Chlorophytum comosum: A Bio-Indicator for Assessing the Accumulation of Heavy Metals Present in The Aerosol Particulate Matter (PM)
Round 1
Reviewer 1 Report
Dear authors,
I attached your manuscript with my comments. I hope that it will help you to improve the study.
First of all, I recommend revising the article by a native English speaker.
From the scientific point of view, I recommend you to:
- replace "atomic" with "optic" in "inductively coupled plasma atomic emission spectroscopy" - you have used the Optima 8000 which is an ICP-OES system;
- in the Introduction section, you must insert more references to cite the data sources and to avoid plagiarism;
- in the Materials and methods section, you must explain why you chosen the temperature of 130°C for samples drying;
- also, in the same section, please insert few information about the SEM-EDX system and work parameters;
- in the Results section (insert number 3 before the section title), Figure 3, you must insert data for the unexposed sample;
- also, in the same section, please insert EDX data and spectra for the particles from the leaves surface;
- in the Discussion section (insert number 4 before the section title), you must explain if the heavy metals contained in leaves come from the soil or from atmospheric pollution;
- also, you must explain the differences between collecting sites, which are the sources for those metals which recorded high values;
- you should explain why in the samples collected after 128 days you have lower values than the samples collected after 60 days (Figure 6) in the context of the Zn content in the PM reported by the ARPA monitoring station.
- the references list do not respect the journal requirements, you must change the font or something like that.
Kind regards,
IDD
Comments for author File: 
Comments.pdf
Author Response
We thank the reviewer for his comments and suggestions. The answers are reported in the attached file.
Author Response File: Author Response.pdf
Reviewer 2 Report
Introduction must be shorten. Some of the paragraphs, with argumentation, can be transferred to the discussion. Other have methodology details that are repeated in the Materials and Methods section. Some references on the legislation could be added.
In the Section "Materials and Methods", dates or times of incubations are not clear, as July samples seem to have been exposed only to 30 days (plus the 7 days that are not presented in the table). Authors must reformulate this section. The table has two similar rows for each location. Does this mean duplicates? Is would be interesting if there were two heights in each location, and I doubt that conclusions can be made about this parameter with these data.
Also in the "Results" section, authors state "Pb concentrations (not shown in this case) were much lower with a maximum at about 20 ppb.". If Pb was not considered as relevant, this must be clearly stated, because when reading the paper, the reader misses the table with Pb results. It turns the reading difficult. The "nor exposed plant" was mentioned in the "Materials and Methods" section but not very clearly.
The first paragraph of the section Results give us some more clues on the methodology. Why is this here and not in the previous section? And the authors state "The leaves were collected, as described in Table 1, at time intervals of 7, 30, 60, 128 and 165 days. " and that is not the case, as 7 days in not shown in the table, just mentioned in the legend of the table.
In line 211, the authors state "In order to assess the presence of particles on the leaves surfaces some measurements were carried out by SEM-EDS technique. ". Which leaves were subjected to these analyses? The results are nor clear in this section.
No details are given about the statistic analyses that enable to take conclusions about the significance of the differences between the different plants and sites.
A graphic is shown in the Discussion and this is a result.
Summarising; an interesting research has been designed (with some limitations) and there is a still good assemblage of results that deserve publication. Nevertheless, the manuscript must be completely re-written. The main problems are: organization of the text and tables and missing information.
Author Response
We thank the reviewer for his comments and suggestions. The answers are reported in the attached file.
Author Response File: Author Response.pdf
Reviewer 3 Report
It is a nice and important paper about the use of plants as proxy measurements for ambient air pollution of metals. Unfortunately there are a few issues which should be clarified. It needs major revisions.
1) I am aware that Milan may experience some significant air pollution, However, I think I did not really see some references which make it clear that Milan has a PM issue.
2) The authors use four sites which are close to each other. Why that close? Wouldn't it more reasonable to look into some sites, which are known to be exposed to specific sources and wouldn't it be better to systematically put these important bio-indicator measurements close to a routine air quality measurement site? It would be nice to see speciated PM routine measurements, but for instance routine CO measurements would already help, when looking into traffic sources. What about a more background site to see background conditions as a reference? I see that the authors mention a " not exposed plant" as a reference. What is the definition of "not exposed"? Where was its location? It seems the authors used sites with different altitudes above the surface. Unfortunately, they did not put plants at the surface and at a certain altitude above ground at the same site to address vertical profiles appropriately. If this is not done, discussion about altitude dependant results remain speculative.
3) Figure 1 should better show all the sites, unless there is a justification why one site (I guess it is the Department of the Biosciences. There is no description Fig. 4a in the figure caption. Figure 1 c is a bit surprising. Were the plants always located in front of the gate outside the air quality site? Figure 1d only shows a zoomed picture which shows a lot of background but the immediate environment. It sees there is a plastic wall to right side. What is that? Would this prevent free air flow? Figure 2 only shows a, b, c, d, but no information what site each letter stands for. L109-112: I do not see this plastic "cover" in Fig 1b. Also, I do not understand what the impact of cold are really would mean and whether excluding this natural phenomena would lead to a biased data set.
4) Results section:
L166-167: Is there a reason for this a bit surprising observation that only Cr and Zn were basically detected on the days 7, 30, 60, and 128, while Fig 4 actually shows that for instance Mn and Cu seems to show higher values on day 165 compared to Cr. Actually, Mn in Fig 4 is almost of the same magnitude as Zn in Fig 4, but Mn would show up at all for any earlier period, while Zn does.
L291-293: this may be true, but can leaching as a possible loss mechanism definitely excluded. It would be good, if the authors showed any rainfall, just in case.
5) Discussion:
I think L233-269 somehow contains introductory material and should be moved into the Introduction section.
L241: It is good to mention As, but it should be mentioned as well that this paper does not include As.
L251-253: this is certainly true that these species interact with plants, but what is the similarity with the metals? Do these gasphase compounds also accumulate in the plant? Do these compounds also enter the plants through the root? Some clarification would be helpful.
L277-278: If a compound is identified at trace level, this actually is not convincing to use this compound as unambiguous tracer for any source.
6) Fig. 6: unfortunately I have a problem with this figure. Based on the deviation bars for the Zn measurements in plant, I only see that those measurements are significantly different from each other, even in the periods for 7, 30 days. The authors definitely need to put deviation bars for the in-situ measurements in the PM data just to be fair and find out what the relationship among these different techniques would actually tell us. Also, I see that slope in the PM10 data is less from day 128 to day 165. I guess this would also actually mean that accumulation of PM in this period was less than before somehow coinciding with the trend in plant data. I am concerned that the authors (a) did not report any rainfall data or wind speed data and (b) report data at different altitudes. This all may make a difference, The authors only allude to this in L338-340, but did not try to look at least into some of these at least. I would assume that the ARPA site would have some meteorological data. Also, I understand than Zn might come from traffic and that Zn is a micronutrient for the plants. So why not include CO data from that site (if available) to verify the traffic origin. The advantage of including CO would also be that it would separate out wet deposition/removal processes due to rainfall from meteorological dilution and transport effects. I guess it would be worth a try.
7) some typos:
Replace "height" by "altitude" throughout the text (e.g. L 272)
Replace "at this purpose" by "for this purpose" (L275)
Replace "from many parameters" by "on many parameters" (L339)
Author Response
We thank the reviewer for his comments and suggestions. The answers are reported in the attached file.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors make some corrections but it is not enough for publication.
In the article, I still find "atomic emission spectroscopy".
The authors write "Analyses were carried out with an acceleration voltage of 5 kV, 10 kV e 15 kV and under high vacuum conditions", but from the EDX spectra can be easly seen that the analyses were made at 20 kV. Also, in the discussion and in conclusion sections authors do not mention the importance of these analyses (SEM and EDX) - why they choose to do this analyses.
Regarding the Figure 3, the authors must include an explanation why the content of Cr and Zn is higher in the plant which was not exposed than in some of the exposed plants.
The references list still have references which do not respect the format of the template.
Unfortunately, the authors must read again the article because it still need corrections. They must insert the novelty and the originality of the study.
Author Response
We have answered to the reviewer requires.
Author Response File: 
Author Response.docx
Reviewer 3 Report
The paper has largely improved. Still, some of my questions have not been fully addressed. Here I just repeat my initial questions followed by my inquiries:
2)
- a) What about a more background site to see background conditions as a reference? I see that the authors mention a " not exposed plant" as a reference. What is the definition of "not exposed"? Where was its location?
[Follow-up inquiry]
The authors state: "...the plant was kept in an indoor environment (in particular in a
room inside the university not exposed to any internal pollution source)." The authors may want to clarify what that environment. Usually, indoor pollution is not negligible.
- b) It seems the authors used sites with different altitudes above the surface. Unfortunately, they did not put plants at the surface and at a certain altitude above ground at the same site to address vertical profiles appropriately. If this is not done, discussion about altitude dependant results remain speculative.
[Follow-up inquiry]
I understand all the limitations of that project. However, bearing in mind those limitations it is still not a valid approach to compare surface measurements with measurements at a certain altitude above the ground taken at a different site. It remains speculative and should be indicated as such.
6)
- a) Fig. 6: unfortunately I have a problem with this figure. Based on the deviation bars for the Zn measurements in plant, I only see that those measurements are significantly different from each other, even in the periods for 7, 30 days. The authors definitely need to put deviation bars for the in-situ measurements in the PM data just to be fair and find out what the relationship among these different techniques would actually tell us.
[Follow-up inquiry]
Even, if accumulative data is shown this data has measurement uncertainties which should be shown.
- b) Also, I see that slope in the PM10 data is less from day 128 to day 165. I guess this would also actually mean that accumulation of PM in this period was less than before somehow coinciding with the trend in plant data. I am concerned that the authors (a) did not report any rainfall data or wind speed data and (b) report data at different altitudes. This all may make a difference, The authors only allude to this in L338-340, but did not try to look at least into some of these at least. I would assume that the ARPA site would have some meteorological data.
[Follow-up inquiry]
The authors' reply is certainly not correct, as micrometeorological conditions critically depend on the altitude above the ground, as does deposition.
Comments for author File: Comments.pdf
Author Response
All the answers to this reviewer were already present in our previous revised version.
