Spatial Heterogeneity of Rare Earth Elements: Implications for the Topsoil of Regional Ion-Adsorption Type Rare Earth Deposit Areas in Southern China
Round 1
Reviewer 1 Report
The abstract should be shortened somewhat and the results should be summarized.
The introduction should describe in more detail how ion adsorption type deposits REE are formed and how REE migrates in the soil during physical and chemical weathering. Part of the introduction on Ln80-100 belongs more to the part of discussion and comparison with literature values.
At the end of the introduction, the objectives and purpose of the research are missing.
What does it mean that you took samples from profiles?
You took 65 samples from 18 profiles? Or samples along profiles? If letter, to what depth and at what distance? Please correct/reword.
It is not clear how the samples were digested and what served as quality control?
The numbers in the tables and text should be reduced to three significant figures. Everything else is unnecessary. For example: 0.23; 2.34; 45.6 or 102.
The Tukey test should be mentioned in Materials and Methods.
Not all samples are shown in Figure 2, only the selected samples and the reason for this selection should be indicated.
The manuscript is very difficult to understand. It seems like a bunch of data was just thrown into the paper without any deeper discussion and somehow it is not at all clear what the authors wanted to achieve with this manuscript.
Please revise the language and structure of the manuscript. I think it contains useful information, but in this form it is not suitable for publication.
Perhaps it would not be a bad idea to shorten the manuscript a bit or at least divide it into subsections and clarify the purpose of what was done at the beginning of each subsection and then end that subsection with a semi-conclusion.
The conclusion should be reworded as it should not repeat what has already been said, but should present the concluding thoughts in a concise and clear manner.
English needs to be revised.
Author Response
Dear Editor and Reviewer,
Based on your feedback and suggestions, the author has carefully revised the manuscript one by one to address any issues. The revised version marked in the revised manuscript. Please review it.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The migration and spatial distribution characteristics of topsoil rare earth elements are significant for the risk assessment of external environment. However, the spatial distribution of REEs in the topsoil of ion-adsorption type rare earth element mining areas is poorly studied.
The Abstract covers all the important issues this article is dealing with. The authors gave the overview concisely.
The introduction addresses previous results on REEs in the topsoil. Due to the fact that the ore-forming parent rock of the ion type rare earth ore in the research area is granite, which forms a thick weathered crust residual layer after weathering, in which rare earth ions are enriched. Whether ion type rare earth minerals can be formed is related to the ore-forming parent rock, topography, and climate environment. The key factors are the lithology and chemical weathering rate of the ore-forming parent rock, providing conditions for the formation of weathering crust in the later stage. The distribution of rare earth elements in the surface soil layer studied in the article is a part of the early formed weathering crust, and the geological environment of the surface soil layer is closely related to human production and life. Therefore, on the basis of sustainable development of ionic rare earth mining, this article focuses on protecting the soil environmental quality of the topsoil layer.
Sampling methods are explained in details.
The "implications" section is focusing on explaining the reasons for the enrichment of rare earth elements in the topsoil layer.
The Conclusion is clear about the controlling factors that reflect the spatial distribution pattern of rare earth enrichment in the surface soil layer.
Author Response
Dear Editor and Reviewer,
Based on your feedback and suggestions, the author has carefully revised the manuscript one by one to address any issues. The revised version marked in the revised manuscript. Please review it.
Question 1: The migration and spatial distribution characteristics of topsoil rare earth elements are significant for the risk assessment of external environment. However, the spatial distribution of REEs in the topsoil of ion-adsorption type rare earth element mining areas is poorly studied.
Answer 1: At present, the focus of attention on the soil environment of ion type rare earth mines at home and abroad is mostly on the tailings of early rare earth mines and soil pollution after in-situ leaching. However, there is relatively little research on the content, spatial distribution, and migration characteristics of rare earth elements in the surface soil layer of southern rare earth mining areas. This makes it difficult to implement the standards used for soil environmental quality management of rare earth mines, and poses risks such as reduced effectiveness in soil environmental management. Based on the above objectives, this article discusses in detail the spatial distribution and heterogeneity of rare earth elements in the topsoil layer, and predicts the spatial distribution of rare earth elements in the region through analysis of surface soil sample sampling and profile sampling. This provides a reference basis for soil environmental management in the region.
Question 2: The Abstract covers all the important issues this article is dealing with. The authors gave the overview concisely
Answer 2: The author carefully revised the abstract based on the comments of the reviewers, removing unnecessary descriptive sentences to make the abstract more concise. See revised version.
Question 3: Sampling methods are explained in details.
Answer 3: According to the reviewer's comments, the author has added a description of the profile sampling and listed the sampling depths. Further improved the sampling method. See revised version.
Question 4: The "implications" section is focusing on explaining the reasons for the enrichment of rare earth elements in the topsoil layer.
Answer 4: The main objective of this section is to explain the differentiation patterns and enrichment factors of rare earth elements in the topsoil layer, and to supplement the previous discussion section.
Question 5: The Conclusion is clear about the controlling factors that reflect the spatial distribution pattern of rare earth enrichment in the surface soil layer.
Answer 5: Based on the reviewer's comments, the author further revised the conclusion to make it clearer and more readable. See revised version.
Reviewer 3 Report
This paper analyzed the spatial heterogeneity of REEs in the topsoil of Jiangxi Province, China that is the region with abundant ion-adsorption REE deposit. Though this paper has provided a great amount of data, the discussion section is superficial and did not provide new insight. Thus, the current edition could not by accepted for publication. I provide some suggestions as follows:
1. Though the introduction section has provided a lot of information, the thesis and scientific question have not been well illustrated. For example, why did the authors focused on the spatial heterogeneity of REEs in the topsoil of regional ion-adsorption REE deposits.
2. Line 229: Why did the patterns was normalized by chondrite, but not North American shale?
3. This study focuses on the spatial heterogeneity of REEs on the topsoil. Why did the authors report the vertical distribution of REEs in soil profiles, which I think it is not relevant and did not provided any novel insights?
4. The results are compared to the previous study on Baotou and Sichuan basin topsoil. But in fact, they are different types of REE deposit.
5. The discussion section is superficial and did not provide new insight. I suggest the authors add more evidence.
English Language is good.
Author Response
Dear Editor and Reviewer,
Based on your feedback and suggestions, the author has carefully revised the manuscript one by one to address any issues. The revised version marked in the revised manuscript. Please review it.
Question 1: Though the introduction section has provided a lot of information, the thesis and scientific question have not been well illustrated. For example, why did the authors focused on the spatial heterogeneity of REEs in the topsoil of regional ion-adsorption REE deposits.
Answer 1:
In the introduction, the author added the problem and necessity of studying the spatial heterogeneity of REEs in the topsoil, highlighting the writing goal of this paper. See revised version
Question 2: Line 229: Why did the patterns was normalized by chondrite, but not North American shale?
Answer 2:
At present, there is no unified method for standardizing rare earth chondrites. When the author chose the standardization method for rare earth elements in the topsoil layer, the main consideration was the consistency with the standardization of the ore-forming parent rock, that is, the reference [32] CI chondrite standardization method was used for processing, so the "North American shale composite" standardization method was not used.
In addition, through detailed comparison, the author found that the chondrite value given by "North American shale composite" is relatively small, which indicates that The δEu, δCe index discrimination has an important impact, so the author chose to use the CI chondrite standardization method. Is this method appropriate? Please review and provide valuable feedback.
Question 3: This study focuses on the spatial heterogeneity of REEs on the topsoil. Why did the authors report the vertical distribution of REEs in soil profiles, which I think it is not relevant and did not provided any novel insights?
Answer 3:
The review teacher's viewpoint has important reference value.
After discussion, the author believes that this paper studies the distribution and spatial heterogeneity of REEs in the topsoil. Conceptually, its spatial distribution characteristics should be 3D manifestations, such as the distribution characteristics of REEs in the 20cm topsoil, 60cm, 100cm and 120cm downward, etc. How are the distribution characteristics of rare earth elements in different depth layers distributed? Unfortunately, due to objective conditions, this paper has not been able to study more profiles to reveal the changes in REE content at different depths, nor can it reveal the spatial heterogeneity of REE at different depths. The main reason is that the number of profile studies is too small.
In addition, the author used three profiles to explain the differences in the distribution of LREE and HREE in the topsoil layer δEu, δCe, this difference in vertical variation is the result of rare earth element migration, providing a basis for analyzing the spatial differentiation of rare earth elements in the topsoil layer.
Perhaps the author's understanding is not deep and comprehensive enough, please review the teacher and provide valuable suggestions.
Question 4: The results are compared to the previous study on Baotou and Sichuan basin topsoil. But in fact, they are different types of REE deposit.
Answer 4:
This article compares the rare earth element content in the surrounding soil (topsoil) of Baotou rare earth mine, Sichuan Basin (Jiangjin) topsoil, Qinghai Tibet Plateau and other topsoil, with the main purpose of explaining that there are significant differences in REE fractionation in the weathered crust and soil formed by weathering of different rocks. The Baotou rare earth mine belongs to a light rare earth enriched mining area, so the content of LREEs in the topsoil is higher than that in the study area; The fractionation of REEs in the surface soil layer of the Sichuan Basin is influenced by factors such as topography, pH value, and soil organic matter. The above large tectonic environment has significant differences from the research area, which is reflected in the significant differences in REE content in the topsoil.
When conducting literature research, the author was unable to retrieve relevant literature on the content of rare earth elements in the surface soil layers of southern China, while reference [23] provided important information on the content of rare earth elements in the surface soil layers for this article.
Therefore, the author reveals that the fractionation of rare earth elements in the topsoil of the study area is closely related to the geochemical behavior of rare earth elements.
Question 5: The discussion section is superficial and did not provide new insight. I suggest the authors add more evidence.
Answer 5:
Based on the reviewers' opinions, the author attempted to conduct a rare earth risk assessment in the discussion section, supplemented the literature, and proofread the references and conclusions in the entire text. The supplementary content is as follows:
The cancer slope factor (SF) is used to assess the risk of carcinogenesis as follows [44]
Riski = EDIs×SFi （3）
RiskTotal = (4)
Among them, Riski is the carcinogenic health risk of the ith rare earth element; EDIs is estimated daily intake (μg·kg-1·d-1) of bioaccessible REEs via leafy vegetables, root vegetables and drinking water consumptions for local people of different gender/age groupï¼»23ï¼½, the average value 55.4kg·μg-1·d-1 is used in this article. RiskTotal is the sum of the Riski values of all REEs. According to the US EPA Integrated Risk Information System (IRIS) ï¼»45ï¼½, the cancer slope factor SF was shown in Table 5:
Table 5.
Risk assessment of rare earth elements in the topsoil
|
REE |
SF (kg·day-1·μg-1)ï¼»45ï¼½ |
Mean of CI chondrite standardization （μg·kg-1） |
Riski |
Concentrations of ion-exchangeable REEs（μg·kg-1）［23ï¼½ |
|
La |
1.10×10-8 |
1.24×10-4 |
6.09×10-7 |
2.44×10-5 |
|
Ce |
3.52×10-8 |
9.90×10-5 |
1.95×10-6 |
3.58×10-5 |
|
Pr |
7.92×10-9 |
1.16×10-4 |
4.39×10-7 |
6.65×10-6 |
|
Nd |
5.44×10-10 |
1.11×10-4 |
3.01×10-8 |
2.61×10-5 |
|
Sm |
3.74×10-8 |
1.98×10-4 |
2.07×10-6 |
4.69×10-6 |
|
Eu |
1.03×10-8 |
9.07×10-6 |
5.71×10-7 |
6.82×10-7 |
|
Gd |
1.52×10-9 |
2.15×10-4 |
8.42×10-8 |
3.92×10-6 |
|
Tb |
4.88×10-9 |
2.24×10-4 |
2.70×10-7 |
5.65×10-7 |
|
Dy |
4.14×10-10 |
2.18×10-4 |
2.29×10-8 |
2.88×10-6 |
|
Ho |
9.21×10-9 |
2.13×10-4 |
5.10×10-7 |
5.27×10-7 |
|
Er |
2.53×10-9 |
2.20×10-4 |
1.40×10-7 |
1.43×10-6 |
|
Tm |
6.99×10-10 |
2.37×10-4 |
3.87×10-8 |
1.89×10-7 |
|
Yb |
4.00×10-9 |
2.32×10-4 |
2.21×10-7 |
1.07×10-6 |
|
Lu |
3.53×10-9 |
2.47×10-4 |
1.96×10-7 |
1.53×10-7 |
The carcinogenic risk of Riski or RiskTotal is classified as: No Significant risk(<10-6); acceptable/tolerable (10-6~10-4); unacceptable (>10-4) [46].
From Table 5, the risk of rare earth intake in the topsoil of the study area was not significant, and Ce and Sm were within an acceptable range. Comparing the rare earth ion exchange concentration in the weathered crust around Guangzhou, the highest conversion rate of dissolved rare earth ions in the soil was reached 108% [23]; The average content of rare earth elements in the topsoil layer of this area was ranged from 10-4 to 10-6, and their exchange and transformation were caused significant environmental risks over time.
Round 2
Reviewer 1 Report
The authors have accepted all comments and corrected the manuscript accordingly. I think it is now of sufficient quality to be published. I only ask that in the proofing phase all extra decimal places are removed from numbers above 99.999 (e.g. 104.7 or 1054.2 makes no sense, it should be written 105 and 1054).
Reviewer 3 Report
The current edition can be accepted now.
