Assessment of Distribution of Potentially Toxic Elements in Different Environmental Media Impacted by a Former Chlor-Alkali Plant

Round 1

Reviewer 1 Report

The authors of the manuscript investigated the accumulation of Hg with other metals in soil, water and sediments near a lake affected by a former chlor-alkaki plant.

According to the references cited in this manuscript, PTEs accumulation in this region has been investigated in several studies. So, the most important thing for the authors of the present study should be, to defend your work. Why is your work interesting? What is the difference between your work and the published ones? But the authors failed to answer these questions in the introduction section.

The whole manuscript was very much lack of logic and clarity. I hope the authors will re-write the whole manuscript to make it more understandable.

The results and discussion section should be written in the sequence of results+discussion. However, in most parts of this manuscript, the sequence is discussion+results. This makes reading difficult. The authors compared their results with previous publications about the pollution in this area, but it seems that nothing novel about the present study was found.

For the figures, the authors used very similar codes for lake and groundwater (such as in Figure 2), this makes the distinguishing of water and groundwater samples difficult.

Also, do not begin a sentence with value (such as in Line 283), use the word for the value.

Section 3.1, the results should be indicated in a table or figure, but here the authors only depicted them in words, this is not common for papers.

Author Response

We thank the Reviewer for their comments and time. Please find attached our responses.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper aims to the assessment of mercury (Hg) and other selected potentially toxic elements in different environmental media impacted by a former chlor-alkali plant. To be honest, I can not find the new findings in this manuscript.

* The necessity and innovation of the article should be presented in the introduction.

*It is suggested to present the structure of the article at the end of the introduction.

* The major defect of this study is the debate or Argument is not clearly stated in the introduction session. Hence, the contribution is weak in this manuscript. I would suggest the author enhance your theoretical discussion and arrives your debate or argument.

* It is suggested to compare the results of the present research with some similar studies which is done before.

*Please revise your conclusion part into more detail. Basically, you should enhance your contributions, limitations, underscore the scientific value-added to your paper, and/or the applicability of your findings/results and future study in this session.

Author Response

We thank the Reviewer for their comments and time. Please find attached our responses.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Ref. 1449707,

Assessment of mercury (Hg) and other selected potentially 2 toxic elements in different environmental media impacted by a 3 former chlor-alkali plant.

You paper is very good. Even though it does not present a novelty in detection of Hg and other PTEs, is provides and important update for a strong affected region in Kazakhstan. I have a few minor suggestions bellow:

Abstract: OK

Introduction:

I think that all figures are lacking a bit of resolution, if they are already on 300dpi, try increasing to 600. For figure 1 make the border of Pavlodar also a bit more black, it will be better to see its limit.

Your introduction is good, but there is no novelty regarding to HG/PTEs detection (not a new method for example). However, an updated report is especially useful for the pollution prevention management, as stated on the special issue, so this is ok for me.

Materials and methods:

When you mention the climate of the Pavlodar region you could use a reference like the Köppen climate classification system (line 153).

Results and discussion:

Try not to split tables into two pages (when possible). This section is pretty good, all the methods used and results obtained are well discussed and referenced well. I just noticed that some of your references are a bit old. Before the final version try to update them as much as possible (some core ones must be maintained).

Best regards,

Author Response

We thank the Reviewer for their comments and time. Please find attached our responses.

Author Response File: Author Response.pdf

Reviewer 4 Report

Authors present results of measurement of Hg and another potentially toxic elements (PTEs) (As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sb, Se, and Zn) in the soil, sediment, and waters near area where certain chlor-alkali plant (CAP) operated from 1975-1993 in Pavlodar city (North Kazakhstan) . Presented data are short of detailed characterization and interpretation. The paper does not contain any new and interesting information, research not conducted correctly. 

1) Title: “Assessment of mercury (Hg) and other selected potentially  toxic elements in different environmental media impacted by a former chlor-alkali plant”

Assessment of what? Content? Health/environmental risk?

 Introduction

2) The introduction contains an information about Hg pollution of the environment in various areas around the world. However, the introduction contains limited information about Pavlodar and the current situation, about previous studies and current (including official) environmental monitoring. There is no information about sarcophagus which has been built, information about technical possibility of the migration of elements into groundwater and the Irtysh River.

3) The authors write that 23 PTEs were dumped into the lake, but Hg and 12 more elements were chosen for the study. Why?

Methods

4) Authors should add more information about quality control and assurance: certified reference materials, recoveries, limit of detection and information how is the LOD defined.

Results

5) Hg contamination in Table S1: 0.00 ± 0.05, 6.98 ± 0.00 …. Cd: < 0.00, 0.27 ± 8…. As: 7.40 ± 17, < 0.07, ≤ 5.01…. How it can be? These results are highly questionable.

6) Cr is absent in Table S1, it is present in Table S2 only in 2019. Not measured or not determined?

7) How it can be seen in the map, the lake and pond are not connected by surface waters. Are there migration routes to groundwater? The Irtysh River? If no, why they were investigated? In the sites below Pavlodar, is the pollution connected only with the urban enterprises?

8) Line 429. Why the soil concentrations were compared with the background ones in Canada? Canadian soils are associated with glaciation, Pavlodar is a highland. Why weren't used the background concentrations of soils in Kazakhstan and Russia?

9) Line 460. Arsenic concentrations were below background levels. This proves that the background concentrations are wrong.

10) The manuscript does not contain environmental risk assessments, health risk assessments, does not show significant differences from previous studies, does not contain modern methods for identifying pollution sources (principal component analysis, cluster analysis, self-organizing maps). I recommend to use these methods.

Author Response

We thank the Reviewer for their comments and time. Please find attached our responses.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors revised their submission. I still have the following comments,

1. i) The whole manuscript is wordy, please make it shorter, simpler and clearer.

E.g, The first three paragraphs can be combined into one and be written with much less words, the present three paragraphs are telling the similar information, and these information are fundamental to environmental scientists.

The conclusions and recommendations section is also too long.

Ii) The data quality should be described and discussed. I noticed that the authors used certified reference materials in the work, but I tend to believe that they are solutions, in stead of real soil, water or sediment samples. So, this makes the results questionable. For example, the low Pb (<10 for most samples in first several trips in Table S2), Cu (<0.2 mg/kg for most samples) and Cd concentrations (<0.00 mg /kg for ) in soil are not reliable very much, as we know, the background values of these three elements in global soils are about 20-30, 20-30 and about 0.1 mg/kg, it is not likely to find soils with so low concentrations. I tend to believe there was mistake of the analysis of samples May 18 to Oct 18, as we can find obvious different results of these samples with those of later sampling dates. But the results of Hg seems in agreement between different trips. Maybe the authors should consider removing results of these three trips from the manuscript.

Please explain how can you get results as low as 0.011 mg/kg in Table 3 for soil Cd when the LOD is about 0.11 mg/kg in Table S5?

Still, express your data as tables or figures, then describe it. There is not data indication for pH and EC at present.

Iii) The figures may be made better, you can use different shapes (circle vs triangle, for example) for different samples.

Iv) In the introduction section, please describe what has been done about the study area, and tell the audience that there is a need to do the present work, based on these information, as in Lines 113-114. In the R+D section, compare the results of the present work with those in references, to show that you made a progress.

60. v) Lines 124-138 may be moved to the location after Line 60.

1. vi) In the M+M section, more information is needed, for example,

For soil sampling, from a small area, how small? How did you sample sediment?

Line 218, did you freeze these samples?

Line 223, this is not dilution.

L266, did you dilute before filtering?

Vii) other comments,

Write with carefulness, such as, In Line 302-313, you mentioned the organic material affection the behavior of Hg, then you described the Hg results, but you did not discuss how the results will affect the behavior of Hg in the samples.

In Line 23, there are three “around”s.

Lines 113-120, I do not think these section help much.

The title may be made shorter, like,

Assessment of distribution of potentially toxic elements in different environmental media impacted by a former chlor-alkali plant

Author Response

Please see the attachment, thank you.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript is now good enough to be accepted.

Author Response

Thank you for accepting our manuscript and for your efforts.

Reviewer 4 Report

Dear authors,

The reviewer may have  own opinion and disagree with the opinion of the authors, however, I understand that it is the study of the authors and you can do own conclusions. I can agree with many issues, but there are two main issues with which I fundamentally disagree (1) using the background content of TEs in Canada for study of Pavlodar, (2) the results presented in Sup.data. Please, look the details below.

1)Trace elements are defined as any element that is present in relatively small amounts in soils and rock, either natural or anthropogenic. Background trace element concentrations in soils are generally considered those that are less than 100 mg/kg. Trace elements naturally accumulate in the soil during the pedogenic weathering of geologic parent materials. Trace
element concentrations differ between various rock types; therefore, the concentrations differ between the soils that form over the various rocks.  
 Quantifying background trace elements in soils is valuable from an environmental regulatory standpoint. Reliable data are needed to determine acceptable regulatory levels in cases of soils affected by industrial processes. The U.S. Environmental Protection Agency (EPA) regulates trace element affected soils by establishing concentration guidelines for risk
based studies. Incorrect trace element data can potentially lead to mandated cleanup guidelines for trace elements in soils that fall below levels that are realistically attainable based on naturally occurring concentrations. I can not agree that parent materials in the Pavlodur are the same with Canada. Also Dark chestnut dry steppe soils are characteristic of Pavlodar. There are no the same soils in Canada, please, look here https://soilsofcanada.ca/

The mistake in background trace element concentrations is very serious mistake for risk assessment of TEs contamination.

2) Sup.data. The content of TEs can not be less than 0. It never can be. It can be less than detected limit (DL). Also, id you use one metod - content can not be less than  0.06 ( May 2018, ID 2505-P-Sed-02, As) and less than 4.85  (May, 2018 ID 2505-P-Sed-01, As). How it can be? If less- always less than DL. After that I look Table S5 and see that DL for As in 2018  is 6.46. So - what did you mean than write less 0.06 or less 4.85? How was it determed? And many values in Sup.dats are strange. Another ex. - 2509-P-S-04, May 2019 - Cu content less than 98.9. But 2018 DL for Cu is 19.6. How can it be? Another big problem is +/-SD. For ex. 2505-P-S-13 Co-content was 4.50 ± 0. What did you mean? There was not any SD? 

How credible are the study results? 

 And, in conclusion, response to comment 10:
"We thank the Reviewer for pointing this out and definitely agree that site assessment is complete with a detailed risk assessment. As this paper is already very long (24 pages, with 9 tables and 6 figures excluding Supplementary Material), we have prepared and submitted a second
paper to the same journal special issue focusing on the probabilistic and deterministic human health risk assessment. In other words, we divided the site assessment into two papers due to length issues"

This answer is not sufficient. Obviously, the authors think that the information provided in the manuscript is sufficient and they are not interested in the reviewer request for the completion of the text.

I can agree that health risk can be aim of  another MS. But how I understand the main aim of the present MS was environmental risk assessments, was not it? But how was it quantified? Where is the evidence for the sources of mercury and TEs. 

The MS contains a very long introduction - 6 pages. It can be shortened. Also  I recommend to transfer  the Tables 7&8  in Sup.data because they do not contain results obtained by authors. I recommend to include (at least) a quantitative assessment of environmental risks and principal components analysis with regression analysis to identify sources, it is currently the best method for identifying pollution sources. "The gold standard" for any study of TEs is to separate natural and anthropogenic sources of TEs, as well as provide evidence of specific anthropogenic sources and assess environmental risks.

Author Response

Please see the attachment, thank you.

Author Response File: Author Response.pdf

Round 3

Reviewer 4 Report

MS was corrected. I have only few recommendations.

• Please, make some correction in values of the experimental results

The numerical values of the experimental results must be written according to specific rules.

The number of significant figures in the experimental uncertainty is limited to one or (when the experimental uncertainty is small, e.g., ± 0.15) to two significant figures. You should not use more than two significant digits.

The best estimate (usually the average value) and its uncertainty (experimental error)must always have the same number of digits after the decimal point. Forexample, 2.4 ± 0.16 implies that the result lies in the range 2.24 – 2.56. The correct way is 2.4 ± 0.2.

For ex.: now in Table S6 authors use three significant figures, my recommendation is to use, at least, only two, more better – one.

In another Tables in Sup. data, for ex.:

Please, check all MS

• Table 2.

In lines 292-299 authors wrote

maximum permissible concentrations have been established worldwide by various governments (e.g., Canada and Kazakhstan) and health agencies (e.g. World Health Organization (WHO)). In comparison to the limits proposed by WHO (2007) and Canada (MDDELCC, 2019), the national standards proposed by Kazakhstan (MEPRK 2004) are more stringent and aim to reduce Hg concentrations in the environment but not its emissions (Guney et al., 2020). In the present  study, the concentrations of Hg were first compared with the local national standards (Table 2) to identify the level of contamination in soils, sediments, and water in the Pavlodar 299 region.

But now there is no limits proposed by WHO (2007) in Table 2. Please check text or Table 2.

• Line 333

Authors write

“THg levels, indicating the retention of Hg by organic matter in the soil”

I recommend to add a short discussion on how it  affects the ecotoxicity of mercury

• Table 6.

TEs didn’t correlate with Hg, so they had different sources. Do authors have any assumptions about the sources of TEs pollution in hot spots?

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf