Arsenic Concentration, Fraction, and Environmental Implication in Fe–Mn Nodules in the Karst Area of Guangxi

Round 1

Reviewer 1 Report (New Reviewer)

Hi, 

I provided some feedback on the manuscript. it was a very interesting, captivating  and well thought out research endeavor to read and review. I made some editorial suggestions to further enhance the quality of the manuscript. Please refer to attachment!

Comments for author File: Comments.pdf

Author Response

Comments from reviewer:

• Line 79.The main soil type is red soil.(Comment: It would be very insightful if the author would give a brief chemical description of thecharacteristic of that type of soil as being the adsorbent for As).

Reply: We thank the reviewer for valuable advice and accept the suggestion. The main soil type is red soil derived from carbonate rocks with typical geological high background characteristics of As, and the area has a hot and humid tropical monsoon climate.

• Lines 120-121. Table I needs to be reported in the text after "chemical fractions".

Reply:We thank the reviewer for valuable advice, but we think that

Table 1(concentrations of elements in FMNs ) in the front and Table 3 (chemical fractions) in the back is more appropriate based on the current structure of the article.

• Line 143. We used Avantage Surface Chemical Analysis Software to analyze what?

Reply:Thank you very much for discovering this error. We apologize for this grammatical problem and have corrected it based on your suggestions.

• Line 162....iron remained in a stable range in the FMNs in the environment (Table 2). Comment: Are the authors referring to the FMNs being stable in the current matrix. The term “environment” makes the sentence convoluted.

Reply: We have deleted the phrases “ in the environment” in the new manuscript.

• Line 168.[15,28-29]Comment: why a dash between 28-29?

Reply:Thank you very much for discovering this error. We have deleted the dash between 28-29.

• Line 178.the distribution map of what? was.

Reply:Thank you very much for discovering this error. We have refined the sentence in new manuscript. In a previous study from the Morvan Region in France, the distribution map of FMNs was determined through X-ray synchrotron microfluorescence analysis, showing that As is highly correlated with Fe, and the As/Fe ratio was stable throughout the entire nodule.

• Lines 201-203. As is preferentially adsorbed in-on Fe (Mn, Al) oxides/oxydroxides via sorption and/or cepreeipitation co-precipitateed to control its attenuation and mobility. The resulting effect probably caused-bythe release of additional As into the water [19-20].

Reply:Thank you very much for discovering this error. We accepted suggestions and made changes to the manuscript. We apologize for this grammatical problem and have corrected it based on your suggestions.

• Line 230.Table 5.Comment:It should be Table 6.

Reply:Thank you very much for discovering this error. We have corrected the error in the new manuscript.

• Line 239 Solution. Comment: the dot is missing after the word "solution".

Reply:Thank you very much for discovering this error. The dot was added after the word "solution".

• Line 241.Extremely low under weakly acidic conditions (pH 6.0-8.0).Comment: Usually it is recognized to be pH0-7.0.

Reply: Thank you very much for discovering this error. We have modified the error. 

Author Response File: Author Response.doc

Reviewer 2 Report (New Reviewer)

This paper describes the arsenic concentration, fraction, and environmental implication in Fe–Mn nodules in the karst area of Guangxi. The study was conducted using pH-static extraction experiments, X-ray photoelectron spectroscopy (XPS), and sequential extraction.

The results showed that most of the As occurred as As(V) in the Fe-Mn nodules (FMNs), and As(III) only occupied a small portion. The total release amount of As from the nodules was extremely low under natural conditions (pH 6.0–8.0), whereas As dissolution increased under strong acidity and alkalinity.

The work is of proper scientific quality; it is clear and intelligible. Figures and tables are apprehensible and transparent. The authors have some publications in this field.

The manuscript is very concise but adequate for publication in the Water. The paper should be published after the authors have made some revising - I have some comments regarding the article.

1.        Abstract: This part is not well written. It is too short. This paper's significant findings and scientific novelty should be emphasized in this part.

2.        Experimental part should be expanded. More experimental data is needed (diagrams, scientific apparatus used). Relative standard deviation below 10% (please explain)??

I have no additional objections to the experimental part, the results, and the discussion.

Author Response

(1)Abstract: This part is not well written. It is too short. This paper's significant findings and scientific novelty should be emphasized in this part.

Reply:We apologize for this grammatical problem and have corrected it based on your suggestions. In addition, we have asked native English editors to polish and modify the manuscript. We add and improve the abstract content.

(2)Experimental part should be expanded. More experimental data is needed (diagrams, scientific apparatus used). Relative standard deviation below 10% (please explain)??

Reply: Your suggestion is good. We have carefully evaluated the funding and experimental conditions required to complete some supplementary work, and feel that we cannot afford this expanded scope of supplenentary research at this timel. At the same time, we feel that the scope of the current thesis can still support the argument of this article. Therefore, we recommend that the supplementary experiment be included in another follow-up paper in the future.

Calculation of the relative double difference (RD/%) is a method of controlling data quality. During the testing process, the random-based cryptographic sample insertion technique, national standards of substances, the RD/% of the data were used to assess the accuracy of the repeated results obtained using analytical methods. RD/% values were calculated using the following equations:

Where C₁ and C₂ denote the test values of the basic analysis and duplicate samples, respectively. RD/% values below 10% means that test data quality is reliable.

Author Response File: Author Response.doc

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The Authors investigate changes in concentration of As in Fe-Mn nodules taken from specific region of China. The paper is understandable. My remarks are as follows:

 1. It would be good to state how As is present in the soil. Is it natural process or industrial influence?

 2. Line 41, line 46: Formally, Pb2+, Cd2+ and other mentioned are ions. Consider using Pb(II), Cd(II), …

 3. Consider lowering the number of significant digits in some values in Table 2. For example, values such as 2325.88 ± 3519.52 suggest that the accuracy is 6 meaningful digits, which I think is not the case.

 4. Please correct the numbers of tables.

 5. Minor remarks:

a) Please correct the notation for chemical reaction (1) and (2) (arrows instead of equity sign).

b) Line 166, line 192: consider using “parentheses” instead of “brackets”,

c) Line 179: please check 0.03% - Table 4 shows 0.10% for fraction F4.

d) Line 235: FMS → FMNs?

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Arsenic concentration, speciation, and environmental implica tion in Fe–Mn nodules in the karst area of Guangxi 

Descriptive paper. Common analytical procedures used but occasionally procedures which pose questions. Informative text.

Comments:

Abstract:

Residual fraction? Explain in a short sentence.

Page 1, line 42 ff:

«Although pH control agents, such 42 as lime, fly ash, and phosphates, can be used for the stabilization of Pb, Zn, and Cd in soil, 43 As is activated by higher pH levels [11-12].»

Meaning pf this sentence?

Page 1, line 44 ff:

«iron/ferrous»

Iron/ferrous/ferric?

Section 2.3.3, line 133 ff:

Do the mentioned chemicals really remove elements (here As) from the fractions in questions? Proof? Reason why sequential extraction is used and adequate?

Page 4, line 133 ff:

«curve fitting»

Method used?

Table 1:

«F4 hematite and magnetite»

Is As adsorbed on the surface or incorporated in hematite or magnetite?

Section 3.1, line 141 ff:

Elaborate about the enrichment factors and the base the mentioned factors are compared with.$

Page 5, line 160 ff:

« As strongly correlated with iron and phosphorus (rAs–Fe = 0.985, rAs–P = 160 0.670, p < 0.01) »

Elaborate on the reason why As is correlated with phosphorus.

Table 2:

Use same unity for concentration throughout for comparison!

Page 7, line 177 ff:

« Table 3 shows the geochemical speciation of As in the FMNs, determined through 177 sequential extraction. »

The term “speciation” is usually used to describe the valance state of an element. Wrong usage of this term here.

Page 8, line 233 ff:

« The addition of phosphate con- 233 siderably increased the amount of As released into the solution throughout the entire pH 234 range studied and changed the desorption edge profile in the estuarine sediment, which 235 exhibited a V-shaped profile, with the increase in As release at acid and alkaline pH values 236 [38].»

Addition of phosphate -> chemical explanation for the feature seen?

Page 8, line 245 ff:

« Overall, compared with the corresponding soils, the enrichment factors followed the 243 order As (4.27) > Fe (2.14) > P (1.71) > Mn (1.41) > Al (0.95) > Ti (0.44) > Si (0.39) > Mg (0.28) 244 > K (0.13).»

Again: Base of comparison for enrichment?

Author Response

Please see the attachment

Author Response File: Author Response.doc

Reviewer 3 Report

The resubmitted manuscript version “water-1804054” has been checked for English and grammatical errors, with minor queries addressed by researchers however, there still exists huge errors which needs severe attention. These includes:

1)     Novelty aspect: Just claiming that arsenic was not monitored in the study region and this study contribute in determining arsenic doesn’t means novel. Novelty is something which researchers contribute to existing research. How comes, previously study has been done on various heavy metals and arsenic has been ignored. Further, detailed investigation on interaction between arsenic and Fe-Mn nodules is something which can be novel. However, if researchers are taking real soil and real study area, there might be clay, silt, sand which itself provides surface sites to arsenic. How researchers guarantee that all interactions of As are with Fe-Mn nodules only. One of the severe lacking points in the design of study.

2)     Abstract section! Just checked for English. No improvement done. Abstract is key section which provides the main the theme of any research paper, however, researchers just corrected it in terms of grammatical errors and left it as it is.

3)     As tends to be adsorbed and stably fixed by the FMNs and has approximately negligible environmental implications on the soil environment under natural pH conditions (pH 6.0–8.0). However, overacidification or alkalization of the surrounding soil environment will promote the possibilities of As release, thereby causing subsequent ecological hazards. This is something which is real fact not finding. The researchers didn’t explain it and respond towards evaluation of arsenic concentration and risk assessment, which is off course should be the main theme of study. But in that case, researchers must provide details on interaction of arsenic with Fe-Mn nodules specifically in real soil environment. It’s not easy to report such results without testing for lab based investigation and claiming it works for field level. No improvement made in such aspect in manuscript.

4)     My previous comment “(7) The researchers are talking about very strong problems of any soil contaminated with As species like Line 55-56 and Line 60-63, however, they didn’t even try to design their study based on such problem statements. This is something which can’t be tolerated in any research study and I am surprise to see such mistake in any research manuscript submitted for peer reviewing in any reputable journal” remains unaddressed.

5)     My previous comment “(9)Line 88-89! Is their specific reason of analyzing As with AFS? ICP can do it why such analysis was performed with AFS?” addressed by researchers make no sense at all. Claiming that our lab technician say so we did it is totally unjustified.

6)     My previous comment “(10)Another key question, how comes researchers change pH of soil with acid and base, it’s not water sample, majority of metals can leach down while adjusting soil pH in such pH range. Indicates design fault of study.” Saying that simulating similar condition of soil in laboratory using water as environmental compartment is unjustified. There is organic matter, microbes, nitrates, phosphates, trace metals and many other components in real soil. How all can be ignored? Serious design problem in such case. Normally for such purpose, soil incubation or microcosm experiments are done to evaluate its leaching with focus towards agricultural applications.

7)     My previous comment (12), XPS analysis results and discussion! Provide details on how to make calculations, which software has been used for determination of As(III) and As(V) percentages?

8)     Conclusion section doesn’t draw any novel findings.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Responses of researchers have been found unsatisfactory. The manuscript severely lacks scientific writing and novelty. The researchers are agreeing that there are problems and unanswered whys throughout the manuscript and further study is needed in such regard. Novelty aspects of the current study are unjustified. Claiming that incubation and microcosm experiments are conducted in the current study and reporting results inappropriately doesn't make sense at all. If it's done, can researchers share a microcosm experimental setup? This type of major error remains within the manuscript, making it unsuitable for publication.