Enhanced Adsorption and Biomineralization of Cadmium and Arsenic in Irrigation Water by Biological Soil Crusts: The Key Roles of Iron/Manganese and Urea

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper provided novelty and important information about remediating As and Cd co-contaminated paddy fields. The experiments were well designed and the results were clearly discussed and some figs were hard to understand. In all, this paper is recommended for minorrevisions. 

Several minor problems and suggestions are shown below:

1.There are some grammatical problems in this manuscript that need to be checked and modified in the whole text. 

2.The authors ought to go into great detail on the pH and redox potential in relation to the impacts of phytotoxicity and bioavailability.

3. Please also write some toxic effects of Cd and As in the introduction part.4. “With the fast development of industrialization and urbanization, in many parts of Asia(e.g. Bangladesh, India, etc.),” as it is Chinese study, so must mention the name of China.

5. references are very old, I suggest to the author please cite latest articles.

Author Response

1. Comment: There are some grammatical problems in this manuscript that need to be checked and modified in the whole text.                                                                                                 Response: Many thanks to the reviewers for their professional opinions. We have reviewed and polished the main content of the manuscript as a whole, and corrected grammatical errors, inaccurate and unprofessional words, and some expressions that are easy to be misunderstood by readers. The certificate of the grammatical corrections is provided.

 

2. Comment: The authors ought to go into great detail on the pH and redox potential in relation to the impacts of phytotoxicity and bioavailability.                                                                           Response: Thanks a lot for your professional comments. We have supplemented the pH and redox potential in relation to the impacts of phytotoxicity and bioavailability“It has been shown that Cd converts from a highly bioavailable form to a less bioavailable form as pH increased and Eh decreased[30]. While As happens to be the opposite of Cd, the decrease in pH and the increase in Eh under the action of Fe/Mn can make As(III) more transformed to As(V), thus reducing the toxicity of As[31]. Therefore, when using Fe/Mn and urea to assist BSC remediation of As and Cd contamination in solution, further research should be carried out on the appropriate pH and Eh environments to reduce the hazards of As and Cd.”(line 186-191）

 

3. Comment: Please also write some toxic effects of Cd and As in the introduction part.           Response: Thanks for your professional comment. We have supplemented some toxic effects of Cd and As “Excessive amounts of As and Cd in the soil disrupt the metabolism and normal physiological functions of rice leading to poor plant growth and a reduction in yield[5].”(line 45-48)

“It is also reported that As can generate Reactive Oxygen Species (ROS), which will cause further damage to macromolecules such as lipids, proteins, and DNA[7]. Cd causes intestinal oxidative stress, inflammation and intestinal and Cd also disrupts the intestinal microbiota, affecting its structure, taxonomic composition and metabolic functions[8].”(line 49-54)

 

4. Comment:  “With the fast development of industrialization and urbanization, in many parts of Asia(e.g. Bangladesh, India, etc.),” as it is Chinese study, so must mention the name of China.   Response: The reviewer’s suggestion has been adopted. We have added the name of China.(line 40)

 

5. Comment: references are very old, I suggest to the author please cite latest articles         Response: The reviewer’s suggestion has been adopted. Authors cited latest articles in the paper.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This work introduced that the biological soil crust was used to deal with Cd and As pollution, and  it is an interesting research.  However, there are some points needed to be revised, including poor writing result and discussion, and rough figtures. Thus, I think this manuscript should be rejected.

1. Abstract should be reorganized and more discussion should be added.

2.  Introduction section should be modified due to poor logic. There are many sources of heavy metal polltion, but authors only stated this sentence,  " With the rapid development of industrialization and urbanization, in many parts of Asia" . It is unreasonable. In addition, the review of BSC is inequacy.

3. A table should be added in 2.2 section, and distribution in 2.3 is not suitable, should be modified as Cd and As species distribution.

4. There is no error bar in figures, and no difference analysis for data in Fig4-9. 

5. More discussion should be given, and  the mechenism of BSC adsorb As and Cd should be considered.

6. Chemical formula were spelling mistake in this paper.

7. In addition, I suggest author rewrite the conclusion to make this work get better summary.

 

Comments on the Quality of English Language

Please check the English grammar, and modify it, and native English speakers should be requested to help modify.

Author Response

1. Comment: Abstract should be reorganized and more discussion should be added.            Response: We are grateful for the suggestion. As suggested by the reviewer, we have added the discussion“It has been shown that Cd converts from a highly bioavailable form to a less bioavailable form as pH increased and Eh decreased[30]. While As happens to be the opposite of Cd, the decrease in pH and the increase in Eh under the action of Fe/Mn can make As(III) more transformed to As(V), thus reducing the toxicity of As[31]. Therefore, when using Fe/Mn and urea to assist BSC remediation of As and Cd contamination in solution, further research should be carried out on the appropriate pH and Eh environments to reduce the hazards of As and Cd.（line 186-191）”

“It has been shown that the organic matter in EPS contains a large number of amide, hydroxyl and other functional groups, which play a significant role in the adsorption of heavy metals[41].”(line 262-264)

“In the case of EDTA, which can chelate the Cd by ligand complexes that can effectively increase the mobility and translocation of Cd[43]. In contrast, the fraction that cannot be extracted by EDTA is relatively stable.”（273-275）

“However, at lower Mn(II) concentrations (0-0.4 mM), Mn(II) promoted cadmium immobilization, while at higher Mn(II) concentrations (0.6-1.0 mM), this effect was diminished[49]”（293-295）

 

2. Comment: Introduction section should be modified due to poor logic. There are many sources of heavy metal polltion, but authors only stated this sentence,  " With the rapid development of industrialization and urbanization, in many parts of Asia" . It is unreasonable. In addition, the review of BSC is inequacy.                                                                                                         Response: Thanks for your professional comment. We have supplemented sources of heavy metal pollution “Moreover，As may accumulate in agricultural soils due to the agricultural practices such as the applications of As-containing pesticides and herbicides, pig manure, and phosphorous fertilizers[3].”(line42-44)

 

 

3. Comment: A table should be added in 2.2 section, and distribution in 2.3 is not suitable, should be modified as Cd and As species distribution.                                                                              Response: The reviewer’s suggestion has been adopted. We have added the Table 1(line 132-133)

 

4. Comment: There is no error bar in figures, and no difference analysis for data in Fig4-9. Response: Thank you for the above suggestions. The error lines on the graphs have been added and the analysis of variance is reflected in the article.

 

5. Comment: More discussion should be given, and the mechenism of BSC adsorb As and Cd should be considered.                                                                                                                      Response: Thanks for your professional comment. We have added the mechenism of BSC adsorb As and Cd in the discussion.

 

 

6. Comment: Chemical formula were spelling mistake in this paper.                                            Response: We are very sorry for our incorrect writing. We've modified in the article.

 

7. Comment: In addition, I suggest author rewrite the conclusion to make this work get better summary.                                                                                                                             Response: Thanks very much for your kind suggestion. We rewrite the conclusion.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript presents a thorough study on the adsorption and biomineralization of Cd and As in irrigation water using biological soil crusts (BSC). By investigating the effects of additional Fe/Mn and urea on the remediation efficiency of BSC, the study addresses critical issues related to agricultural sustainability and water quality. The comprehensive experimental design and results contribute valuable insights to the field of bioremediation.

While the manuscript is well-structured and provides significant insights, some areas could benefit from further clarification and elaboration. Enhancing the depth of discussion on the mechanisms driving the results, as well as addressing the scalability and practical application of BSC in agricultural systems, would strengthen the study’s relevance. Additionally, a more detailed exploration of the long-term environmental implications of Fe/Mn and urea use would further improve the manuscript's impact.

This study contributes to the field, but I recommend minor revision. These include improving the clarity and contextualization of specific sections and addressing typographical errors. Also, I suggest thorough proofreading before final submission to ensure clear understanding of the obtained findings.

1.                  The abstract provides a concise summary of the study’s aim and findings but does not clearly highlight the specific mechanisms by which Fe/Mn and urea affect As and Cd remediation. Could the authors explicitly state the novel contributions of this study compared to existing literature?

2.                  The introduction establishes the importance of addressing heavy metal contamination in rice fields effectively. Adding a brief explanation of how biological soil crusts interact with heavy metals and how this research builds on prior studies could strengthen the study's context.

3.                  The description of the experimental setup and cultivation of BSC is detailed. I suggest that authors can maybe include a schematic or flow diagram of the experimental design to improve visual clarity.

4.                  The study uses specific concentrations of Fe/Mn and urea. Were these values selected based on prior studies, preliminary experiments, or practical considerations for field applications? Clarifying this would enhance understanding.

5.                  The authors report the use of ANOVA for statistical analysis. Were assumptions such as normality and homogeneity of variance tested? If not, could additional tests, such as post-hoc analyses, be included to ensure robustness?

6.                  The observed changes in pH and Eh over time are described, but their direct implications for microbial activity and heavy metal adsorption are not fully explained. How do these shifts correlate with the effectiveness of BSC over time?

7.                  The study notes that Cd uptake improved in the presence of As in co-contaminated scenarios. Could the authors provide more detail on the underlying mechanisms or potential synergistic interactions driving this observation?

8.                  The fractional distribution of As and Cd in BSC (e.g., EPS, sorbed, non-EDTA-exchangeable fractions) is analyzed but could benefit from further discussion. What are the implications of these distributions for the long-term stability and potential remobilization of heavy metals under fluctuating environmental conditions?

9.                  While the graphs effectively present the results, the legends and axis labels could be more descriptive to enhance accessibility. For instance, replacing abbreviations like As+BSC with full terms would aid readability.

10.              The discussion suggests that Fe/Mn promotes As removal through biomineralization, while Mn competes with Cd for adsorption sites. Could the authors expand on potential strategies to mitigate such competition in practical applications?

11.              The study discusses the effects of urea on enhancing microbial activity and Cd sorption. Could the authors provide a more detailed explanation of how urea impacts microbial diversity and activity within the BSC?

12.              Variations in pH and Eh influence As and Cd removal, but the effects on their chemical speciation and bioavailability are not fully explored. Could the authors elaborate on these dynamics and their implications for remediation?

13.              Figures 4–9 present dense data that could be simplified for clarity. Have the authors considered dividing mono-contamination and co-contamination results into separate sections or graphs?

14.              A summary table of removal efficiencies for different experimental conditions (e.g., As/Cd concentrations, Fe/Mn or urea levels) could provide readers with a clearer comparison of outcomes.

15.              The study concludes that BSC is a promising tool for heavy metal remediation. However, scaling up this method for field applications may pose challenges. Could the authors discuss potential obstacles, such as cost, maintenance, and ecological trade-offs?

16.              Fe/Mn and urea are common agricultural inputs. How do the authors envision integrating their findings into existing farming practices while minimizing environmental risks, such as ammonia or nitrogen loading?

17.              The study focuses on controlled laboratory conditions. How might variability in natural BSC composition or environmental factors (e.g., temperature, soil conditions) affect scalability and effectiveness in field applications?

18.              The long-term effects of urea-induced pH changes on BSC stability and heavy metal re-release are not addressed. Could the authors assume outcomes of prolonged exposure to these conditions?

19.              Given the observed limitations, such as the competition between Mn and Cd or the inhibitory effects of urea on As removal, what additional research directions do the authors recommend for optimizing BSC-based remediation?

20.              Did the authors think about exploring the potential for integrating BSC with other bioremediation methods, such as microbial consortia or plant-based techniques, to enhance overall effectiveness in complex contamination scenarios?

Author Response

1. Comment: The abstract provides a concise summary of the study’s aim and findings but does not clearly highlight the specific mechanisms by which Fe/Mn and urea affect As and Cd remediation. Could the authors explicitly state the novel contributions of this study compared to existing literature?                                                                                                                                     Response: Thanks a lot for your professional comments. We have added the the specific mechanisms by which Fe/Mn and urea affect As and Cd remediation in the abstract (line 30-32).

 

2. Comment: The introduction establishes the importance of addressing heavy metal contamination in rice fields effectively. Adding a brief explanation of how biological soil crusts interact with heavy metals and how this research builds on prior studies could strengthen the study's context.                                                                                                                          Response: Thanks for your professional comment. We have supplemented a brief explanation of how biological soil crusts interact with heavy metals “On the one hand, BSC adsorb heavy metals through their own surface chemistry, and on the other hand, the biological components of BSC will reduce the concentration of heavy metals through adsorption or photosynthesis[21].”(line 81-83)

 

3. Comment: The description of the experimental setup and cultivation of BSC is detailed. I suggest that authors can maybe include a schematic or flow diagram of the experimental design to improve visual clarity.                                                                                                                         Response: We gratefully appreciate your valuable suggestion. We have added the Table 1(line 132-133)

 

4. Comment: The study uses specific concentrations of Fe/Mn and urea. Were these values selected based on prior studies, preliminary experiments, or practical considerations for field applications? Clarifying this would enhance understanding.                                                          Response: Thank you for your rigorous consideration. The specific concentrations of Fe/Mn and urea referenced from previous article (Reference 48).

 

5. Comment: The authors report the use of ANOVA for statistical analysis. Were assumptions such as normality and homogeneity of variance tested? If not, could additional tests, such as post-hoc analyses, be included to ensure robustness?                                                                                     Response: We used normality and homogeneity of variance tested by SPSS.

 

6. Comment: The observed changes in pH and Eh over time are described, but their direct implications for microbial activity and heavy metal adsorption are not fully explained. How do these shifts correlate with the effectiveness of BSC over time?                                                 Response: Thank for your comments. On the one hand, changes in pH and Eh directly affect the concentration and morphology of As and Cd in solution; on the other hand, BSC is composed of a variety of algae and microorganisms, which are susceptible to environmental influences, and the increase in pH over time affects the activity of BSC, thereby reducing the adsorption of heavy metals by BSC

 

7. Comment: The study notes that Cd uptake improved in the presence of As in co-contaminated scenarios. Could the authors provide more detail on the underlying mechanisms or potential synergistic interactions driving this observation?                                                                           Response: Thanks for your professional comment. It has been supplemented in the literature “Electrostatic attraction, surface complexation, and formation of type A (the metal is near the surface) or type B (the ligand is near the surface) ternary surface complexes were considered as the main mechanisms that the adsorption of metal cations can be enhanced by the present of anions[38]” therefore Cd uptake improved in the presence of As in co-contaminated scenarios. (line233-236)

 

8. Comment: The fractional distribution of As and Cd in BSC (e.g., EPS, sorbed, non-EDTA-exchangeable fractions) is analyzed but could benefit from further discussion. What are the implications of these distributions for the long-term stability and potential remobilization of heavy metals under fluctuating environmental conditions?                                               Response: We totally understand the concerns of the reviewer. We mentioned in the manuscript that metals distributed in the non-EDTA exchangeable fraction either accumulate in the cells or adsorb in the inorganic solid phase. This also suggests that it is difficult for non-EDTA exchangeable fraction heavy metals to re-release the environment

 

9. Comment:  While the graphs effectively present the results, the legends and axis labels could be more descriptive to enhance accessibility. For instance, replacing abbreviations like As+BSC with full terms would aid readability.                                                                                                Response: Thank you for your comments. In the Materials and methods, we have detailed what the various abbreviations in the manuscript represent.

 

10. Comment: The discussion suggests that Fe/Mn promotes As removal through biomineralization, while Mn competes with Cd for adsorption sites. Could the authors expand on potential strategies to mitigate such competition in practical applications?                                              Response: Thanks very much for your question. This is indeed a scientific question that needs further research. In the revision，we added the discussion in line 294-296“However, at lower Mn(II) concentrations (0-0.4 mM), Mn(II) promoted cadmium immobilization, while at higher Mn(II) concentrations (0.6-1.0 mM), this effect was diminished”.

 

11. Comment: The study discusses the effects of urea on enhancing microbial activity and Cd sorption. Could the authors provide a more detailed explanation of how urea impacts microbial diversity and activity within the BSC?                                                                                        Response: We have revised the original comments to “In addition, the presence of urea provides a large amount of N, which favors BSC growth and development[55]”（line 330-331）

 

12. Comment: Variations in pH and Eh influence As and Cd removal, but the effects on their chemical speciation and bioavailability are not fully explored. Could the authors elaborate on these dynamics and their implications for remediation?                                                          Response: Thanks a lot for your professional comments.We have supplemented the content“It has been shown that Cd converts from a highly bioavailable form to a less bioavailable form as pH increased and Eh decreased[30]. While As happens to be the opposite of Cd, the decrease in pH and the increase in Eh under the action of Fe/Mn can make As(III) more transformed to As(V), thus reducing the toxicity of As[31]. Therefore, when using Fe/Mn and urea to assist BSC remediation of As and Cd contamination in solution, further research should be carried out on the appropriate pH and Eh environments to reduce the hazards of As and Cd.（line187-192）.

 

13. Comment: Figures 4–9 present dense data that could be simplified for clarity. Have the authors considered dividing mono-contamination and co-contamination results into separate sections or graphs?                                                                                                                                           Response: Thank you for your comments. It does currently separate, with Fig.4a and b showing the removal of As and Cd under As and Cd mono-contamination conditions, respectively, and Fig.5a and b showing the removal of As and Cd under As and Cd co-contamination conditions, respectively.

 

14. Comment: A summary table of removal efficiencies for different experimental conditions (e.g., As/Cd concentrations, Fe/Mn or urea levels) could provide readers with a clearer comparison of outcomes.                                                                                                                                       Response: Summary tables of removal efficiencies for different experimental conditions were supplemented in support information.

 

15. Comment: The study concludes that BSC is a promising tool for heavy metal remediation. However, scaling up this method for field applications may pose challenges. Could the authors discuss potential obstacles, such as cost, maintenance, and ecological trade-offs?                 Response: Thanks for your professional comment. We added the relevant content in line 343-344.

 

16. Comment:  Fe/Mn and urea are common agricultural inputs. How do the authors envision integrating their findings into existing farming practices while minimizing environmental risks, such as ammonia or nitrogen loading?                                                                                         Response: We totally understand the reviewer’s concern. First of all, BSC is naturally present in farmland, and chemicals such as urea are indispensable to agricultural work. The presence of BSC not only serves to remove heavy metals, but also fixes nitrogen fertilizer and maintains soil fertility.

 

17. Comment: The study focuses on controlled laboratory conditions. How might variability in natural BSC composition or environmental factors (e.g., temperature, soil conditions) affect scalability and effectiveness in field applications?                                                                         Response: We totally understand the reviewer’s concern. First, BSC grows naturally in rice fields. It is also confirmed in this manuscript that the adsorbed heavy metals are mainly distributed in the non-EDTA exchangeable state, which also indicates that it is difficult to release heavy metals into the environment after adsorption of heavy metals
18. Comment: The long-term effects of urea-induced pH changes on BSC stability and heavy metal re-release are not addressed. Could the authors assume outcomes of prolonged exposure to these conditions?                                                                                                                           Response: We totally understand the reviewer's concern. We'll continue to do research on this.

 

19. Comment: Given the observed limitations, such as the competition between Mn and Cd or the inhibitory effects of urea on As removal, what additional research directions do the authors recommend for optimizing BSC-based remediation?                                                                      Response: Thank you for your question. In future research, we think we should find a suitable chemical or precise chemical input to assist BSC to achieve simultaneous remediation of arsenic-cadmium composite pollution

 

20. Comment: Did the authors think about exploring the potential for integrating BSC with other bioremediation methods, such as microbial consortia or plant-based techniques, to enhance overall effectiveness in complex contamination scenarios?                                                         Response: Thanks a lot for your professional comments. Yes, we really think about exploring the potential for integrating BSC with microbial consortia to enhance overall effectiveness in complex contamination scenarios in further research.

 

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

 

The article presents a comprehensive and timely study on the use of Biological Soil Crusts (BSC) for the remediation of arsenic (As) and cadmium (Cd) contamination in irrigation water. Given the growing concerns over heavy metal pollution in agricultural systems and its severe health implications, this research addresses a critical environmental and public health issue. The study employs a well-structured experimental approach to investigate the effects of iron/manganese and urea on the adsorption and biomineralization capacities of BSC. The findings provide valuable insights into sustainable and eco-friendly methods for mitigating heavy metal contamination in paddy fields. However, the article would benefit from major revisions to improve clarity, elaborate on mechanisms, and enhance the presentation of results for broader applicability.

11.     [P1 L17, 34]. Suggest rephrasing for clarity and conciseness. For example, instead of "providing a green and efficient means of remediating As and Cd co-contaminated paddy fields," use "offering an eco-friendly strategy for remediating As and Cd in paddy fields."

22.     [P2 L41, 48]. Consider combining sentences to avoid repetition, e.g., "Due to industrialization, the use of heavy metal-contaminated irrigation water has led to significant As and Cd accumulation in rice, posing severe health risks."

33.     [P2 L5].  Define "periphyton" more clearly for readers unfamiliar with the term.

44.     [P3 L99, 100]. Provide more detail on how BSC was confirmed to be "mature" and what parameters determined its "deep green hue."

55.     [P3 L103, 118]. Clarify why the specific concentrations of Fe/Mn and urea were chosen for the study. Were these based on prior research or preliminary experiments?

66.     [P6 L175, 185].  the competition mechanism for binding sites between Mn and Cd needs more elaboration. Include references or supporting data for this explanation.

77.     [P7 L204, 214]. explain why the presence of As improved Cd adsorption by BSC. A mechanistic hypothesis would strengthen this section.

88.     [P9-8 L244, 250]. Provide more detail on why heavy metals in the non-EDTA-exchangeable fraction are more stable and harder to release. This is critical for understanding the long-term environmental implications.

99.     [P10 L305, 314]. The conclusion should emphasize practical recommendations for applying the findings in agricultural fields. Consider adding a short paragraph discussing potential limitations of using BSC in real-world conditions, such as scalability or cost. Compare findings with similar studies to provide context and validate the study’s approach.

110.  Materials and methods supplement the study area

111.  Result and Discussion The results should be written separately from the discussion, and the main part of the discussion should be the comparison with the previous researchers' results

112.  Conclusion，Quantitative content should be added to the conclusion, not just verbal description.

 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

1. Some sentences are overly long or complex, making them difficult to follow. Simplify sentence structures where possible (e.g., Lines 41–48).

2. Use more precise terminology to convey ideas succinctly. For instance, replace "providing a green and efficient means" (Line 33) with "offering an eco-friendly method."

Author Response

1. Comment: [P1 L17, 34]. Suggest rephrasing for clarity and conciseness. For example, instead of "providing a green and efficient means of remediating As and Cd co-contaminated paddy fields," use "offering an eco-friendly strategy for remediating As and Cd in paddy fields." Response: Considering the Reviewer’s suggestion, we have revised the original comments to“offering an eco-friendly strategy for remediating As and Cd in paddy fields.”(line 32-33)

 

2. Comment:[P2 L41, 48]. Consider combining sentences to avoid repetition, e.g., "Due to industrialization, the use of heavy metal-contaminated irrigation water has led to significant As and Cd accumulation in rice, posing severe health risks."                                                   Response: Considering the Reviewer’s suggestion, we have revised the original comments to “Due to industrialization and urbanization, in many parts of Asia(e.g. Bangladesh, India, China etc.), the use of heavy metal-contaminated irrigation water has led to significant As and Cd accumulation in rice, posing severe health risks”(line 40-42)

 

3. Comment:[P2 L5]. Define "periphyton" more clearly for readers unfamiliar with the term.    Response: Thanks a lot for your professional comments. We have supplemented the brief statement to periphyton “was originally defined as living micro-plant communities attached to submerged surfaces”(line61-62)

 

4. Comment:[P3 L99,100]. Provide more detail on how BSC was confirmed to be "mature" and what parameters determined its "deep green hue."                                                                                   Response: Thank you for your comments. Cultivation of BSC and how to determine BSC maturation are referenced in the previous research (Reference 24).

 

5. Comment:[P3 L103,118]. Clarify why the specific concentrations of Fe/Mn and urea were chosen for the study. Were these based on prior research or preliminary experiments?                            Response: Thank you for your rigorous consideration. The specific concentrations of Fe/Mn and urea referenced from previous articles(Reference 48).

 

6. Comment:[P6 L175, 185]. The competition mechanism for binding sites between Mn and Cd needs more elaboration. Include references or supporting data for this explanation.                             Response: Thanks a lot for your professional comments. We have supplemented the data and references “However, at lower Mn(II) concentrations (0-0.4 mM), Mn(II) promoted cadmium immobilization, while at higher Mn(II) concentrations (0.6-1.0 mM), this effect was diminished[49].”（line 294-296）

 

7. Comment:[P7 L204, 214]. explain why the presence of As improved Cd adsorption by BSC. A mechanistic hypothesis would strengthen this section.                                                            Response: Thank you for your comments. We have supplemented why the presence of As improved Cd adsorption by BSC “As(III) adsorbed on the composite could provide new adsorption active sites for capturing Cd(II)[37]” therefore Cd adsorption was significant enhanced by As. (line232-233)

 

8. Comment:[P9-8 L244,250]. Provide more detail on why heavy metals in the non-EDTA-exchangeable fraction are more stable and harder to release. This is critical for understanding the long-term environmental implications.                                                                                          Response: Thanks a lot for your professional comments.We have supplemented why heavy metals in the non-EDTA-exchangeable fraction are more stable and harder to release“ In the case of EDTA, which can chelate the Cd by ligand complexes that can effectively increase the mobility and translocation of Cd[43]. In contrast, the fraction that cannot be extracted by EDTA is relatively stable.”(line274-278)

 

9. Comment:[P10 L305,314]. The conclusion should emphasize practical recommendations for applying the findings in agricultural fields. Consider adding a short paragraph discussing potential limitations of using BSC in real-world conditions, such as scalability or cost. Compare findings with similar studies to provide context and validate the study’s approach.                                            Response: Thank you for the above suggestions. We have supplemented content“There is an adsorption–desorption process for the remediation of heavy metals by BSC, and further research is needed to determine when heavy metals are resolved from BSC during actual use.”(line 343-345)

 

10. Comment: Materials and methods supplement the study area                                                      Response: Thanks a lot for your professional comments. We have supplemented the study area “The soil used in the experiment was obtained from the Nongcui Park of Anhui Agricultural University(31°51.6′N, 117°16.2′E).”(line 101-102)

 

11. Comment: Result and Discussion The results should be written separately from the discussion, and the main part of the discussion should be the comparison with the previous researchers' results    Response: Thanks very much for your suggestions. The results and discussion part have been optimized and the language have been polished.

 

12. Comment: Conclusion，Quantitative content should be added to the conclusion, not just verbal description.                                                                                                                                   Response: Thanks very much for your suggestions. Quantitative content was added in the conclusion. (Line 341-342)

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

（1）The purpose and main content of the this research should be added at the end of introduction.

(2)Differential analysis results should be added in Fig.4 and Fig.5.

Author Response

（1）The purpose and main content of the this research should be added at the end of introduction.

We are deeply grateful to the reviewers. We have added the purpose and main content of this research“In order to understand the roles played by Fe/Mn and urea in the process of BSC remediating As and Cd contaminated water. The experiment simulated different heavy metal pollution conditions to explore the removal rates of As and Cd by BSC in the presence of Fe/Mn and urea.”

(2)Differential analysis results should be added in Fig.4 and Fig.5

We are deeply grateful to the reviewers. We have added Differential analysis results in Fig.4 and Fig.5.

Reviewer 4 Report

Comments and Suggestions for Authors

 

The revised manuscript shows significant improvement, addressing key issues from the earlier review. The authors have clarified the structure, detailed the methods, and presented results with clear visualization and meaningful discussions. The study highlights the potential of biological soil crusts (BSC) for dual remediation of arsenic (As) and cadmium (Cd) in irrigation water, focusing on the effects of Fe/Mn ions and urea. While well-written and methodologically sound, sections like the introduction, discussion, and conclusion could benefit from further refinement to enhance clarity, depth, and contextual emphasis.

1.     L53–L57, expand on how existing remediation techniques fall short for As-Cd co-contamination.

2.     L75–L81, briefly summarize the specific novelty of the research.

3.     L112–L127, add a rationale for the selected concentrations and explain why nine treatment groups were necessary.

4.     the conclusion effectively summarizes findings but does not sufficiently emphasize the study's broader implications or limitations.

A.    Add a sentence on broader relevance.

B.    acknowledge limitations more explicitly.

C.    compare your findings with other relevant studies.

Comments for author File: Comments.pdf

Author Response

1. L53–L57, expand on how existing remediation techniques fall short for As-Cd co-contamination.

We sincerely thank the reviewer for the meticulous review and valuable suggestions. We have added the content “Traditional methods cannot be widely applied to the remediation of As and Cd co-contaminated soils either because they damage soil quality or due to their excessively high application costs.”

2. L75–L81, briefly summarize the specific novelty of the research.

We are deeply grateful to the reviewer. We have added the the specific novelty of the research“In order to understand the roles played by Fe/Mn and urea in the process of BSC remediating As and Cd contaminated water.”

3. L112–L127, add a rationale for the selected concentrations and explain why nine treatment groups were necessary.

Thanks very much for the reviewer’s suggestion. We added the rationale for the selected concentrations and explain the necessary of nine treatment.

 

4. the conclusion effectively summarizes findings but does not sufficiently emphasize the study's broader implications or limitations.
5. Add a sentence on broader relevance.
6. acknowledge limitations more explicitly.
7. compare your findings with other relevant studies.

We are very grateful to the reviewers for their comments and have revised the original content to “Previous studies have also confirmed the remediation ability of BSC for heavy metals. However，there is an adsorption–desorption process for the remediation of heavy metals by BSC, additionally, Fe/Mn and urea still have significant limitations in the BSC remediation of As/Cd.. The results provide a natural, efficient and sustainability method for capturing As and Cd and demonstrate that BSC can have an enormous impact on the remediation of irrigation water contaminated with As and Cd. It helps to improve environmental quality more widely in various ecosystems.”