composition of precipitation. However, the data analysis method is relatively simple and fails to fully take into account more factors affecting the chemical composition of precipitation (seasonal changes, climatic factors, etc.).
29. There are too few illustrations in this paper, and there are no other illustrations to support the discussion.
30. There are no subsections to the discussion.
31. Overall, the manuscript needed further revision both in terms of content and language.
32. The conclusion of this paper can supplement the data of the proportion of pollution sources.

Given the above issues, the present manuscript is not suitable for publication, the authors must make a very deep Major Revision. If these issues are not well addressed, then this work will be rejected.

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript titled "Influence of Phosphogypsum Waste on Rainwater Chemistry in a Highly Polluted Metropolitan Area with High Mortality Rates, Huelva Province in Spain" has undergone a second round of revisions, and the authors have successfully addressed the previously raised concerns. The study is well-structured, with a clear methodology, robust data analysis, and scientifically sound conclusions regarding the impact of phosphogypsum waste on rainwater composition.

 

Based on this revised version, the paper is suitable for acceptance with no further major revisions required. Below is a summary of final observations and minor refinements that could be made before publication.

 

Abstract

The abstract is now clear, structured, and well-balanced, summarizing the research objectives, methodology, and key findings.

Minor suggestion: The final sentence could emphasize the practical applications of the study in environmental monitoring and policy-making.

Introduction

The introduction effectively contextualizes the environmental and health concerns related to phosphogypsum waste in Huelva.

The novelty of the study is now clearly stated, and the background information is well-integrated with relevant references.

No further changes needed.

 

Materials and Methods

The methodology is well-detailed and ensures reproducibility.

Minor improvement:

The justification for the selection of 17 rain gauges is well explained, but a brief summary table listing their key characteristics (e.g., location, elevation, exposure to pollution sources) could improve clarity.

No major revisions needed.

 

Results and Discussion

The results are comprehensive, with statistically supported trends in rainwater chemistry.

The discussion successfully links findings to previous studies, reinforcing the study’s validity.

Final refinements:

Figures 2–5: Captions could be slightly expanded to highlight the key takeaways rather than just describing the data.

Trace Elements Section: The authors have improved their discussion on spatial distribution of pollutants, but a brief comparison with other polluted regions worldwide (if applicable) could further strengthen the global relevance.

Only minor stylistic improvements suggested.

 

Conclusion

The conclusion effectively summarizes key findings and highlights the environmental implications of phosphogypsum contamination.

The discussion on RESTORE 2030 is now well-integrated into the conclusion, reinforcing the study’s practical significance.

Minor refinement: The authors could add a sentence on potential follow-up studies (e.g., long-term monitoring post-restoration).

No major revisions needed.

 

Language and Readability

The manuscript is well-written, with minor grammatical issues that do not impact comprehension.

Examples of minor refinements:

"The influence of phosphogypsum stacks over rainwater quality was assessed by measuring pH and conductivity." →

Suggested revision: "The impact of phosphogypsum stacks on rainwater quality was assessed through pH and conductivity measurements."

"The results denote that the principal anthropogenic source of F- is phosphogypsum stacks." →

Suggested revision: "The findings indicate that phosphogypsum stacks are the primary anthropogenic source of F- contamination."

Only minor grammatical refinements suggested.

 

Final Recommendation

The manuscript is scientifically rigorous, methodologically sound, and well-organized. The authors have effectively incorporated the necessary revisions, and the remaining suggestions are purely editorial.

 

Recommendation: Accept as is or with minor editorial refinements before publication.

Comments on the Quality of English Language

English is good.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors' R1 version attempts to respond to reviewers' previous concerns and also makes some modification. Unfortunately, the present manuscript still falls short of the “very deep Major Revision” previously required. The main issues are as follows:

1. Although the selection basis of sampling points is supplemented, the specific quantitative analysis is not provided, and it cannot be proved that 17 sampling points can effectively cover the regional pollution gradient. For example, Fig. 1 still does not label the specific distance relationship between industrial sources and residential areas, so it is difficult to judge whether the sampling point can reasonably reflect the diffusion impact of phosphogypsum pile.
2. Instrument parameters and quality control are missing. Although some parameters of ICP-OES and ion chromatography (such as wavelength range, flow rate) are added, the specific values of key indicators (such as detection limits, recovery rates) are not explained. For example, the quality score (QS) in Table S1 is only described qualitatively, and the quantitative correlation between the scoring criteria and data quality is not provided (for example, whether there is a significant difference between the sample data of QS=1 and QS=5).
3. Weak causal inference. The source of pollution was inferred only by spatial correlation (e.g., Ni concentration negatively correlated with phosphogypsum stack distance), but other confounding factors (e.g., traffic emissions, agricultural activities) were not excluded. For example, the high Co and Cu concentrations at SJ and PU sampling points in Table S2 may come from nearby thermal power plants (mentioned in line 590 of the paper), but the contribution of various pollution sources has not been quantified by source analysis models (such as PMF).
4. Lack of health risk assessment. Although some descriptions of the health effects of metals were supplemented (e.g., reproductive toxicity of Ni), no direct link was established between rainwater chemical data and local health indicators (e.g., cancer incidence). The text mentions that "further research is needed" (line 622), but the current conclusion lacks empirical support to support the core argument of "potential health risks".
5. The quality of chart visualization still needs improvement. Although the wind rose map and administrative boundaries are added to Fig. 1, key information (such as the distance between the sampling point and the phosphogypsum pile) is still marked in text, and is not visually presented by symbol size or color gradient. It is suggested to use ArcGIS to make an interpolation map to show the spatial distribution of pollutant concentration.
6. The spatial attribution of pollution sources is fuzzy. The authors attribute high concentrations of some elements (e.g., Co, Cu) to the industrial complex (IC1/IC2), but do not provide pollution source emission inventories or meteorological transport models (e.g., HYSPLIT) to verify the dispersion path of pollutants. For example, the spatial distribution of Co in Fig. 5 and the location relationship of IC1 need more explicit geographical information support.
7. It is repeatedly mentioned that phosphogypsum contains radionuclides (e.g. 210Pb), but it is not analyzed whether its concentration in rainwater exceeds radiation safety standards (e.g. IAEA limits). This lack of critical data leads to significant gaps in health risk assessments.
8. Although the authors responded to the review comments point by point, the core issues (such as causal inference, health risk demonstration, spatial analysis methods) were not effectively addressed.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is well revised. It can be accepted now.