Comparison of the Concentrations of Heavy Metals in PM2.5 Analyzed in Three Different Global Research Institutions Using X-ray Fluorescence
, Andrea McWilliams 3, Choong-Min Kang 4, Simon Kim 5 and Sungroul Kim 1,2,*Round 1
Reviewer 1 Report
Dear authors
I like the idea of your study, it is always good to check the reproducibility of results of every technique especial on XRF results since it is a technique widely used. Nevertheless, it is not very clear to me the reason why you didn’t apply this study on reference samples. As you describe the PM2.5 filters exhibited a heterogeneous distribution of metals on their surface and the area of minimum representative area of analysis wasn’t explored. This part is a weakness in the production of results from each laboratory. From another point of view, I understand that you wanted to check the reproducibility of the results on real samples, cases so the study is interesting.
Comments for author File: 
Comments.pdf
Author Response
Original Manuscript ID: applsci-1664112
Original Article Title: “Comparison of the Concentrations of Heavy Metals in PM2.5 Analyzed in Three Different Global Research Institutions Using X-ray Fluorescence.”
References
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- Health and Safety Executive(HSE), Cadmium and you Working with cadmium: Are you at risk? In England, 2011; p https://www.hse.gov.uk/pubns/indg391.pdf.
- Yang, A.-M.; Lo, K.; Zheng, T.-Z.; Yang, J.-L.; Bai, Y.-N.; Feng, Y.-Q.; Cheng, N.; Liu, S.-M., Environmental heavy metals and cardiovascular diseases: Status and future direction. Chronic Diseases and Translational Medicine 2020, 6, (4), 251-259.
- health and Safety Executive(HSE), Nickel and you Working with nickel – are you at risk? In The Control of Substances Hazardous to Health (COSHH) Regulations, England, 2013; p https://www.hse.gov.uk/pubns/indg351.pdf.
- Niu, J.; Liberda, E. N.; Qu, S.; Guo, X.; Li, X.; Zhang, J.; Meng, J.; Yan, B.; Li, N.; Zhong, M.; Ito, K.; Wildman, R.; Liu, H.; Chen, L. C.; Qu, Q., The role of metal components in the cardiovascular effects of PM2.5. PLoS One 2013, 8, (12), e83782.
- Liang, R.; Yin, P.; Wang, L.; Li, Y.; Liu, J.; Liu, Y.; You, J.; Qi, J.; Zhou, M., Acute effect of fine particulate matters on daily cardiovascular disease mortality in seven cities of China. Zhonghua liu xing bing xue za zhi= Zhonghua liuxingbingxue zazhi 2017, 38, (3), 283-289.
- Olesik, J. W., ICP-OES Capabilities, Developments, Limitations, and Any Potential Challengers? In 2020; pp https://www.spectroscopyonline.com/view/icp-oes-capabilities-developments-limitations-and-any-potential-challengers.
- Portable Analytical Solutions(PAS), Taking It To The Limit: An Essential Guide To XRF Detection Limits. In Copacabana, 2022; pp https://www.portableas.com/news/xrf-detection-limits-guide/.
- Rasmussen, P. E.; Dugandzic, R.; Hassan, N.; Murimboh, J.; Gregoire, D. C., Challenges in quantifying airborne metal concentrations in residential environments. Canadian Journal of Analytical Sciences and Spectroscopy 2006, 51, (1), 1-8.
To: Applied Sciences Editor
Re: Response to reviewers
Dear Editor,
Thank you for allowing us to re-submit our manuscript with the opportunity to address the comments of the reviewers. We are uploading our point-by-point response to the comments and an updated manuscript with yellow highlighting indicating changes.
Best wishes,
Kim et al.
Reviewer#1, Concern # 1: Abstract Very well described, I have no comments
Author response: Thank you for your comment
Reviewer#1, Concern # 2: Introduction: A general comment: you write a lot about the effects of PM2.5 in health but in a vague way, it would be more interesting to put some numbers, what I mean is that is the presence of PM2.5 responsible for all these diseases? Is there a limit that above that, the presence PM2.5 or specific metals in them can cause bad effects in health? This is also related with the detection limits of the techniques, XRF and ICP detection limits should be included. Then what is really missing in the introduction is other comparative studies for the analysis of PMs.
Author response: Thank you for your valuable comment.
Author action: We updated the manuscript by showing the heavy metal exposure limits in air, and reference concentrations for airborne metals. PM2.5 includes a number of harmful substances, including heavy metals and organic compounds [3]. NAAQS(National Ambient Air Quality Standards) and USEPA(United States Environmental Protection Agency) have set limit value in ambient air for heavy metals like lead(0.15 μg/m3). And According to Integrated Risk Information System (IRIS) on Cadmium, National Center for Environmental Assessment (Washington, DC, U.S.A) 0.2 ng/m3 of cadmium [4] and 12 ng/m3 of chromium [10] as their higher concentration in ambient air may cause respiratory and circulatory problems besides systemic (extra-pulmonary) effects such as bronchial and pulmonary irritation as well as increased frequency of kidney stone formation[1]. In addition, higher concentration in chromium ambient air causes ulcerations of the septum, bronchitis and decreased pulmonary function[2].
Beside that our introduction of the original manuscript already mentioned the health effect of metals as well as PM2.5 and its margin of exposuire.(Line 40-46)
We already have provided detection limit of ICP and XRF on our previous original manuscript and the results of comparative study in our manuscrip. (Line 99-103)
Please see below for details
Reviewer#1, Concern # 3: Lines 40-42: In which amounts these metals can cause problems?
Author response: Thank you for your valuable comment
Author action: We updated the manuscript by including the exposure limits in which above that, the detrimental effects on human health may arise.
Reviewer#1, Concern # 4: Lines 44-79: I like that you put some many studies on the hazardous effects of the PMs on health but maybe it is too much since your paper is not about the effects. Again I would like to have some concentrations on the metals that cause the effects.
Author response: Thank you for your comment
Author action: We updated the manuscript by highlighting the detrimental health effects of heavy metals found in PM2.5 in humans. Also the occupational exposure limit for lead in air set out in the Regulations is 0.15 μg /m3 and the limit above that level have shown to affect blood which may lead to anemia, affect the nervous system and kidney as well as infertility in males[1]. cadmium being carcinogenic in humans, exposure limit is measured over a 15-minute period and has been set at 0.05 mg/m3 of air[2]. In addition, the exposure to elements like As, Cd, Hg, and Pb is statistically associated with cardiovascular diseases[3].
Nickel exposure limit was set at 0.5 mg/m3 averaged over an 8-hour period [4] and it’s exposure above the accepted level has shown significant effect on heart rate variability[5], and increased concentrations of nickel, zinc, and lead have been reported to be associated with an increase in emergency department(ED) visits for cerebral hemorrhage in China [6].
Reviewer#1, Concern # 5: Lines 87-88: Maybe in this sentence you should address the concentration of the individual elements that might be harmful. The way it is written implies that just their presence can cause cancer.
Author response: Thank you for your insight.
Author action: We updated the manuscript by focusing more on effects of heavy metals on health
Reviewer#1, Concern # 6: Line 92: ICP has a lower detection limit, please write the detection limits for example a few ppm are detectable in XRF, what about ICP?
Author response: Thank you for your comment We mentioned the detection limit for ICP and XRF in the main text. Although ICP has a lower detection limit which ranges from <1 ppm to >100 ppm[7] and XRF detection limits for most elements are 2-20 ng/cm2 for micro samples, thin samples, aerosols, and liquids[8], both XRF and ICP devices have comparable element detection capacities, with lower measurement error, and hence, similar accuracy
Author action: We updated the manuscript by including the detection limits for ICP and XRF
Reviewer#1, Concern # 7: Line 93-94: similar accuracy, I think that ICP is more accurate again; you should specify the accuracy of each technique.
Author response: Thank you for your comment. The authors meant that despite some differences, both techniques can provide excellent results even if ICP’s accuracy is better. Both techniques are capable of giving excellent accuracy and precision but the systematic errors are much easier to eliminate and the random measurement error can be as low as 0.5 % for ICP [37].
Author action: We updated the manuscript by highlighting the accuracy of ICP in the main text
Reviewer#1, Concern #8: Line 106: Low concentration samples, all PMs have low concentrations, please specify
Author response: Thank you for your comment. The authors clarified that the previous study with PM Concentration as low as ≤ 1.3 ng/m3, elements such as Cr, As, Ni, and Sr exhibited high DL-passing rates (from 92% to 100%) for ICP-MS
Author action: We updated the manuscript by clarifying the PM concentration samples in the main text.
Reviewer#1, Concern #9: Line111: certain level, please specify the level
Author response: Thank you for your comment. As seen in a preliminary home air study in Ottawa, low sample mass is a major barrier in obtaining valid and reliable elemental data because many metals are below the detection limits for not only Energy Dispersive X-ray Fluorescence spectrometer but also for ICP-MS[9] therefore the 0.06 mg minimum cut-off for particle mass ensures reliable analysis results for most elements using ICP-MS.
Author action: We updated the manuscript by
Reviewer#1, Concern #10: XRF analysis: Table1: This table is not necessary, you should exclude it.
Author response: Thank you for your valuable comment
Author action: We updated the manuscript using a periodic table of elements and color coding elements detected by each institute.
Reviewer#1, Concern #11: Figure 2: The resolution of the image should be improved.
Author response: Thank you for your comment
Author action: We updated the manuscript by improving the resolution of the image
Reviewer#1, Concern #12: Page 6: Please include the description of the spectrometers and the measurement conditions, at this point you should write the area of analysis at each spectrometer.
Author response: Thank you for your comment. The institute#1 used EDXRF (Epsilon 4, Malvern PANalytical Malvern Panalytical) the new high-performance benchtop analytical tool for the determination of the chemical composition of all kinds of material. It gives fast results and low detection limits through the whole analytical range. It is also calibrated using reference materials that match the composition of the routine sample.
The Institute #2 used Thermo ARL Quant’X EDXRF for analysis. Thermo ARL Quant’X EDXRF. The Thermo Scientific™ ARL™ QUANT'X EDXRF Spectrometer provides high-volume, low-volume and trace element quantification for a wide range of samples including bulk solids, granules, powders, thin films and liquids. This complete benchtop Energy Dispersive X-Ray Fluorescence (EDXRF) system with standardless software and accessories is ideal for central and contract laboratories, as well as environmental monitoring, chemical, mining, forensic, food, cement and metal industries. Ideal for elemental analysis.
INSTITUTE#3 conducted analysis using Epsilon 5 EDXRF spectrometer. The Epsilon 5 EDXRF spectrometer provides easy sample preparation, rapid sample throughput and Epsilon 5 EDXRF spectrometer is capable of the required detection limits which is an important factor for the analysis.
Author action: Authors described the spectrometers for each institute that analyzed PM2.5 samples.
Reviewer#1, Concern #13: Line 217: Figure 2, please change to figure 3
Author response: Thank you for your insight
Author action: We updated the manuscript by replacing Figure 2 by Figure 3 in line 217
Reviewer#1, Concern #14: Table 2: LOD of Ni is 0.06ppm, maybe this is a mistake; perhaps 0.6ppm is the correct number.
Author response: Thank you for your comment
Author action: We updated the manuscript by correcting the typo
Reviewer#1, Concern #15: Discussion
Lines 285-293: This is not very clear to me, you compare PM concentrations from the same area but from different time period, why? Even if it was different (like a lot) it would still mean nothing.
Author response: Thank you for your comment. Because we collected our PM and metal samples from Korean residential areas, we compared the levels of them to those results reported from China in 2020. There were relatively a large number of papers containing metal concentration based on air but studies reporting the concentration based PM2.5 mass (Metal/PM2.5 mass) were rare. Therefore, we used the Chinese studies just for comparison purpose, although we also knew that the study period was different between Korean and Chinese studies.
Reviewer#1, Concern #16: Lines308: In our future study we may conduct comparison using certificate samples, I think this test should be done firstly
Author response: Thank you for your comment
Author action: In this study, our study purpose was comparison analysis results of the same samples among 3 different institute. We considered those large number of samples showing various concentration levels field study. We deleted the sentence “conducting comparison using certificate samples” to avoid unnecessary misunderstanding.
Reviewer#1, Concern #17: Conclusions
Line 317: You should specify the minimum representative area of the samples and compare with the one that was analyzed.
Author response: Thank you for your comment
Author action: We clarified our conclusion by removing those unnecessary sentences.
Reviewer 2 Report
Dear authors,
in principle a good made comparison. A few remarks:
"Results showed the detection rates of most heavy metals across the three institutions (n = 25 metals) to be approximately 90%."
Please define clearly what you mean with detection rate.
But for me the key sentence is:
"PM2.5 shows an heterogeneous distribution on filter used in this study as anticipated. Results of XRF confirm the inhomogeneity of PM2.5 distributions and the need of a wider irradiated area for a better representativeness of the total elemental mass deposition."
This is a point that is not sufficiently discussed in the paper. For example, you do not mention the beam sizes for the different instruments. It is possible that the differences are just due to different parts of the samples, and therefore you ended up measuring different samples. Please address this aspect. If possible make a scan with (micro?) XRF and quantify the uncertainty which you expect due to the inhomogenity.
Table 1 could be better a graphic. Maybe just a periodic table where you color code which elements have been seen from which institute.
Good luck
Author Response
Original Manuscript ID: applsci-1664112
Original Article Title: “Comparison of the Concentrations of Heavy Metals in PM2.5 Analyzed in Three Different Global Research Institutions Using X-ray Fluorescence.”
To: Applied Sciences Editor
Re: Response to reviewers
Dear Editor,
Thank you for allowing us to re-submit our manuscript with the opportunity to address the comments of the reviewers. We are uploading our point-by-point response to the comments and an updated manuscript with yellow highlighting indicating changes.
Best wishes,
Reviewer#2, Concern #1: In principle a good made comparison. A few remarks:
"Results showed the detection rates of heavy metals across the three institutions (n = 25 metals) to be approximately 90%."Please define clearly what you mean with detection rate.
Author response: Thank you for your comment. Here is our definition for the detection rate, (# of samples showing metal larger than LOD divided by entire samples numbers i.e., 25). We put this definition on the main text as well as corresponding table as remarks. (Line 222)
Reviewer#2, Concern #2: But for me the key sentence is:
"PM2.5 shows a heterogeneous distribution on filter used in this study as anticipated. Results of XRF confirm the inhomogeneity of PM2.5 distributions and the need of a wider irradiated area for a better representativeness of the total elemental mass deposition."
This is a point that is not sufficiently discussed in the paper. For example, you do not mention the beam sizes for the different instruments. It is possible that the differences are just due to different parts of the samples, and therefore you ended up measuring different samples. Please address this aspect. If possible, make a scan with (micro?) XRF and quantify the uncertainty which you expect due to the inhomogeneity.
Author response: Thank you for your comment
Author action: We removed that unclear sentence to make it more understandable and avoid confusion.
Reviewer#2, Concern #3: Table 1 could be better a graphic. Maybe just a periodic table where you color code which elements have been seen from which institute.
Author response: Thank you for your important comment
Author action: We updated the manuscript by color coding a periodic table according to elements detected by each institute
Round 2
Reviewer 2 Report
Good luck!
