Iron and Molybdenum Isotope Application for Tracing Industrial Contamination in a Highly Polluted River
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsInteresting research. The authors should conduct a thorough literature review of isotopic tracing of contamination. Several papers have been published in the tracong of groundwater. Perhaps also for rivers other research has been carried out. Please make sure you cite them all and you explicitly state if and to what extent your Fe/Mo isotopic approach is innovative.
Title: I suggest to reformulate as “Iron and molybdenum isotopic ratios trace industrial contamination in a highly polluted river”
Abstract
The first 3 sentences are not in logical order. The second sentence should come as third, such as. “
Rivers adjacent to industrial zones usually suffer FROM severe pollution. industrial wastewater that has undergone sewage treatment processes may be legally discharged into rivers under water quality permits Previous studies have frequently employed isotopic tracers to identify potential contaminants for pollution control. …”
Introduction
Please reformulate sentence “However, risk assessment by monitoring the quality of water resources is not enough for global sustainable development nowa-days; the source identification seems to be critical in controlling the release of pollutants into the natural environment.” and provide detail to explain the motivation for conducting this study.
In Lines 35-37: please reformulate. Isotopic signature is not “important” because of “inputs”. You are trying to say that pollution source tracing through isotopic ratios is an increasingly relevant option because of the need to differentiate urban from industrial effluents.
Please reformulate sentence in Lines 42-45 because it is not understandable.
In Line 66, “nature of water bodies” sounds very ambiguous. Please use different expression (presence of altered Mo isotopic ratio?)
Line 71, please never start a sentence using “However”.
In 72, not clear if “material transferring/removing processes” implies something specific or generic. You could perhaps call it “biogeochemical processes” or “biogeochemical exchange/recombination”.
Text in Lines 83.91 should be moved to 2.1 Study area. It should be clear that the objective of this research is broadly relevant and not only specifically relevant for the study site in question.
Sentence in Lines 91-94 provides a wrong representation of study aims (correlation between pollutants and wastewater) and mixes aims and methods (by analysing…). Analysis is a method and not a study aim. The whole sentence should be deleted.
Study aims are correctly represented by sentence starting in 94 “Through this study…” where “understanding source contributions” (but “source tracing” could be better) is the correct objective. “To minimise impact…” is the correct overall aim. “ To achieve the goal of sustainable development” is unnecessary and should be deleted.
After Line 97, please add further clarification to explain why it is relevant to identify pollution sources using isotopic ratios, what are the specific advantages and expected challenges in using this approach, and provide further detail to explicitly state the motivation that induced you to carry out this research.
I would also recommend, at this point, to provide one or more falsifiable hypotheses that could be directly linked each to a method and to its results. This would provide a strong and explicit “line of evidence” that would highlight the specific original contribution of this research.
Sample collection
Please indicate the dates of sampling and state whether it was a rainy period or not to underline if you were sampling baseflow, which would have a higher proportion of effluent discharge, or high discharge flow that would be significantly influenced by rainfall.
Please explain how were samples collected instead of inviting the reader to consult protocol (NIEA W104) of Environmental Protection Administration (EPA) of Taiwan.
Line 122: what is a “time-series” water sampling exactly? Please provide detail.
It is not expected that Tables containing results should be called in a paragraph addressing Methods. I recommend that all results are treated in the Results section.
In the text, it is mentioned that samples were taken in 3 types of waterbody: the effluent of several industries, the Agongdjan River, the tributary flowing from the Industrial Park towards the Agongdjan River. However, this is not what appears in Table 1, where only industrial effluents and the Agongdjan River concentrations are shown. It is not clear where were these samples taken.
2.3.1. and 2.3.2. These methods are highly relevant. I am not en expert, but I am wondering if you could add detail to specify that checks are carried out to verify that no Fe and Mo are lost during rinsing.
The methods section starting in 2.3 should be introduced highlighting the principles of the methodology used before providing the detail (as in 2.3.1, 2.3.2., etc.).
In Lines 184-185, please add the detail of the 4 Fe isotopes measured.
In Lines 244-248, it seems to me that this discussion could provide a falsification of hypothesis 1: Fe isotopic ratio can be used to trace pollution, but it does not falsify hypothesis 2: Mo isotopic ratio can be used to trace pollution. Please provide details regarding statistical significance.
Please delete or reformulate sentence in Lines 260-261 because it cannot be understood what is meant here.
It is not clear why Figure 2 comes before Figure 3. I would suggest to reverse this order-
I am not a fan of mixing Results and Discussion. However, if this is done, there should be some order in the presentation of paragraphs, with Results coming first and discussion later.
Please provide evidence of a lack of correlation between rainfall and Fe in river water. It is expected that particulate Fe would vary together with sediment and it should be expected that sediment would vary with rainfall, i.e. with river discharge.
The sub-paragraph in 224-231 is highly surprising. It is not clear why you comment (again) on the partial success of water treatment, as this was not the objective of you study. Secondly, it is not clear what was observed “in the nature system”. All this needs to be reformulated to become understandable.
Please reformulate text in Lines 277-281. It cannot be understood that a connection exists because levels on pollution in the effluents are high. Please rewrite to explain what this means.
In Line 292, please explain why would one expect to observe a correlation with precipitation.
It is highly surprising that Sr concentrations presented in Table 2 are considered “relatively stable”. In reality Sr concentrations fluctuated from 176 to 853 ppb. Please explain.
What is “significant” rainfall? In Lines 294-296 you make a conclusion on the basis of very little data on a point that is not directly connected to your research objectives. No statistical significance can be claimed. Please reformulate as a hypothesis, or delete.
In 299 “monitoring stations”? Are these on the river? These were not shown on Figure 1, where are they?
In 300, what “monitoring site” are you referring to? The monitoring site in Figure 1 is not on the River but on a tributary. Are these values from river samples or from tributary samples? Please explain.
Reasoning in 304 up to 314 would be best supported if a clear hypotheses (1. pollution by treated effluent, and 2. pollution by direct industrial discharge) was explicitly stated, and if it could be disproved by a testing procedure. If the data presented here is insufficient and it does not allow this, it could be stated what further evidence would be necessary to disprove it.
3.3. Application of stable isotopes in contamination investigation could be better phrased as “3.3. Fe & Mo stable isotopes as tracers”
Line 319 Please reformulate sentence “As a river located in close proximity to the Kangshan Benjhou Industrial Park, the most straight forward target for the discharging of industrial wastewater is dumping into nearby Agongdian River.”
Paragraph 319-326 is a sort of introduction to the relevance of industrial pollutiojn and it does not fit in the Discussion, in a section that should address “application of stable isotopes…” Please delete it.
Please use “Fe and Mo isotopic ratios” instead of “Fe and Mo isotopic compositions”
In 339, please use “isotopic ratios” instead of “isotopic values”
In Lines 341-341, it is not clear how this information is integrated in the reasoning to detect pollution sources, i.e.: whether it is pollution by raw or by treated industrial sewage.
The expressions “output industrial wastewater” and “primary industrial wastewater” are not explicitly clear. Please use “treated industrial effluent” and “raw untreated industrial effluent” to avoid any confusion.
In Line 368, please reformulate sentence “It is speculated that specific entities may have attempted to dilute the sig-368nals of primary wastewater in the river, which should not be present, by taking advantage 369of natural precipitation events” as it cannot be understood.
The Conclusion should explicitly state whether isotopic tracing of contamination has been attempted before in similar studies, or if this is a first study of this kind.
Please note that isotopic tracing of contamination has been applied to groundwater. Please see “Michael Lawson (2011) Isotopic Tracers of Groundwater Contamination: Techniques, applications and considerations EPA Hydraulic Fracturing Study Technical Workshop on Chemical and Analytical Methods 24 – 25th February 2011 Arlington, Virginia. Can be Downloaded from https://www.epa.gov/sites/default/files/documents/isotopictracingofgroundwaterccntamination.pdf
In this report, Sr isotopes were used for tracing contamination. Please explain why have you not used Sr isotopes in your study.
Please see Sankoh et al. 2022 Water 2022, 14(1), 35; https://doi.org/10.3390/w14010035
Please see Kong et al. 2018 https://doi.org/10.1016/j.scitotenv.2018.05.034
Additional comments have been added to the attached file as Comments
Comments for author File: 
Comments.pdf
Although grammatical errors are few, the text needs to undergo a thorough revision by an English scientific editor. Several sentences are very obscure. In places the text is not relevant (it does not fit the content of the heading). Sometimes, the text sounds redundant. The authors choose not to seprate Results and Discussion; I would recommend to go back to a more traditional framing with explicit hypotheses linked to methods, then results, then a discussion to highlight a clear line of evidence in the authors' reasoning.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsA very interesting and very sound study. I would point out two very minor issues:
1. In Table 1, the authors mention at line 207 a list of metal data in Table 1, including Nd. However, there is no Nd data in Table 1. Authors should either include the Nd data, remove Nd from the list of metals at line 207, or include a statement as to why Nd was in the reference but not included here.
2. In Figure 2, both 2a and 2b, while lines of best fit are either inappropriate (2a) or tenuous (2b), there are definite patterns visible in both 2a and 2b for the Cu, Fe, and Pb data points. It is interesting that the patterns of the data points are very similar in shape, given the different metals, and their common shapes might point to something significant about the data itself or shed light on another part of the investigation. I don't think authors need to comment on that in this paper, but I certainly found it intriguing.
Comments on the Quality of English LanguageThe English of the submission is really quite good. There are a few issues with agreements here and there (single vs. multiple subject-verb agreement), but it reads very well to a native English speaker.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsIndustrial waste water pollutes river and lake, ocean, land environments, and harm the health of human being. Waste water must be treated before discharging. So, how to monitor the characteristics of discharged waste water is an important work. Isotope can trace the sources in the past researches. Non-traditional stable isotopes maybe are good indictors also.
Questions and suggestions:
1. Fe and Mo are heavy elements, there are a little isotope fractionation. Authors must testify there are an obvious isotope fractionation. But from the results of this MS, it is different to reflect this. And there is no point to compare with different elements, we do not what’s relationship among them, and these element geochemical actions. So, it is best to explain the isotope fractionation.
2. It is best to add Table 1 and table 2.
3. In the Figure 2, [E]/[E]* must be described clearly. And, why are ratios of different elements used to setup relationship lines? And why “As shown in this study, the variation of Mo isotopes between treated and untreated sewages (△98/95Mo, Figure 2b) is more indicative of the purification level of metal content in industrial wastewater compared to the variation of Fe isotopes (△56/54Fe, Figure 2a).”?
4. We do not know how about the information of collecting water samples, and the methods to treat industrial wastewater. So, it is difficult to judge what’s means about the results of Figure 2. It is difficult to prove whether or not there are relationship between treated and untreated wastewater for Fe and Mo concentration and isotopes. What is the methods of treating industrial wastewater?
5. Suggest to introduce the setting information of river catchments, especially, the basement rock information.
6. “In contrast to the aforementioned elements, the concentration fluctuations of Sr and Mo appear to be correlated with precipitation.”, whether, are the Mo and Fe isotopes in the wastewaters impacted by the sources of surface land along the catchments, and much heavier for Mo isotope?
7. It is difficult to reflect the signals of waste water contamination in the Figure 5.
8. From the figure 4, it is clear that different sites, the Fe isotopes are different. That means, Fe isotopes are controlled by the different nature rocks, not by the isotope fractionation. It is the same as Mo isotope also.
Comments on the Quality of English LanguageNo
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThank you for giving me the chance to review this study. Some major flaws exist in the research approach and the results reported in the current manuscript version. Therefore, I would like to recommend this manuscript be returned to the authors for major revisions, as suggested below, before publication in the journal
Line 35-36: Clarify the connection between the application of isotopic composition and its significance in tracking pollutant sources.
Line 88: Provide more precise and up-to-date statistics, especially regarding the pollution levels in 2022, to enhance accuracy.
Line 116: Ensure consistency in terminology, for example, using "sewage" in one instance and "wastewater" in another.
Line 121: Provide a brief explanation or context for the suggested protocol (NIEA W104) to enhance understanding.
Line 217-230: If applicable, briefly explain the statistical significance of the isotopic variations between different industries and before/after sewage treatment.
Line 217-230: Elaborate on the observed isotopic differences between primary and output wastewater and relate it to the material removal process mentioned in the study.
Line 218-219: Clearly specify the units used for δ56/54Fe and δ98/95Mo values for better understanding.
Line 367-368: Elaborate on the connection between specific rainfall events and the speculated attempts to dilute primary wastewater signals.
Comments on the Quality of English Language
Minor editing is needed.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 5 Report
Comments and Suggestions for AuthorsYu-Hsuan Liang, Po-Chao Wu, Shail Vijeta Ekka, Kuo-Fang Huang, Der-Chuen Lee.
Iron and molybdenum isotope application for tracing sources of contamination in highly polluted river
The study carried out by the authors is relevant because it is aimed at assessing the possibility of using iron and molybdenum isotopes for the quantitative identification of wastewater in surface waters.
At the same time, the results obtained, in my opinion, require clearer statistical confirmation. In particular:
Lines 307-308
The authors write: In contrast to treated wastewater (Figure 2), Fe isotopic composition shows a positive correlation with concentrations of Cr, Fe, Cu, and Pb (Figure 4).
The authors used R2 as the only indicator to test the correlation, and the correlation was considered positive when R2=0.35–0.5. In my opinion, other metrics such as sig value should be added to illustrate the accuracy of the match.
Conclusion
Please use the conclusions to summarize the main findings and discuss their scientific and/or practical significance. Were the objectives of the study achieved? What uncertainties and unresolved issues remain? What might future research directions be? These are questions that should be answered in the conclusion.
Minor
Fig. 1
It is necessary to indicate the left figure (for example, the island of Taiwan), add a sub-figure with the location of the suspected sources of pollution and sampling points for all samples indicated in Tables 1 and 2.
Tables 1 and 2
It is necessary to indicate the coordinates of the samples taken.
Comments for author File: Comments.pdf
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThis revised version represents a significant improvement. The text is fully understandable but minor language issues persist. The title could be improved by using a different expression instead of "application" or "applications" (the second one is worse).
There is a partial redundancy in the treatment of concentration dilution of river discharge increase. Please try to avoid repetition.
There is apparent increase in metal concentration during heavy rains. It appears that industrial pollution sources are being mobilised by rain events, or industrial effluents overcome treatment because of high river discharge (is., water treatment cannot cope with increased effluent volume). I suggest adding a brief comment about this within the main text that would serve as further clarification.
Comments on the Quality of English LanguageThe text is fully understandable.
In several places there is a wrong use of article "the".
Sentences starting with "However" or "Moreover" should be rephrased.
In few places, sentences need to be reformulated.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsAuthors reviewed this MS and I have not more suggestions, and agree with their reviewing.
Author Response
Dear reviewer,
Thank you so much for all the comments for this manuscript and they are very helpful to us.
Best regards,
Yu-Hsuan Liang
Reviewer 4 Report
Comments and Suggestions for AuthorsThe authors have revised the manuscript as per suggestions. Consider it for publication in its present form.
Author Response
Dear reviewer,
Thank you so much for all the comments for this manuscript and they are very helpful to us.
Best regards,
Yu-Hsuan Liang
Reviewer 5 Report
Comments and Suggestions for AuthorsYu-Hsuan Liang, Po-Chao Wu, Shail Vijeta Ekka, Kuo-Fang Huang, Der-Chuen Lee.
Iron and molybdenum isotope applications for tracing industrial contamination in a highly polluted river
Minor
Fig. 1
A larger scale sub-figure should be added showing the location of contamination sources and sampling points.
Comments for author File: Comments.pdf
Author Response
Please see the attachment
Author Response File: Author Response.pdf
