Assessment of Fraction and Mobility of Arsenic in Soil Near the Mine Waste Dam

Round 1

Reviewer 1 Report

Summary

 

In this manuscript the authors attempt to study the effectiveness of a dam in the Gilgok mine area Hongcheon, South Korea, in controlling As transport from mine waste rock from surrounding environment. Although the authors present an interesting idea, the quality of writing and many claims made in the manuscript require significant rework. For example, the phytotoxicity test added towards the end of the manuscript was poorly articulated and presented. Per the section title ‘phytotoxicity test’ one would expect this test for plant toxicity; however, the authors claim to have used the test to evaluate the bio/phytoavailability of As, which by itself is very misleading. It got even more confusing when both phytotoxicity and phytoremediation elements were not properly addressed through this test. The authors merely tested the difference in sizes of roots and shoots of bok choy plants when grown in the collected soils, which is not an effective way to determine phytotoxicity or phytoavailability or phytoremediation. A more rigorous testing is required in sufficient replicates, to justify and support the claims made by the author. Additionally, the novelty of this work is unclear, as the authors are taking a lot of sediment, soil and water samples around the contaminated zone and conducting a lot of single phase or sequential extractions, without highlighting the takeaway message from this work. Furthermore, no attempts were directed towards connecting sustainability (the nature of this journal) to the core take away and environmental implication from this work. Other editorial issues encountered by the reviewer have also been indicated below, under the specific comments section.

 

Specific comments.

 

Title:

 

The title ‘Assessment of arsenic mobility and phytotoxicity in secondary contaminated soil by mining water dam’, is conveying the wrong message that the assessment was conducted by the dam. Please correct it for its grammar.

 

Abstract:

 

Overall, the abstract was phrased extremely poorly. Needs rework. In addition, it is recommended that the authors try to add some specific results and connect them to the big picture problem here.

 

Line 12: Rephrase this sentence. Line 14-16: ‘lots of contamination area’ is grammatically incorrect, please rephrase the sentence for its grammar. Line 14-16: The objective sounds very different from the title. Please check. Line 20: Remove ‘as well as’

 

Introduction:

 

Introduction is very poorly written. Firstly, the novelty of the study is unclear. Secondly, the authors only talk about the history of dam construction but limited efforts have been made towards discussing about the 1) scientific mechanisms that affect As mobility 2) phytotoxicity or phytoremediation of Arsenic and 3) what has been done in the past at this particular site or other similar sites in South Korea or other parts of the world.

 

Line 30: Sentence too big. Too many ideas, break the sentence into two. Line 30: Find a better word for ‘unmanaged’. Line 34: ‘Gold and As share fate’, the sentence seems incomplete. What is the fate that gold and As share? Line 35-37: Please clarify what the author is trying so say here. Indicate the difference between mine waste, mine waste rock and mine tailings. Secondly how can mine waste rock and mine tailings represent other routes and not other sources. Thirdly acid mine drainage is an outcome of leaching or dissolution, but it is not really a route by itself. What other routes is the author referring to in this sentence? Line 43-44: Break the sentence into two or rephrase the sentence to not sound choppy. Correct ‘ha’. Line 45: Change '65% of the land is made up of mountains' to '65% of the land is covered with mountains' Line 47: Reference #8 does not fit the context of this sentence. Please check. Line 48-51: Poor sentence. Too long. Line 53: Change ‘cannot’ to ‘could not be’. Line 56: Change ‘falls’ to ‘occurs’. Line 71-74: Avoid beginning the sentence with ‘and’. ‘Various angles’ sounds vague, various angles of what?

So what? The novelty of the paper is unclear.

 

Materials and Methods:

 

Figure 1 was very difficult to read. Increase font size and use better colors for labelling. Also due to lack of a topographical view a better presentation must be used to separate the low-lying areas from the upper lying areas. For example, marking the direction of the water flow can help with that.

 

Lines 78-80: Too many ‘ands’, rewrite the sentence better. Line 83: ‘Forest area’ seems like a poor labelling strategy. Avoid starting a sentence with number. Line 86: Change ‘slop’ to ‘slope’. Line 99: How was the pH of the soil measured? Please explain. Line 102: Twenty-four hours is a very long time for LOI and as I understand correctly that is not what the paper suggests as well. In the paper, they use 550^oC for 4 hours. Please check. Line 102: Pipette method? Briefly describe it. Line 117-123: Very bad sentence. Too long. Break it down and rephrase it. Line 117-123: Justify why the sequential extractions were conducted, the use of acidic pHs (it is currently implicit, state it explicitly here) and how the reagents used are of any environmental relevance. Line 124-125: It reads very speculative and seems like the authors are having very little confidence in their results. Rephrase for emphasis. Line 130-131: Bioavailability tests have different purposes, clarify the purpose for the test in this particular investigation. Line 131-132: Again, starting with a number. Also why was such a mixed solution used? What purpose does it serve? Does pH 2.3 really favor bioavailability? Line 145: How is this a control? Explain why was the use of an uncontaminated soil not considered? Line 158-159: Please rephrase this sentence. It does not make sense how it reads currently. Line 159: New abbreviation ‘SAS’. Introduce its full form before abbreviating it.

 

 

Results and discussion:

 

Lines 164-166: Why could this not be the pH of rainwater? which is typically acidic (5-6) Also why do the authors think it is due to leaching? what in the leach is causing the decrease in pH? Line 166-168: This does not justify why the pH of the mine rock is more acidic? Please check. Line 169: Avoid starting the sentence with an abbreviation ‘F’. Line 171-172: Remove this sentence “For this reason, organic matter flowing into the topsoil at F area might be also low”. Line 196: Change ‘dye’ to ‘due’. Line 206: Why diffusion specifically? Do the authors think the movement is diffusion limited? If so why? Line 214: Correct grammar here. Line 215: Avoid starting the sentence with a number. Line 216: I am confused, is MF a sum of fraction 1 2 and 3 or just 1 and 2. Stick to one that is accurate, if not provide more context as to why it was changed. Line 221-222: Lost to the bottom of what? Line 222: The authors should be less indirect and more direct in their writing style. Line 224-227: Too long, break the sentence into two. Line 224-225: The soil is not bound to the arsenic; it is the other way around. Please correct it. Line 225: River and which sediments? Be specific. Line 226-227: “long time to form and inner sphere complex...” This sentence does not make sense. Please check. Line 257: Which both soils? Line 260: Define and distinguish between geogenic and anthropogenic here. Line 264: Remove the ‘be’. Line 275: Missing a full stop after aging. Line 277: Total amount of what in the soil?

 

The phytotoxicity test makes very little sense. The authors talk about toxicity test and phytoremediation, but no attempts to measure the arsenic concentrations in the plants that talk about bioavailability or phytoremediation, was made. The authors have merely based their argument based on the length of the shoots and roots. Also, how many replicates of these roots plant samples were conducted per soil? If these results are in triplicates (the error bars are missing), we can certainly consider the size of the roots and shoots as one of the factors. However, there should be other factors that should be taken in account which have clearly not been done here. 

 

Line 297: If acidic pH is affecting the growth in soils R2, 4 and 6, then how is there growth in F12 where the pH is lower. Seems contradictory. Line 306: Be specific, what characteristics are the author referring to?

 

Figures:

 

None of the figures seemed to have an error bar. If they do not, repeatability of the data/data analysis remains in question.

 

Comments for author File: Comments.pdf

Reviewer 2 Report

Dear Authors,

Please see below the comments and suggested revisions concerning the article “"Assessment of arsenic mobility and phytotoxicity in  secondary contaminated soil by mining waste dam". Manuscript Number: Sustainability-692085

REVIEW

Summary

In this paper the authors aim at assessing and confirming the effect of a dam for preventing the loss of mine waste rock containing high concentrations of arsenic on the surrounding environment and to evaluate their impacts using chemical and biological assessment. Different extraction methods were applied in the framework of the chemical assessment and phytotoxicity test was also conducted for biological assessment.

General comments

The paper is well structured. It addresses an important issue. It is widely known, that apart from natural sources arsenic contamination of water and soil resulted from human activities may pose risk. Arsenic is usually considered to be an essential element but a lot of arsenic compounds are toxic.

Therefore, I really miss the more detailed presentation of the factors influencing the mobility and phytotoxicity of arsenic. This would have been extremely important both in the introduction part and in the discussion of the MS.

In addition, the authors conducted a toxicity study with only one plant, which is not sufficient to draw the correct conclusions, in my opinion.

I have also found it problematic that the authors do not give information about the arsenic forms in the tested environmental elements. Although the toxicity of arsenic highly depends on its form. Besides, the mobility of arsenic compounds in soils depends on the type and amount of adsorbing soil constituents, the pH value, and the redox potential etc.

I have a few comments or suggestions which may indicate points for further improvement. Please see the specific comments below.

Specific comments

“Abstract” is well written and reflects clearly the actual scope of this manuscript.

“Introduction”

There are more than 50 references listed in the MS, but some important aspects connected to this topic are missing, as I mentioned in “General Comments”. In my opinion, the “Introduction” needs major revision. This part of the article is practically just about dam management topics. Besides, the reclamation possibilities of mine abandoned areas are summarized in a short section, but unfortunately it is incomplete.

Please see:

Paulo J.C. Favas, Louis E. Martino, Majeti N.V. Prasad, (2018) Chapter 1 - Abandoned Mine Land Reclamation—Challenges and Opportunities (Holistic Approach), Editor(s): Majeti Narasimha Vara Prasad, Paulo Jorge de Campos Favas, Subodh Kumar Maiti: Bio-Geotechnologies for Mine Site Rehabilitation, Elsevier, 2018, Pages 3-31, ISBN 9780128129869,

It would be more important to give more attention for example to arsenic chemistry, bioavailability as well as factors influencing its mobility.

In addition, it would be good to formulate objectives at the end of this section in line with the conclusions. Line 71-74: Please rewrite this section.

 

“Materials and Methods”

Line 81, 84: Please define exactly “top soil”. The sampling was carried out in September 2019. Are there available previous results/data about the contamination at the site? Line 101: Please delete “weight”. Line 113: Please correct: “water samples”. The applied chemical methods and techniques employed are appropriate. Please give explanation (more detailed description) about different fractions (f1, fr2 and fr5) in connection with arsenic forms. Section 2.4: Why was only one plant species applied for biological assessment? Please give explanation. The statistical analysis is correct. Please check this part for appropriate professional language use.

 

“Result and Discussion”

Figures and Tables are usually informative, easily readable and correct. But please give SD values to the Table 1 and Figure 3. Please give a more detailed comparative discussion between soil properties and arsenic forms. Arsenic is a redox sensitive element which can exist in multiple oxidation states. The environmental fate, bioavailability and toxicity of arsenic vary dramatically with its chemical forms. Section 3.4: In my opinion, correlation analysis should be performed to study the relationship between soil properties, the results of chemical assessments and phytotoxicity test.

“Conclusion” part is well-written and it is supported by the obtained results. The future R&D directions are also defined.

“References”

Only a few of the literature cited deal with factors affecting arsenic mobility and phytotoxicity, which is the main topic of this MS. The ”doi” is missing from most references provided.

The manuscript needs to be checked for appropriate professional language usage and for grammar and syntax. Grammatical editing of the paper is strongly recommended.

Finally, in my opinion the manuscript needs major revision.

Author Response

At first, thank you for your review.

 

Line 45. Favas's reference was added for dam information.

Line 73-75. The objective of this study was edited.

Line 81. top soil was defined. We also tried to look for historical data in many ways, but unfortunately it was difficult to find data that could be accessed as a university researcher.

Line 127. Deleted 'weight'

Line 88. Edited 'water samples' 

Section 2.4. 

Our team has been conducting phytotoxicity tests on leafy vegetables for a long period of time and believes that we have a fairly high level of experimental expertise and reproducibility. Among the various plants, bok choy was selected because past heavy metal soil studies have shown that the plant species is neither too sensitive nor too dull for toxicity and can be compared with past data. Also, this is because it is expected to be used as an important research resource by continuously accumulating toxic results on the target plant species and establishing a database. In addition, it is practically difficult to test several species at the same time on the soil, which we deal with at first time.

Figure 3 and Table 1. 

For readers, we didn't add SD to improve table readability. In particular, the number of digits in Table was also varied, so the table looked very messy with SD. In the case of Figure 3, it is difficult to express SD on the figure because the distribution of the percentage of arsenic in the R and F soils is clearly visible at a glance. Fr1, Fr2, Fr3, Fr4r, and Fr5 can be represented as independent bar graphs, but important messages were not likely to be delivered.

Redox conditition.

Compared with cationic heavy metals, As has been known to have a significant effect on redox condition in mobility, effectiveness, and toxicity. If this study was conducted on flooded soils (like paddy soil), experiments and considerations would have been carried out. However, since As in forest soils in oxidized state was dealt with, it could not be covered. As speciation of sediments is currently under examination for further study.

Section 3.4

As the reviewer said, phytotoxicity data were used for statistical analysis in many ways, but some of the data was so popping (for example R2 and R6) that makes it difficult to understand but produces statistically significant results. So it could not produce acceptable results in general and was not added in the manuscript.

References

We added DOI.

 

Thank you again.

 

 

Reviewer 3 Report

Assessment of arsenic mobility and potential bioavailability are important in order to predict environmental hazardousness of the specific example of pollution.   

Please check spelling and grammar (line 79, Table 1, line 192, line 259)

Figure 1. Sampling points for soil F and water and sediments samples  are not readable  from the figure.  

Please give reference to the standard methods for sediment analysis (lines 113-115).

Do  references  25 and 26 deal with arsenic? How can they be considered to decide about mobile fractions of As (line 123)?

The reason of selection of single extraction methods is not sufficiently justified (selection of SBET procedure ?).

The results about f3 fractions differ greatly between soil R and soil F samples.  Have the authors tried to find out the specific metal oxides present in soil R or soil F samples?

Why did not authors calculate extracted As concentrations by single extraction as presentage of total concentration for different samples?   

I would recommend to use the term bioavailabilty throughout the text (instead of bioaccessibility in lines 261, 262, etc. ).

The phytotoxicity of some samples could be caused by low pH as authors also mention in the paragraph 3.4. There is not possible to correlate the inhibition of root or shoot growth with neither high total content nor high bioavailability of As in samples.

May-be the authors consider to  write about of meaning of the  determined fractions  instead of  using  abbreviations  f1, f2, f3  in the Conclusions.  

Author Response

Line 79, 192, 259. We checked it.

Figure 1. We edited it more readable.

Standard methods for sediment analysis. - This method was written in Korean word and published by NIER (National Institute of Environmental Research).

Reference 26, 27. Both references deal with cationic heavy metals. But looking at the principle of dissolution by leaching solution, the explanation of each step is similar. And although not included in the manuscript, there are also literatures that use arsenic sequential extraction steps. e.g. Sofianska and Michailidis, 2015 (Chemical assessment and fractionation of some heavy metals and As in agriculutral soils of the mining affected drama plain, macedonia, northern greece) 

SBET test was selected for assessment of human health risk in order to simulate the exposure pathway through wind inhalation of nearby residents. The area under study is located in a mountain valley, where wind-borne contaminant soil particles can easily migrate.

Specific metal oxides:

This is the first research site we have encountered, and it is the place where no intensive research has been conducted in Korea as in this paper. In this way, the primary screening was completed through this study. In the spring of 2020, the soil samples are collected in a wider range, and the XRD analysis of the co-author's research institute is planned. Forensic research is also expected through pollutant tracking through XRD analysis.

Single extraction

We processed it to represent the data in various ways. Overall, the total content is very high, so some leaching methods do not show much contact with the percentages, so they are avoided.

Bioaccessibility: We changed it.

Phytotoxicity test result: As the reviewer noted, we are designing an experiment to see the plant's response to changes in pH and effectiveness through amendment treatment to interpret the trend for this result.

Conclusion: we edited

 

Thank you again!

Round 2

Reviewer 1 Report

The document was well improved and the changes were justified. Accepting the paper in its current form. 

Reviewer 2 Report

Dear Editors, Dear Authors,

Concerning the revised MS (Sustainability-692085, “Assessment of fraction and mobility of arsenic in soil near the mine waste dam”.) it can be seen that major revisions have been done. Authors have taken note of the most comments provided. They also added explanations to the issues raised in their response. The corrected paper is enriched by new or modified parts, explanations and relevant references.

Finally, in my opinion the MS is acceptable for publication after minor spell check.