Review Reports

Round 1

Reviewer 1 Report

Comments to the Article “Assessment of Soil Pollution with Presumably Contaminating Elements in Moscow Using Neutron Activation Analysis”, by Inga Zinicovscaia et al.

The authors in this paper focus on assessing soil pollution with PCEs, to increase the level of information about the geochemistry of top soil, and to search for (dis)similarities in the first two layers of top soil in order to quantify the contamination degree.

The Introduction section properly presents the problem, and the Materials and Methods section is illustrative. The Results and Discussion section is well organized

The references in the text are up to date.

The authors should address revisions.

    - An extensive editing of English language is mandatory. For example, at line 44, “…contamination, allows permits to identify…”; at line 106, “… 1 min at at a thermal…”

·       - The range of possible values for I_geo regarding an unpolluted to moderately polluted soil, at line 143, is not well represented.

·       - At line 178, the correlation coefficient is named Spearman, not Spearmint.

·       - At line 196, “were” or “where”?

·       - At lines 229 and 230, words “a similar situation” are repeated.

·       - The caption of Table 3 mentions the distribution of 28 trace elements, while the caption of Figure 3 mentions 29 trace elements. How many are they?

·       - A reference is missing at line 250.

·       - Words repeated in line 266.

·       - What is the meaning of the sentence in lines 289 and 290?

·    - The Conclusions section is poor. Any perspectives for future work? Any interest in applying geostatistics to analyze the spread of pollutants?

Author Response

Dear Reviewer,

Thank you for the time you have spent as well as for the quality of your remakes and advices

Here are my our answers (correction in red ink)

Comments to the Article “Assessment of Soil Pollution with Presumably Contaminating Elements in Moscow Using Neutron Activation Analysis”, by Inga Zinicovscaia et al.

The authors in this paper focus on assessing soil pollution with PCEs, to increase the level of information about the geochemistry of topsoil, and to search for (dis)similarities in the first two layers of topsoil in order to quantify the contamination degree.

The Introduction section properly presents the problem, and the Materials and Methods section is illustrative. The Results and Discussion section is well organized

The references in the text are up to date.

The authors should address revisions.

Remark: An extensive editing of English language is mandatory. For example, at line 44, “… contamination, allows permits to identify…”; at line 106, “… 1 min at at a thermal…”

Answer: we have corrected (red ink)

Remark: The range of possible values for I_geo regarding an unpolluted to moderately polluted soil, at line 143, is not well represented.

Answer: we have corrected by including log­₂ in the equation 3. Accordingly, Igeo takes also negative values

Remark: At line 178, the correlation coefficient is named Spearman, not Spearmint.

Answer: we have corrected

Remark: At line 196, “were” or “where”?

Answer; we have corrected

Remark: At lines 229 and 230, words “a similar situation” are repeated.

Answer: we have corrected

Remark: The caption of Table 3 mentions the distribution of 28 trace elements, while the caption of Figure 3 mentions 29 trace elements. How many are they?

Answer: We have corrected – 28 elements

Remark: A reference is missing at line 250.

Answer: we have corrected Ref. 31

Remark: Words repeated in line 266.

Answer: we have corrected

Remark: What is the meaning of the sentence in lines 289 and 290?

Answer: The sentence was removed

Remark: The Conclusions section is poor. Any perspectives for future work? Any interest in applying geostatistics to analyse the spread of pollutants?

Answer: We have changed accordingly. We have also mentioned that our study covers only a small part of the Moscow municipality. For this reason we have not used any ArcGis maps as the sampling point density was to small for such large territory.

Reviewer 2 Report

It is overall a well-written paper, so its publication is recommended.

There is one typo in Figure 4a: recicling-> recycling

Please double-check that the high uncertainty range for Ca in Figure 4b is realistic.

In the case of NAA, the methodology for flux determination and concentration calculation shall be added. Is it a relative method using the listed CRMs? Then they are not only for quality control but part of the calculation procedure. Please add a short explanation to section 2.2.

Author Response

Dear Reviewer,

Thank you for the time you have spent as well as for the quality of your remakes and advices

Here are my our answers (correction in olive ink)

It is overall a well-written paper, so its publication is recommended.

Remark: There is one typo in Figure 4a: recicling-> recycling

Answer: we have corrected

Remark:Please double-check that the high uncertainty range for Ca in Figure 4b is realistic.

Answer: We have checket it. The great uncertainty range is due to great variability of the Ca mass fraction of which values, as CaO, varied between 3.15 and 21.52 %wt (Table 1SM- Suplementary Material)

Remark: In the case of NAA, the methodology for flux determination and concentration calculation shall be added. Is it a relative method using the listed CRMs? Then they are not only for quality control but part of the calculation procedure. Please add a short explanation to section 2.2.

Answer: We have explained (Rows 110-113) : For all INAA measurements we have used a relative method to determine the mass fractions of all 37 elements, excepting Hg was used. To attain a higher confidence level, we have used more Certified Reference Materials, some of them for the Quality Control too were applied (Table 2SM - Supplementary Material).

Reviewer 3 Report

General Comments:

 This study shows an interesting exploratory assessment of soil contamination in urban and peri-urban soils by different elements after applying different geochemical index.

These are the main weaknesses of the study:

1.- the number of soil sampling points, only 15 for an area (estimated from the scale in figure 1) about 2000 km2 is excessively low to obtain a representative view of the pollution level across the study area. Therefore, authors must explain the representativeness of its soil sampling protocol.

2.- Quality control of analytical determinations is far from be clear, as no information was provided about the certified values of standard material used.

3.- The use of element values in UCC for EF, CF and Igeo calculation is not adequate. There is a vast body of literature showing criticism with this approach due to the extremely high variability in the concentrations of most of chemical elements across the Upper Continental Crust. The use of element concentrations in more local samples (a deeper soil layer or a sample of the local lithology in each sampling point) is considered much more proper.

4.- The discussion is mostly focused on tracing the geochemical nature of the soil composition instead to look for a relationship between the results of the ecological indices and the potential contribution of anthropogenic point sources of contaminants to their surrounding urban soils.

 

I am not a native English speaker but, in my knowledge, it would be necessary a language editing (this must be provided, free of charge, by the own editorial).

 In the basis of the previous comments (besides to specific comments described underneath), I consider that the manuscript needs a substantial improvement before acceptation.

 Specific Comments:

 Abstract:

 Some results are needed in the abstract (as example, some noticeable values of EF or for Igeo…)

Introduction:

The first part of the introduction (lines 14-48) should be reduced, and a background about ecological risk indices application in previous studies on PCEs pollution in urban soils must appear.

The aims of the study should be refined.

 Material and Methods:

 Lines 95-100. What is the distance between soil sampling point and the corresponding TPP, WIP or MPP? Perhaps, it would be useful include this information in table 1. What were the reason for such soil sampling depths? Information about this must appear in the text. What do you mean with “cleaned”? Were soil replicates mixed in a unique composite soil sample for each sampling site and depth? Please, much more details about soil collection and preparation should be add in the text or, if it applicable, as supplementary material.

 Lines 113-121. Authors must include, as supplementary material, the certified values for all analysed elements present in the standard reference materials used. Where do all PCEs analysed in soils samples certified in any of the SRM? Considering the high thermal lability of Hg, did you check if Hg could be lost after drying at 105ºC?

 Lines 154-162. The use of parametric statistical test could be not adequate if requirement about normal distribution and homogeneity of variance were not satisfied. More detail explanations about what test, and in what context, were they used. Otherwise, the robustness of the statistical results could be put in question.

 Results and Discussion

 Line 166. What do you mean with “soil basic material”? This is not a term usually used in studies on soil pollution. Please, add some explanation.

 Line 171-173. Considering the abovementioned comment regarding the usefulness of UCC for EF, CF and Igeo values, a similar criticism can be applied to these results. Table 1SM was not found in the submitted manuscript. (Neither Table 2SM, Table 3SM and Table 4SM).

 Lines 175-178. “Spearmint´s”? Please, check. What is the true finding suggested in line 179? Please, authors must be much more explicit. If they want to say that there is no difference in major element concentrations between 0-5 and 5-20 soils layers, them let´s say something like this. In what extent that normalization of mass fraction of major elements to the UCC contents could hint differences between soil layers? Did you check such differences with non-normalized mass contents?

 Regarding Figure 2, what about fig 2e? Why figure 2 goes from 2d to 2f?

 Lines 218-220. Please, check this range of contents for trace elements. In addition, organic matter also plays a key role in the accumulation of trace elements in soils, especially in the uppermost soil layers where more organic matter is usually accumulated. What about the role of soil organic matter in the mass fraction and ecological risk indices for trace elements?

 Line 229. There is a typo in this line.

 Regarding Figure 3, the position of some trace elements cannot be distinguished in figure 3a. What is the blue shadowed area in figure 3a? Please, remember that figure must be auto-explicative. In these graphics appear a lot of details which are not explained in the figure caption (error bars?, what are the continuous (3a) and dashed (3b) lines?, what do mean the dashed ellipses in 3d? and so on…

 Line 240. Dou you mean fig 3c when you refer to Th/Co vs La/Sc? Please, check.

 Lines 257-262. The hypothesis that authors try to explain must be much more explained. It is quite difficult to extract from figure 4b what the really want to mean.

 Lines 280-300. It is extremely difficult to follow the reasoning of the authors for several reasons. First, no allusion to true results (values) of EF appear in the text (see as example lines 293-294 when authors talk about EF of Hg). Second, authors talk about EF of elements from which reader have not values in the text or in figures. Third, it is quite difficult to follow what is showed in figures when soil samples in figures and soil samples in the text have different names (from 1 to 15 in figures and names remember anthropogenic point sources such as WIP Nº or TPP Nº are used in the text). Perhaps unifying the nomenclature of soil samples would favour the understand.

 Lines 307-308. I think that, in addition to vehicles, other anthropogenic sources could account in a better extent for the moderate pollution of Hg. The emissions from thermal power plants or waste incinerators are more likely to contribute in a greater extent than vehicles to Hg pollution in the studied soils. I think that, at least, these other sources should be also take into account to explain such moderate values of Igeo for Hg in some soils.

 Lines 311-323. There is no discussion about CF values as these lines only represent a somewhat confusing description of results for this ecological risk index.

 Conclusions:

 Conclusions should be rewrite according to the necessary improvements in the text.

 

Author Response

Dear Reviewer,

Thank you for the time you have spent as well as for the quality of your remakes and advices

Here are my our answers (correction in purple ink)

This study shows an interesting exploratory assessment of soil contamination in urban and peri-urban soils by different elements after applying different geochemical index.

These are the main weaknesses of the study:

Remark: 1.- the number of soil sampling points, only 15 for an area (estimated from the scale in Figure 1) about 2000 km² is excessively low to obtain a representative view of the pollution level across the study area. Therefore, authors must explain the representativeness of its soil sampling protocol.

Answer: It is absolutely true, but our project concerned only those recreational areas situated in the vicinity of great contamination enterprises. For this reason, we could not got maps depicting the PCE distribution all over the territory. We have mentioned this fact in the “Conclusions”.

Remark 2.- Quality control of analytical determinations is far from be clear, as no information was provided about the certified values of standard material used.

Answer: We have provided a complete list of Certified Reference Materials (CRM)used as well as of the results of our determinations usin thes ame CRMs (Table 2SM – Supplementary Material)

Remark 3.- The use of element values in UCC for EF, CF and Igeo calculation is not adequate. There is a vast body of literature showing criticism with this approach due to the extremely high variability in the concentrations of most of chemical elements across the Upper Continental Crust. The use of element concentrations in more local samples (a deeper soil layer or a sample of the local lithology in each sampling point) is considered much more proper.

Answer: We totally agree that the UCC represents rather a concept, which does not take into account the local geochemistry, but in the absence of some unanimously accepted limits for soil contamination with Presumably Contaminating Elements (PCE), we have considered the UCC as the most conservative approach and we have mentioned it (Rows 160-163).

Remark 4.- The discussion is mostly focused on tracing the geochemical nature of the soil composition instead to look for a relationship between the results of the ecological indices and the potential contribution of anthropogenic point sources of contaminants to their surrounding urban soils.

  Answer:

I am not a native English speaker but, in my knowledge, it would be necessary a language editing (this must be provided, free of charge, by the own editorial).

  In the basis of the previous comments (besides to specific comments described underneath), I consider that the manuscript needs a substantial improvement before acceptation.

 Specific Comments:

 Abstract:

Remark: Some results are needed in the abstract (as example, some noticeable values of EF or for Igeo…)

Answer: we have changed the Abstract accordingly

Introduction:

Remark: The first part of the introduction (lines 14-48) should be reduced, and a background about ecological risk indices application in previous studies on PCEs pollution in urban soils must appear. The aims of the study should be refined.

Answer: WE have removesd only some fragments, by keeping the majority of Introduction content as the number of paper devoted to a simultaneous analysis of soil geochemistry and teis degree of contamination is very reduced. We considered that for a potential reader, any detailed information on these subject may be welcome.

 Material and Methods:

  Remark: Lines 95-100. What is the distance between soil sampling point and the corresponding TPP, WIP or MPP? Perhaps, it would be useful include this information in table 1. What were the reason for such soil sampling depths? Information about this must appear in the text. What do you mean with “cleaned”? Were soil replicates mixed in a unique composite soil sample for each sampling site and depth? Please, much more details about soil collection and preparation should be add in the text or, if it applicable, as supplementary material.

Answer: Thank you for your comment! The main scope of the present study was to assess the possible effect of thermal power plants and waste incineration plants on soil pollution in Moscow recreational areas. Therefore, samples were collected only in the vicinity of thes objects. It was not the aim of the study to assess the level of soil pollution in the whole Moscow.

Answer: The distances between soil sampling point and the corresponding TPP, WIP or MPP were added in Table 1

Answer: The text about soil sampling was supplemented with new information *(Rows: ????)

“Soils sampling was performed according to Russian National Standard [21]. To characterize the changes in soil contamination with depth samples were collected from the layers 0–5 cm and 5- 20 cm in 15 park recreational zones in Moscow located in the near vicinity of the Thermal Power Plants (TPP), Waste Incineration Plants (WIP) as well as Moscow Polymetalic Plant (MPP) (Fig. 1, Table 1). At each site three sub-samples were collected from an area of about 5 x 5 m. For further elemental analysis samples were cleaned from foreign objects (leaves, the remnants of grass), homogenized and dried at 105 ºC”. Each soil replicate was prepared and analysed s eparately and the data in the paper are presented as mean values ± standard deviation.”

  Remark: Lines 113-121. Authors must include, as supplementary material, the certified values for all analysed elements present in the standard reference materials used. Where do all PCEs analysed in soils samples certified in any of the SRM? Considering the high thermal lability of Hg, did you check if Hg could be lost after drying at 105ºC?

Answer: we have included in the Table 2SM-Supplementary Material, as well as in the subsection: Determination of the soil samples elemental composition

  Remark: Lines 154-162. The use of parametric statistical test could be not adequate if requirement about normal distribution and homogeneity of variance were not satisfied. More detail explanations about what test, and in what context, were they used. Otherwise, the robustness of the statistical results could be put in question.

Answer:It is absolutely correct. Thank you. We by mistake have used some parametric test without proving that the data are normally distributed. For this reason we have removed this paragraph, replacing by by a short comment concerning the use of nonparametric Wilcoxon W test, for both major and trace elements.

 Results and Discussion

  Remark:  Line 166. What do you mean with “soil basic material”? This is not a term usually used in studies on soil pollution. Please, add some explanation.

Answer:

  Remark:  Line 171-173. Considering the abovementioned comment regarding the usefulness of UCC for EF, CF and Igeo values, a similar criticism can be applied to these results. Table 1SM was not found in the submitted manuscript. (Neither Table 2SM, Table 3SM and Table 4SM).

Answer: We have included in the .zip file the Supplementary Material as .xls file.

Remark: Lines 175-178. “Spearmint´s”? Please, check. What is the true finding suggested in line 179? Please, authors must be much more explicit. If they want to say that there is no difference in major element concentrations between 0-5 and 5-20 soils layers, them let´s say something like this. In what extent that normalization of mass fraction of major elements to the UCC contents could hint differences between soil layers? Did you check such differences with non-normalized mass contents?

Answer: We have checked both variants. The correlation coefficients were the same.

Remark: Regarding Figure 2, what about fig 2e? Why figure 2 goes from 2d to 2f?

Answer: We have corrected.

  Remark: Lines 218-220. Please, check this range of contents for trace elements. In addition, organic matter also plays a key role in the accumulation of trace elements in soils, especially in the uppermost soil layers where more organic matter is usually accumulated. What about the role of soil organic matter in the mass fraction and ecological risk indices for trace elements?

Answer: We have checked (see Table 1 SM-Suplementary Material). Concerning the organic matter, at this moment we were interested only in evidencing the local contamination. The correlation between organic matter and the presence of PCE could be the subject of a future work, but in this case it would be necessary to investigate, at a higher sampling rate the vertical profile of TOC and the mass fraction of chosen PCE.

  Remark: Line 229. There is a typo in this line.

Answer: We have removed the entire sentence.

  Remark: Regarding Figure 3, the position of some trace elements cannot be distinguished in figure 3a. What is the blue shadowed area in figure 3a? Please, remember that figure must be auto- explicative. In these graphics appear a lot of details which are not explained in the figure caption (error bars?, what are the continuous (3a) and dashed (3b) lines?, what do mean the dashed ellipses in 3d? and so on…

Answer: We have add to legend: “Blue strip in the bi-plot (a) represents the 95\% confidence interval. Dotted ellipses in bi-plot (d) illustrate the different types sources of rocks”

Remark:  Line 240. Do you mean fig 3c when you refer to Th/Co vs La/Sc? Please, check.

Answer: We have corrected. Thank you.

  Remark: Lines 257-262. The hypothesis that authors try to explain must be much more explained. It is quite difficult to extract from figure 4b what the really want to mean.

Answer: We have discussed in more details the significance of Fig. 4b and 4c in explaining the continental nature of mineral phase of investigated soils.

  Remark: Lines 280-300. It is extremely difficult to follow the reasoning of the authors for several reasons. First, no allusion to true results (values) of EF appear in the text (see as example lines 293-294 when authors talk about EF of Hg). Second, authors talk about EF of elements from which reader have not values in the text or in figures. Third, it is quite difficult to follow what is showed in figures when soil samples in figures and soil samples in the text have different names (from 1 to 15 in figures and names remember anthropogenic point sources such as WIP Nº or TPP Nº are used in the text). Perhaps unifying the nomenclature of soil samples would favour the understand.

Answer: We have re-designed Fig. 5 including the names of samping points.

  Remark: Lines 307-308. I think that, in addition to vehicles, other anthropogenic sources could account in a better extent for the moderate pollution of Hg. The emissions from thermal power plants or waste incinerators are more likely to contribute in a greater extent than vehicles to Hg pollution in the studied soils. I think that, at least, these other sources should be also take into account to explain such moderate values of Igeo for Hg in some soils.

Answer: Thank you for this advise. We have include a small comment on this regard.

Remark: Lines 311-323. There is no discussion about CF values as these lines only represent a somewhat confusing description of results for this ecological risk index.

Answer: We have completely reformulated this section (purple and red color)

 Conclusions:

  Remark: Conclusions should be rewrite according to the necessary improvements in the text.

Answer: We have reformulated the Conclusion section (red ink)

 

Reviewer 4 Report

Dear authors,

There are numerous grammatical and typographical errors, many which have been identified in the annotated manuscript.

The map from Figure 1 should show coordinates or geographic reference.

Given that the lithological substract is such an important control for the soil geochemical signature, a brief geological setting of the study area would be appropriate in the introduction. This context would also allow to exclude or consider possible influences from mining processes and activities in this soil enrichment. Some of the contaminant elements that are refered in the manuscript can be naturally enriched in soils surrounding mining deposits of metals or coals.

The sampling and analysis methods are described quite thoroughly, but please see comments in the annotated manuscript where clarification is required.

Regarding the results and discussion, the authors should consider the regional geologic context in the overall discussion.

Some corrections and suggestions were added to the revised copy.

Thank very much for your effort,

Best Regards

Comments for author File: Comments.pdf

Author Response

 Dear Reviewer,

Thank you for the time you have spent as well as for the quality of your remakes and advices

Here are my our answers (correction in blue ink)

Remark:There are numerous grammatical and typographical errors, many which have been identified in the annotated manuscript.

Answer: we have tried to correct all of them

Remark: The map from Figure 1 should show coordinates or geographic reference.

Answer: We have included a new map cotaining more geographic refrences

Remark:  Given that the lithological substract is such an important control for the soil geochemical signature, a brief geological setting of the study area would be appropriate in the introduction. This context would also allow to exclude or consider possible influences from mining processes and activities in this soil enrichment. Some of the contaminant elements that are refereed in the manuscript can be naturally enriched in soils surrounding mining deposits of metals or coals.

Answer: We have mentioned in text that in the Moscow vicinity there are no mining deposits of coal and metals. These are far away in the Ural region.

Remark: The sampling and analysis methods are described quite thoroughly, but please see comments in the annotated manuscript where clarification is required.

Answer See please the following answers

Remark: Regarding the results and discussion, the authors should consider the regional geologic context in the overall discussion.

Answer: we have included mor comments on this subjact (rows ???), blue ink.

Remark: Some corrections and suggestions were added to the revised copy.

Remark on pdf file: Given that geochemistry is strongly influenced by pedogenic effects on regional bedrock a short geologic context should be included

Answer: We have induced a short note on this subject : All these findings were in good agreement with the geochemistry of the central part of Russian Plain, covered with sediments remnant of Precambrian continental crust composed of magmatic and metamorphic rocks [35]

Remark on pdf file: Given that Hg is a volatile element and was one of your targets, it seems a high drying temperature. Is there a particular reason to choose 105ºC?

Answer: we have included the followings: To avoid Hg loses during sample preparation, a certain quantity of collected soil was dried only at 40 ^oC, while the mercury mass fractions in samples was determined using a Milestone DMA-80evo Direct Mercury Analyser (Milestone Srl, Sorisole, Italy) (\ url{https://www.milestonesrl.com/contact-en}, accessed 12.02.2023).

Remark on pdf filr: The map should have geographic reference, I suggest a coordinate grid.

Answer: we have included a new map with all geographic coordinates

Remark on pdf file: Is this a certified laboratory? If so the respective creditation info should be included.

Answer: yes, the used thechniques is certified: Certificate of attestation of measuring technique №348/2021-01.00115-2013 issued on May 31, 2021 by Federal State Budgetary Institution All-Russian Research Institute of Mineral Raw Materials named after V.I. N. M. Fedorovsky, and this mention wes included in the manuscript

Remark: Needs more detail on the Hg determination Procedure. How many samples were taken? Control samples?

Answer: we hav included these details in the manuscript as well as in the Table 2SM – Supplementary Material

Remark: Given that different stable elements can be used, maybe explain why Sc?

Answer: Sc is a third group incompatible element, with almost no industrial use, so that it is one of the reference element, especiallyas its presence can be demerited with high accuracy and precision by INAA

Remark: Before the first time the abbreviation are used should be explained (fully written)

Answer: We have introduced all acronyms in text at the firs use, but as the MDPI template include this paragraph, we hav inclde also at the end of the manuscript.

Thank very much for your effort,

Best Regards

We thank you for the useful and valuable comments.

Round 2

Reviewer 3 Report

The authors did a good job accomplishing and solving most of issues mentioned in the previous revision. However, some minor issues are still pending and need to be clarified.

Abstract:

In spite of previous comment regarding the lack of significant results in the abstract, the authors only include one result. This is not enough if authors want to gain the attention of readers. So, they should improve this issue definitively.

Introduction:

It is still lack background information about what are the ecological risk indices and what are their advantages when PCE contamination in urban soils needs to be assessed. Authors scarcely change the aims of the study in spite this was recommended.

Material and Methods:

Lines 99-100. Why were these soil depths (0-5 and 5-20 cm) selected for this study? This information was required in a comment on version 1 but it was not answered.

Section 2.4. Authors answered they changed the text regarding statistics in the new version of the manuscript but, it remain the same. Some issues regarding this appear in lines 193-195, but they should appear in the section that describes all the statistical test carried out.

Results and Discussion

The question regarding “soil basic material”, now in line 182 is still missing. I presume it is only a question of writing with the adequate word.

Tables in the supplementary material must be properly identified. As example, in the xls file nothing have the names Table 3Sm o Table 4SM…this is important to facilitate the accessibility and understandability of the results to readers.

Regarding the author´s response to comment of lines 218-220 (original version), I consider relevant to include some comment about the effect of organic matter as it favours metal accumulation in soils modifying the final values of ecological risk indices. The inclusion of this information will not prevent to make an additional paper relating metals and organic matter in these soils, and it contribute to a better understand of metal accumulation.

Author Response

Dear Reviewer,

Thank you for your interest and help in revising our manuscript.

Reviewer 3 (Changes in Violet Ink)

 

The authors did a good job accomplishing and solving most of issues mentioned in the previous revision. However, some minor issues are still pending and need to be clarified.

Abstract:

Remark: In spite of previous comment regarding the lack of significant results in the abstract, the authors only include one result. This is not enough if authors want to gain the attention of readers. So, they should improve this issue definitively.

Answer: Thank you for this remark. We have included (rows 10-17) the followings:

Contamination Factor (CF), Enrichment Factor (EF), Geoaccumulation Index (Igeo) and Pollution Load Index (PLI), all of them defined with respect to UCC, were used for a comprehensive evaluation of the soil pollution with presumably contaminating elements Cr, Ni, Zn, As, Sb and Hg. Among them, only in few places, CF reached a maximum values of 5.9 for Hg, EF of 13 and Igeo of 3.12, both for Sb, but in different places, pointing towards an uneven distribution of contaminated areas. As, for the majority of places, the same indices were below or around the contamination thresholds, only for some locations the PLI exceeded 1.05, suggesting a moderate contamination localized in the vicinity of few thermal power plants.

Introduction:

Remark: It is still lack background information about what are the ecological risk indices and what are their advantages when PCE contamination in urban soils needs to be assessed. Authors scarcely change the aims of the study in spite this was recommended.

Answer: Thank you for this remark. We have included (rows 44-54)

For a real assessment of the contamination degree, at present there are in use more ecological risk indices, all of them permitting a numerical comparison between the amount of a considered PCE in environment and a reference threshold, which can be established by some national regulations or correspond to a pristine, uncontaminated environment. In the last case, the Upper Continental Crust (UCC) [15] can be regarded as the most conservative approach. In view of this, the actual ecological indices refers either to individual PCE such the case of Enrichment Factor (EF), Contamination Factor (CF), as well as Geo-accumulation Index (Igeo) or simultaneously to more PCE as the Pollution Load Index (PLI), all of them presented in detail in the next sections. Moreover, having numerical values, these indicators allow for a comprehensive statistical analysis of the status quo of the considered environment

Material and Methods:

Remark: Lines 99-100. Why were these soil depths (0-5 and 5-20 cm) selected for this study? This information was required in a comment on version 1 but it was not answered.

Answer: we have explained in this version (rows 113-114): ….to characterize the changes in soil contamination during this time, at each sampling point the samples were collected ….

Remark: Section 2.4. Authors answered they changed the text regarding statistics in the new version of the manuscript but, it remain the same. Some issues regarding this appear in lines 193-195, but they should appear in the section that describes all the statistical test carried out.

Answer: It was our omission. We have corrected by including the reference to t, F, Mann-Whitney, or Anderson-Darling testes, as inadequate for our case. (rows 186-191). Thank you.

Results and Discussion

Remark: The question regarding “soil basic material”, now in line 182 is still missing. I presume it is only a question of writing with the adequate word.

Answer: Thank you. We have replaced by “mineral component”

Remark: Tables in the supplementary material must be properly identified. As example, in the xls file nothing have the names Table 3Sm o Table 4SM…this is important to facilitate the accessibility and understandability of the results to readers.

Answer: We have renamed all tables in Supplementary Material, e.g. 1SM, 2SM and 3M. Thank you.

Remark: Regarding the author´s response to comment of lines 218-220 (original version), I consider relevant to include some comment about the effect of organic matter as it favours metal accumulation in soils modifying the final values of ecological risk indices. The inclusion of this information will not prevent to make an additional paper relating metals and organic matter in these soils, and it contribute to a better understand of metal accumulation.

Answer: It is true. Thank you for this remark. We have included a short comment (rows 295-302) on this matter.

In investigating the presence of trace elements in soil, it should be evidenced the role of the organic matter which, depending on the local conditions, can favor either their immobilization or release [38]. In the presence of organic matter, metal ions form a great variety of chelates or organo-metallic complexes which further control their availability for plants, microbiota, ground water of their long distance redistribution [39]. According to [40], the soil organic matter, due to its ability to form chelates, maintains the content of inorganic contaminates in soil, but significantly reduces their bioavailability, making the environment in essence harmless.

Once more, Thank you

Authors

Reviewer 4 Report

Congratulations to the authors. They did a great effort to improve the manuscript, and a better, clearer version was submited. 

Best regards,

Author Response

Rear Reviewer,

Thank you for your interest, advice, and encouragement in reviewing our manuscript.

Our best wishes,

Authors