Decadal Variation of Polycyclic Aromatic Hydrocarbons (PAHs) in an Area Contaminated by Coal Gangue Dump: Emphasis on Concentration, Profile, Source and Carcinogenic Risk

Round 1

Reviewer 1 Report

The authors analyzed the PAH concentrations in a coal gangue sample along with PAHs in downstream soils and sediment. In general, there was a decrease away from the coal gangue site. In relation to previous data there seems to be a decrease in PAH concentrations and the composition (based on PAH isomer ratios) indicates that the PAHs are of pyrogenic origin. Presumably this is because of a lesser input from the coal gangue and the PAHs are now coming from sources such as cars.

There are definitely language issues in this manuscript. This is normally not a problem, as long as the reviewer can understand the general meaning of the sentences. However, there are many instances where I could not understand the meaning, no matter how hard I tried. I could comment about specific lines, but there are no line numbers and to expect the reviewer to go through the manuscript, line by line, and describe where the critical feedback should be is an extremely onerous task. This made the review very frustrating and time consuming.

From what I could understand, there was one coal gangue sample taken (J1) and the rest are soil and sediment samples. I understand that taking samples is difficult and the extraction takes time, especially when Soxhlet is used. However, the lack of replication does make the manuscript and its conclusions quite weak, though I think we should be lenient on this.

However, I found the statistics used difficult to comprehend and the conclusions are going to have be clarified. Unfortunately this is a manuscript that is still in the draft stage and will require major revisions and another round of review.

Introduction:

You mention that Masclet et al describe five main evolution processes. While they are interesting, having read your manuscript, there really is no way of knowing how the PAHs found in the downstream soil and sediment got there. So I think just simply saying that the PAHs can be deposited through the air or through run off is sufficient. I mention this because there are many details in the introduction that are superfluous and this entire section could be much shorter. Just provide whatever information you think will effectively contextualize your study.  

Materials and methods:

As I mention earlier, I think the lack of replication, especially for the actual coal gangue site (JL1) is a major problem. It is a problem because the differences between JL1 and JL2-6 are not really clear, as I found out in the results section. The concentrations are not that different.

3.1.

This is I think somewhat problematic. I understand that taking samples is difficult, but it is difficult to make strong statements on the trend of PAH concentrations when there is only one sample taken from the coal gangue. Also, I think there is going to have to be a stronger argument made for the coal gangue being the true source of contamination in the area. Are there other potential sources? Keeping in mind the mobility of the light weight PAHs, it is possible that these come from other sources (i.e. traffic). Have these factors been considered?

You have taken the pains to measure the background concentrations (B6-40) but have not commented on them. They are referred to as background in the methods section, but they seem to be generally consistent with the downstream soil samples (i.e. JL6 and 7). Is there anything to be said about these samples? One in particular is quite far away (40 km) and the PAH concentrations are quite low. I think this is a good data point, but there has been little said about this.

3.2. This section is unclear. I understand that the graphs show a “visual difference” between the current and previous results, but to be clear, is the non-statistically significant difference in the total PAHs based on JL1 to JL7? If the coal gangue and soil samples (JL2-6) are different samples, shouldn’t they be separated from each other for the statistical analysis? I ask this because it is not clear based on the description in the manuscript how this matched sample t-test was done. This section is going to require a lot of work to clarify, but it must be made clear to the reader how you did this analysis. Otherwise the reviewer cannot in good faith accept the results.

In terms of JL3 being higher than JL2, this type of variation can be expected when there was only one sample taken at each site. However, in your explanation of the results, I am not sure what you are trying to say in the last sentence of page 7.

Section 3.3. As for the PAH ratios, there is a growing skepticism among PAH researchers with regards to the utility of these ratios. In general, they are probably not that meaningful. However, because these are based on established methods, it is difficult to criticize their use here.

However, I am confused by what is being said in this section. You say that there is a conspicuous decline in PAH concentrations and that this relates to more effective environmental management. This may be true, but in your previous section (3.2) you say that there was no statistically significant change in total PAH concentrations. At least, that’s what I think you are saying, though I am not quite sure. How can you say for sure that there have been decreases in these PAHs, based on better environmental management?  

Conclusion

The word “supergene” has been used here (and I think elsewhere in the manuscript). What do you mean by this? I have no idea what this is supposed to mean in this context. 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The work presents the evolution of PAHs pollutants in terms of concentration, profile, source, and carcinogenic risk in an area contaminated by a coal gangue dump.

Some aspects should be considered:

-         First of all, the novelty of the study is not argued sufficiently

- What's “matched sample t-test” mean and which is its interpretation in terms of MMW-PAHs increasing (Table 2)?

-         What’s “Spearman’s correlation” mean? … more details are necessary

-         Even if the data on the calculation of the carcinogenic risks are presented in previous studies, for the reproducibility of the data, a brief description of how it is calculated would be necessary.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

This study provides significant input especially regarding the carcinogenic risk, however, requires minor editing prior any publication.

Introduction section: The problem statement and objectives are not clearly highlighted.

Section 2.1: Please state the longitude and latitude coordinates of the coal gangue dump site.

Conclusion Section: The authors are highly suggested to delete the numbering in the first until fourth paragraphs.

 

Author Response

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Author Response File: Author Response.pdf