Are Ecological Risk Indices for Trace Metals Relevant for Characterizing Polluted Substrates in the Katangese Copperbelt (DR Congo) and for Assessment of the Performance of Remediation Trials?
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsDetailed comments:
· The authors included too many topics in the manuscript, and none of them were fully developed.
· The keywords do not reflect the content, some are even misleading.
· High concentrations of heavy metals in the soil do not necessarily mean a high level of bio-accessibility of these metals. Bioconcentration factor values below 1, indicate not only low accumulation in roots, wood, and leaves but also a low level of bioaccessibility of these metals in the soil environment.
· Why the pseudo-total heavy metal content in soil samples was determined by the aqua regia digestion whereas in leaf and root samples by the HNO3/HClO4 digestion.
· For what purpose was the extractable fraction of heavy metals in the soil determined (by extraction with CH3COONH4 and EDTA solution)? Where are these results?
· According to the reviewer, the mere statement: "it seems that the pollution indices used are unsuitable for assessing the effectiveness of phytotechnology processes based on metal stabilization" is insufficient. Geochemical fractions of heavy metals should be determined. The appropriate tool is chemical fractionation.
· Conclusions require rethinking.
Author Response
Dear reviewer,
We would like to thank you for taking the time to carefully review our article and provide constructive feedback and suggestions.
Please find attached the replies to your comments.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for AuthorsComments and Suggestions for Authors
The present study Are indexes of ecological risk associated with trace metals relevant for the characterization of mine tailings and polluted soils in the Katangese Copperbelt (DR Congo) and for assessment of the performance of remediation trials deals with the assessment of ecological risk posed by heavy metals in soil as a result of mining industrial activities.
In general, the manuscript is interesting and suitable for publication in the Environments journal. However, I have noted some grey points in the current version which need to be corrected in a major revision.
My specific comments are:
1. I recommend the authors to improve in the title, it is unclear. The title is an interrogative?
2. The objective of the work is not clearly outlined in the introduction section.
3. It is not clear what is the novelty of the study? The study is actually a synthesis of several experimental studies.
4. Why there are no assessments of soil physico-chemical parameters like redox potential, electrical conductivity, organic carbon etc. ? These are the most important factors controlling soil elemental dynamics. Please provide.
5. Physical structures such as particle size and moisture content should be given and discussed, because these are the factors which influence elemental sources, or parent rocks.
6. The part of experimental methods should be described more rigorously. How was the biomass and wood digested, under what experimental conditions?
7. Table 4. - Do the data describe the CF of metals in soils or wastes? Please avoid such ambiguity.
8. Why has been chosen to analyze only Co, Cu, and Zn in plants? What is the explanation why the concentration of metals is very low in the wood? Also, the BCF is lower than 1, these data must be discussed in terms of the bioavailability and mobility of metal species and translocation mechanism and not as concentration values. The results must be discussed from the perspective of the mechanism involved in the process. Line 356-360 – please, mention de unit for metals concentration.
9. Line 80-82 – “the metal pollution indices …… could also be a relevant tool to assess the metal concentrations themselves.” Can the authors explain what they intended to say, because the risk indices are calculated based on the concentrations determined in the soil?
10. Line 153 - Leucena leucocephala correct Leucaena leucocephala;
11. Line 192-197 Table 2 Classification of enrichment factor, see: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7652249/
12. Line 215 - ecological factor (Er) it is about Ecological risk factor.
13. Table 2 - Toxological response factor change with toxicological or Toxic response factor.
14. Line 371 - What do the authors mean by "secondary metallic habitats"?
15. Line 375- mineralogical composition, please check!
16. Line 396-397 - From this perspective, it would be interesting to discuss the risks to human health generated by the presence of these metalloids in the soil and the solutions that are advocated for the reduction of human health and ecological risks.
17. Line 477 – 479 - Considering the initial HM concentration in soil, it is well known that phytoremediation can be a viable solution for low concertation of toxic compounds and by applying phytoaccumulation plants.
18. Section 4.3 – The discussions are ambiguous and unargued. Ecological risk assessment is a tool used in decision-making, the results provided by these kind of studies may conduct to a set of remediation alternatives.
19. The analysis of data from the perspective of national or international standards regarding the concentrations of heavy metals and metalloids contained in soils could bring a reference element in support of the objectives of the work.
20. I may suggest the authors to analyze the situation from the perspective of PLI- Pollution Load Index and PERI—Potential Ecological Risk Index.
22. Some references are very old, I recommend to replace them with some references from the last 5 years.
Comments for author File: 
Comments.pdf
Some of the paragraphs do not make sense or have mistakes in expression, for a good understanding of the content I suggest revising the English language.
Author Response
Dear reviewer,
We would like to thank you for taking the time to carefully review our article and provide constructive feedback and suggestions.
the answers to your comments are in the attached file
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsI agree with the publication of the manuscript in this form.
Comments for author File: Comments.pdf
