Laser-Induced Breakdown Spectroscopy Detection of Heavy Metal Contamination in Soil Samples from North Birmingham, Alabama
and Sergey Mirov 1,2
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis paper explores the application of Laser-Induced Breakdown Spectroscopy (LIBS) technology in detecting heavy metal contamination in soil samples from the North Birmingham area of Alabama. The research team collected 60 soil samples from Superfund sites and control areas and systematically analyzed them using LIBS technology. The study found that LIBS effectively detected arsenic (As), lead (Pb), and manganese (Mn) in the affected area's soil samples, with detection limits of 16 ppm for lead, 43 ppm for arsenic, and 33 ppm for manganese. The results were compared to ICP-MS measurements, showing a good linear relationship and correlation. The need for major revisions stems from a number of issues that include the need for clarification on certain methodological choices, a more comprehensive analysis of the results, and additional details to ensure the reproducibility and robustness of the study. The specific comments are as follows:
1. Can you elaborate on the strategy and methods used for sample collection, including the representativeness of the samples and any contamination control measures during collection?
2. The manuscript mentions a comparison between LIBS results and ICP-MS measurements but does not provide specific comparative data or charts. Could you include more comparative data to demonstrate the accuracy of the LIBS technique?
3. The paper mentions the use of argon gas to purge the LIBS system chamber at atmospheric pressure to improve detection sensitivity. Could you describe in detail how this process affects signal intensity and detection limits?
4. Soil samples can have significant variations in their physical and chemical properties. How does this heterogeneity affect the results of LIBS analysis, and what steps were taken to address this issue?
5. The calibration curves reportedly show good linearity at low concentrations but saturation at higher concentrations. Could you provide the full linear range of the calibration curves and discuss how this range can be extended?
6. Could you provide a detailed explanation of how the Limits of Detection (LoD) were determined and discuss their relevance to EPA standards?
7. The paper mentions the volume of the LIBS system chamber and argon gas flow rate but does not discuss the control of temperature and humidity. How do these environmental factors influence the experimental results, and what measures were taken to control these conditions?
8. Did the study consider the effects of different soil types on LIBS analysis? Could you discuss the generalizability of the results and provide validation data across different soil types?
9. The paper refers to correlation coefficients but does not mention other statistical analysis methods. Could you provide more information on data distribution, outlier handling, and statistical significance?
10. The manuscript mentions the optimization of LIBS technology but lacks details on the specific technical improvements made. Could you describe these optimization measures and their impact on the results?
11. What are the environmental and public health implications of the study's findings? Could you provide a risk assessment based on the LIBS results and suggest potential mitigation measures?
Author Response
I have uploaded the point-by-point response to the reviewer's comments in a Word file. Please find the attached file. Thank you.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe paper submitted by Adhikari et al. is a rather straightforward application of Laser-Induced Breakdown Spectroscopy (LIBS) to the analysis of polluted soil. The authors use a linear univariate approach, which is clearly inadequate for the analysis of Mn, which is measured using different experimental conditions with respect to As and Pb. Better results could have been probably obtained using a non-linear multivariate method. In any case, the manuscript is potentially interesting, although the conclusions do not seem to be fully coherent with the data presented.
The weak point of the manuscript is the use of an outdated expression for the Limit of Detection (the IUPAC formula in eq. (1)), which typically seriously underestimates the LOD when few reference samples are used in the calibration curve, as in the case presented (5 points for As and Pb, 3 points for Mn). Eq. (1) has been criticized many years ago by Long and Winefordner (“Limit of Detection. A closer look at the IUPAC definition”. Anal Chem 55, 712A-724A (1983)) and recently reconsidered by the same institution (see Poggialini, F. et al. “Calculating the Limits of Detection in Laser-Induced Breakdown Spectroscopy: Not as Easy as It Might Seem”. Applied Sciences 2023, Vol. 13, Page 3642 13, 3642 (2023)).
The LODs must be recalculated using the correct formula, and the conclusions rewritten accordingly.
Before resubmitting the updated manuscript, the authors should also correct the sentence “Argon promotes larger and more stable plasma emissions while reducing self-absorption, resulting in a more uniform plasma core temperature [24]”. In ref. [24] is clearly written that Argon, by improving the plasma homogeneity, reduces the self-reversal effect, not the self-absorption. A homogeneous plasma could still show considerable self-absorption without showing signs of self-reversal.
Author Response
I have uploaded the point-by-point response to the reviewer's comments in a Word file. Please find the attached file. Thank you.
Sincerely,
Nirmala
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsIn the following manuscript, “Laser-Induced Breakdown Spectroscopy Detection of Heavy Metal 2
Contamination in Soil Samples from North Birmingham, Alabama” the author identified and analyzed heavy metals in soil samples collected from Superfund sites in North Birmingham, Alabama, specifically in affected areas with Zip codes 35207, 35217, and control area 35214.. The author should explain the following comments.
1. Please comment on resolution of the spectrometer
2. How the energy of the laser was optimized?
3. Please explain about the physical explanation of signal enfacement in the presence of argon environment?
4. Please label the other spectral lines present in the spectra of Fig. 3 (a-c).
5. How the spectral lines of the As, Pb, and Mn were identified?
6. The author should include the complete spectra in the results section.
7. The author need to highlight the novelty in introduction in detail.
Comments on the Quality of English LanguageMinor editing of English language required.
Author Response
I have uploaded the point-by-point response to the reviewer's comments in a Word file. Please find the attached file. Thank you.
Sincerely,
Nirmala
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have addressed the previous comments.
Author Response
Dear Reviewer,
Thank you for your valuable comments and suggestions. We appreciate the time and effort you put into reviewing our manuscript. Your input is highly valued.
Sincerely,
Nirmala Adhikari
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have replied satisfactorily to all the concerns I expressed in my first review. The manuscript should be published in present form without any further modification.
Author Response
Dear Sir/Ma'am,
We appreciate your comment. I have attached a detailed response to your comments in a Word file. Please check the attached file. Thank you.
Sincerely,
Nirmala
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe author didn't incorporated answers to my questions. Commets are attached again.
In the following manuscript, “Laser-Induced Breakdown Spectroscopy Detection of Heavy Metal 2
Contamination in Soil Samples from North Birmingham, Alabama” the author identified and analyzed heavy metals in soil samples collected from Superfund sites in North Birmingham, Alabama, specifically in affected areas with Zip codes 35207, 35217, and control area 35214.. The author should explain the following comments.
1. Please comment on resolution of the spectrometer
2. How the energy of the laser was optimized?
3. Please explain about the physical explanation of signal enfacement in the presence of argon environment?
4. Please label the other spectral lines present in the spectra of Fig. 3 (a-c).
5. How the spectral lines of the As, Pb, and Mn were identified?
6. The author should include the complete spectra in the results section.
7. The author need to highlight the novelty in introduction in detail.
Author Response
Dear Sir/Ma'am,
We appreciate your comment. I have attached a detailed response to your comments in a Word file. Please check the attached file. Thank you.
Sincerely,
Nirmala
Author Response File: Author Response.pdf
Round 3
Reviewer 3 Report
Comments and Suggestions for AuthorsAll comments have been incorporated. I accept manuscript for publication in present form.
Author Response
Dear Reviewer,
Thank you for your valuable comments and suggestions. We appreciate the time and effort you put into reviewing our manuscript. Your input is highly valued.
Sincerely,
Nirmala Adhikari
