Assessment of Heavy Metals Accumulation in Soil and Native Plants in an Industrial Environment, Saudi Arabia

Round 1

Reviewer 1 Report

The manuscript has been written well and supported with sufficient experimental data. The study has investigated the heavy metals concentrations in soils and native plant species in an industrial zone in Riyadh and also assessed the status of heavy metals contamination in the above said area. However, the statistical analysis needs to be studied in the manuscript. Please consider the following comments to improve the manuscript.

* Abstract should be rewritten by detailing the aim and concept of the study. The abstract should state briefly the purpose of the study, the principal results and major conclusions.

*Provide significant words which are more relevant to the work in logical sequence as ‘keywords’.

* Introduction is very general and need to be elaborative to explore the actual philosophy to design the experiment. The introduction is insufficient to provide the state of the art in the topic. The originality and novelty of the paper need to be further clarified. What progress against the most recent state-of-the-art similar studies was made in this study?   

* Justify the novelty in introduction and discussion, as well.

*Line no 105-120; remove these unwanted lines.

*Improve the discussion part by adding more supporting data from the literature like https://doi.org/10.3390/ijerph19031596

* Line no 198-201; kindly discuss the statistical analysis section properly.

* It would be necessary to develop more bioinformatic/statistical analyses in the present study. The information give is very scarce. 

* Authors are suggested to add discussion by explaining trends in the obtained results along with the possible mechanisms behind the trends.

* It is strongly recommended to add a subsection, 'practical implications of this study,' outlining the challenges in the current research, future work, and recommendations, before the conclusion.

* Pls. conclude with more focus on the major outcomes of the paper.

* Check and correct grammatical and space errors throughout the article.

Author Response

Please see the attachment. 

Author Response File: Author Response.docx

Reviewer 2 Report

The authors described the methodology of soil and plant sampling and analysis in a clear and detailed way. The results are presented in a satisfactory form. I have a few remarks and suggestions to improve the quality of this paper.

Page 2, row 53 – finish the sentence

The introduction is too long. The same information’s are repeated several times, arranged in a different way

Page 2, row 45 – 74 - In this part of the paper, you repeat the same thing several times, that is, you talk about the impact of HMs on human health and the impact of industry on the presence of HMs. That's superfluous. Get those sentences out.

Page 3, row 79 - eject redundant points

Page 3, row 77 – 80 - reference is required

Page 3, row 90 - Based on this sentence: "A previous study conducted to assess soil and plant content of HMs in the Al-Qassim region found that the concentration of Cd in Lactuca Serviola shoot was (73 mg · kg − 1) and as a result, could be a candidate for a hyperaccumulator of Cd " it cannot be concluded that the plant is a hyperaccumulator of Cd. If the cited paper presents bioaccumulation factor values, please state this in your paper.

Page 3, row 91 - delete brackets

Page 4, row 105 – 120 – delete this text

Page 5, row 129 - which device you used to sample the soil?

Page 9, row 215 - The concentrations of HMs (Cd, Cr, Cu, Fe, Pb, Zn, and Ni) in soils collected from the 12 sites of study area are summarized in Table 3, 4 and 5. – Tables 4 and 5 show concentrations in plants, not in soil

Page 9, row 222 – 224 – For the first time you use the symbols S1, S2 ... Please explain their meaning

Page 9, row 222 – 225 – In this part: “The comparison of the mean values showed that contents of Cd in S1 and S2 and Ni in S4 and Pb in S2 and S12 in the study area were found to be significantly (ܲ < .001) higher than those in other sites. In addition, the results have shown the highest HMs concentration to be in sites S11, S7 and S5 which indicate a higher accumulation load from adjacent factories due to local activities.“ - you have contradictory claims. On the one hand, you claim that the highest concentrations of certain metals are at sites S1, S2, S4 and S12 and on the other hand that the highest concentration of HMs is at sites S11, S7 and S5.

If you meant the total concentration of HMs please change it as we never talk about the total concentration of heavy metals.

Page 9, row 225 - Please provide information on what type of industry is present in the observed area

The title of Tables 1 and 2 is above the table, and Table 3 is below. It should be the same everywhere.

Table 3 and Table 5 - It is impossible for the value of the standard deviation to be n.d. Change that.

Page 11, row 244 – reference is missing

Page 11, row 252 – reference is missing

Page 13 and 14 - it is not clear to me what the marks a, b, c, d, e, f ... mean in figures 4

Page 15 - please provide an explanation of the impact of the industry type on the Contamination factor (CF) and pollution load index (PLI) in the study area

Page 18 - In conclusion, as a reason for contamination, you cite many sources of these elements resulting from many production activities in addition to heavy traffic where the estimated locations are located in a dense industrial zone. I suggest that you describe in more detail the industrial zone where the samples were taken and that you draw a conclusion about the source of contamination based on the present industrial activity.

Comments for author File: Comments.docx

Author Response

Please see the attachment. 

Author Response File: Author Response.docx

Reviewer 3 Report

In this study, the authors investigate levels of heavy metal contamination in soils and plants from sites in the city of Riyadh, Saudi Arabia. Additionally, the authors use plant results to identify plant species capable of the greatest heavy metal uptake as candidates for phytoextraction and site remediation. I think this is an important topic of research impacting both the environment and human health. Below are my general and line specific comments.

 

General comments:

• More detail is needed in the methods. There is no clear description of how metal concentrations were determined in either the soil or plant material. Additionally, I have some line specific comments below indicating where more detail could be provided.
• Results could be more clearly presented. Only one results figure is shown (figure 4) while all data are presented in tables. I think creating figures would be more helpful. Additionally, there is a figure 1 and a figure 4, but no figures 2 and 3. Are these missing or were the figures numbered incorrectly?
• More discussion is needed overall. The “results & discussion” section reads almost entirely as just a results section. More interpretation of the impact of your results on things like human health, pollution management, and remediation would really strengthen the paper. There is also a general lack of context in relation to other studies – how do your results compare to past studies?
  • To help with the discussion, you may find it helpful to reorganize the order of the results & discussion to present HM concentrations in soil followed by EF, CF, and PLI results. Then move on to the HM concentrations in plants and BF results. This may help the story flow a little more logically.

 

Specific comments:

• Line 20: should read “were collected”.
• Line 23: should say “highly enriched”. Additionally, can you qualify what makes these “extremely highly” – are they above a certain enrichment factor?
• Line 27: “indicating a progressive deterioration” – can you provide some detail about whether there is a spatial pattern in these sites? Are some more centralized than others? Or perhaps closer to sources of industrial activity? I’m just curious because of the choice of phrase (e.g. “progressive”). Did you expect some sites to be more contaminated that others? If so, why?
• Line 39 (“HMs pollution is mainly related to human activities…”): Please provide a reference for this statement.
• Line 43: Are there common forms that these HMs are released into the environment as? For example, Fe is included in your list of heavy metals, but it likely won’t be released to the environment as pure Fe. Is it typically a specific iron oxide? What about the other heavy metals?
• Line 70: I’m confused about the use of “compartments” – are you saying that heavy metals persist in soils longer than any other part of the biosphere? Or do you mean that heavy metals persist more than other contaminants? If the latter, I think “compartments” should be “contaminants”
• Line 73: should say “function” not “functional”
• Line 106 – 119: This is text from the template and should be removed
• Line 132: How long were soils air-dried before sieving?
• Line 138 - 140: I’m confused about the purpose of these statements. What happened to the sample after filtering?
• Line 143: Was the same three-part sectioning of each site used during soil sampling maintained for plant analyses or were the three individuals chosen randomly from across the entire site?
• Line 146: What was the purpose of digestion? What was measured after?
• Line 163: Is it common to use metals in Earth’s crust as the reference when calculating enrichment factor? If so, please provide a reference.
• Line 165: The “[control]” sample is Earth’s crust in this case? If not, can you please clarify.
• Section 3.1.1: Where there any statistically significant differences in the chemical and physical properties of the different study sites? Additionally, a little more discussion would be helpful in this section. Can you provide more details about the sites? Are some more closely located to industrial sites? Any receiving specific management you expect might alter the abundances of HMs?
• Section 3.1.2:
  • A figure would be helpful – easier to interpret HM concentrations across sites when presented in a figure than when reading values in a table.
  • Statistics of each HM across sites can be presented in the figure as lowercase letters. While I know you provide a summary of the key differences, it is always helpful to visualize this.
  • Line 215: says HM results of soils are presented in tables 3, 4, and 5. But soil results are only shown in table 3 while table 4 and 5 are plant results.
  • More discussion is needed – this reads more like a results section with little interpretation of the results. Can you provide more detail about what these results mean for human health or management? Anything about the likelihood of contamination based on site location?
• Section 3.1.3:
  • Line 233: This very hard to follow with the values separated from their associated HM.
  • Line 238: I’m confused by this sentence – the Fe and Cu concentrations were highest in all plant species relative to what?
  • Can you provide more discussion? Any recommendations of how plants should be used for remediation based on your results?
  • Figure 4: Error bars should be shown on these figures. And this is presumably mg metal per kg plant? Please specify in the figure caption
• Section 3.3.1:
  • Line 281 - 282: I’m confused about the reference to another paper here when presenting your results. Can you expand on this statement?
  • Line 283: I think this sentence could be rewritten for clarity since 8.3% of soil samples showed extremely high Cu, Zn, and Ni – not necessary to repeat 8.3% multiple times

Author Response

Please see the attachment. 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have addressed all of my queries, therefore the manuscript may be accepted in its current form. 

Reviewer 3 Report

The authors did a very nice and thorough job addressing all of my previous comments. In particular, I think the inclusion of a “practical implications” section within the conclusions has greatly strengthened the impact of this paper. I have no further comments.