The Impact of Dissolved Organic Matter on Photodegradation Rates, Byproduct Formations, and Degradation Pathways for Two Neonicotinoid Insecticides in Simulated River Waters

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript (sustainability-2825282) "Impact of Dissolved Organic Matter on Photodegradation Rates, Byproduct Formations, and Degradation Pathways for Two Neonicotinoid Insecticides in Simulated River Waters" provides valuable insights into the environmental behavior of neonicotinoids. The experimental design is robust, and the use of different quenching agents to explore direct and indirect photolysis is commendable. However, there are several areas where the manuscript could be improved:

l  Introduction: Please add the innovation and contribution of this study in the last paragph.

l  While the methodology is generally well-described, more detailed information about the selection of DOM sources and their characterization would enhance the study's credibility.

l  Consider including additional information on the control measures for experimental variables, such as light intensity and temperature.

l  More detailed interpretation of results in the context of environmental impact would be valuable.

l  Tables and figures are informative, yet they could be more effectively integrated into the text with clearer descriptions and discussions of their significance.

l  The discussion section could be expanded to better highlight the environmental implications of your findings. Comparisons with existing literature and potential applications of this research in environmental monitoring and management would be beneficial. Consider comparing your findings with existing literature more extensively to highlight the contribution of your research to the field.

l  The comparison of different DOM treatments is intriguing, but the discussion could be enhanced by delving deeper into the mechanistic implications of these findings.

l  A more critical analysis of the limitations and potential biases in your study is recommended.

l  References: Ensure that all references are up-to-date and relevant, particularly those relating to the environmental impact of neonicotinoids and photodegradation processes.

l  Conclusion: The conclusion section could be more robust, summarizing key findings with numeric results and their implications more succinctly. Please also provide clearer recommendations for future research or practical applications of your findings.

Comments on the Quality of English Language

Some minor issues on the language could be checked and addressed.

Author Response

We appreciate the reviewers’ suggestions and we have made amendments with track changes throughout the document and outlined in the reviewer response document below. We appreciate your reconsideration for publication.

 

Reviewer 1:

1. Introduction: Please add the innovation and contribution of this study in the last paragraph.

We have added the following at the end of the paragraph:

“This study offers unique insight to the potential role DOM have on sustainable water quality related to these two neonicotinoid degradation pathways and byproduct formations, particularly regarding ecotoxicity and formation of toxic byproducts.”

 

2. While the methodology is generally well-described, more detailed information about the selection of DOM sources and their characterization would enhance the study's credibility.

We appreciate the reviewer’s suggestion. The characterization is discussed in detail in discussion section 4.2 second paragraph. Detailed information was shared here to provide more context for the discussion.

3. Consider including additional information on the control measures for experimental variables, such as light intensity and temperature.

This is included in the Materials and Methods Section 2.2 “The solar simulator was programmed to 650 W/m² and a temperature 20˚ C.”

4. More detailed interpretation of results in the context of environmental impact would be valuable.

The following paragraph was added to the introduction to emphasize the implications of these pesticides to environmental and human health.

“Neonicotinoids are known to undergo photo-chemical transformation, which often results into the formation of potentially more toxic photodegradation byproducts harmful to aquatic and terrestrial species, and even humans [17], [18], [19]. It is important to understand which the photo-transformations occur, and potential byproducts forms in natural water environments. While there are several byproducts of imidacloprid and thiamethoxam, the most often observed in aqueous environments include imidacloprid desnitro, imidacloprid urea, imidacloprid olefin, 6-Chloronicotinic acid, 6-Chloronicotinic aldehyde, 6-Chloro-N-methylnicotinamide, 6-Hydroxynicotinic acid, clothianidin and thiamethoxam urea [2], [20]. Ecotoxicity limits for these byproducts have not yet been established, with the exception of clothianidin, which is a registered insecticide. However, some of these byproducts can often be as toxic or more toxic than the parent insecticide [14], [21], [22]. Higher toxicity has been reported for imidacloprid-desnitro, where the byproduct has been observed to trigger strong nicotinic responses in humans [6] and ovarian antral follicle growth [23]. Negative impacts of both the parent compounds and byproducts have also been observed in nontarget organisms including pollinators and aquatic invertebrates [24], [25], [26], [27].”

 

 

 

5. Tables and figures are informative, yet they could be more effectively integrated into the text with clearer descriptions and discussions of their significance.

We have attempted to integrate them more into the results section of the document. For example the following was added in Section 3.1.1:

“Table 1 provides first-order rate constants for degradation occurring during first 12 h, for all experiments, while Figures 1 -rough 3 provide overall results for the entire 36 h and include light and dark phases”

6. The discussion section could be expanded to better highlight the environmental implications of your findings. Comparisons with existing literature and potential applications of this research in environmental monitoring and management would be beneficial. Consider comparing your findings with existing literature more extensively to highlight the contribution of your research to the field.

The following paragraph was added to the discussion:

“Based on findings in this study, DOM composition impacts byproduct formations. Specifically, imidacloprid desnitro was observed to increase in MIS DOM. Recent reports of increased human health concerns regarding imidacloprid desnitro emphasizes the need to identify transformation hotspots and prevention. Further, imidacloprid desnitro has been observed to be less effectively removed by granular activated carbon compared to its parent [56], increasing potential occurrence in drinking water source.”

 

7. The comparison of different DOM treatments is intriguing, but the discussion could be enhanced by delving deeper into the mechanistic implications of these findings.

We thank the reviewer for this suggestion. We have added the following to second to last paragraph in Section 4.2:

“Based on findings in this study, DOM composition impacts byproduct formations. Specifically, imidacloprid desnitro was observed to increase in MIS DOM. Recent reports of increased human health concerns regarding imidacloprid desnitro emphasizes the need to identify transformation hotspots and prevention. Further, imidacloprid desnitro has been observed to be less effectively removed by granular activated carbon compared to its parent [56], increasing potential occurrence in drinking water sources.”

 

8. A more critical analysis of the limitations and potential biases in your study is recommended. 

We thank the reviewer for this suggestion. We have added the following to the last paragraph in Section 4.2:

“While the organic matter used in this study provides a baseline for better understanding implications of DOM to photolysis of these two insecticides, there are limitations of using a photosimulator with constant light applications and using only one initial concentration of the DOM and insecticides. Future studies should consider implications of DOM at varying concentrations and more CDOM sources along with the implications of the insecticides at varying concentrations. Water taken from local waterways should also be considered to provide more realistic physiochemical properties.”

 

9. References: Ensure that all references are up-to-date and relevant, particularly those relating to the environmental impact of neonicotinoids and photodegradation processes.

Several references were added from 2020 through 2023 on these topics including:

10. Raschitor, A. Romero, S. Sanches, V. J. Pereira, J. G. Crespo, and J. Llanos, “Degradation of neonicotinoids and caffeine from surface water by photolysis,” Molecules, vol. 26, no. 23, 2021, doi: 10.3390/molecules26237277.
11. Loser et al., “Acute effects of the imidacloprid metabolite desnitro-imidacloprid on human nACh receptors relevant for neuronal signaling,” Arch Toxicol, vol. 95, no. 12, pp. 3695–3716, 2021, doi: 10.1007/s00204-021-03168-z.
12. Wan, Q. Han, Y. Wang, and Z. He, “Five degradates of imidacloprid in source water, treated water, and tap water in Wuhan, central China,” Science of The Total Environment, vol. 741, p. 140227, 2020, doi: https://doi.org/10.1016/j.scitotenv.2020.140227.
13. Wang, X. Zhang, L. Fan, L. Su, and Y. Zhao, “Photolysis mechanism of eleven insecticides under simulated sunlight irradiation: Kinetics, pathway and QSAR,” Chemosphere, vol. 334, p. 138968, 2023, doi: https://doi.org/10.1016/j.chemosphere.2023.138968.
14. Fan et al., “Relationship between photolysis mechanism and photo-enhanced toxicity to Vibrio Fischeri for neonicotinoids with cyano-amidine and nitroguanidine structures,” Aquatic Toxicology, vol. 257, p. 106443, 2023, doi: https://doi.org/10.1016/j.aquatox.2023.106443.
15. Hashimoto et al., “Occurrence of imidacloprid and its transformation product (imidacloprid-nitroguanidine) in rivers during an irrigating and soil puddling duration,” Microchemical Journal, vol. 153, p. 104496, 2020, doi: https://doi.org/10.1016/j.microc.2019.104496.
16. E. Mourikes, R. Santacruz Márquez, A. Deviney, A. M. Neff, M. J. Laws, and J. A. Flaws, “Imidacloprid and Its Bioactive Metabolite, Desnitro-Imidacloprid, Differentially Affect Ovarian Antral Follicle Growth, Morphology, and Hormone Synthesis In Vitro,” Toxics, vol. 11, no. 4. 2023. doi: 10.3390/toxics11040349.
17. A. Thompson et al., “A critical review on the potential impacts of neonicotinoid insecticide use: Current knowledge of environmental fate, toxicity, and implications for human health,” Environ Sci Process Impacts, vol. 22, no. 6, pp. 1315–1346, 2020, doi: 10.1039/c9em00586b.
18. Satiroff, T. L. Messer, A. R. Mittelstet, and D. D. Snow, “Pesticide Occurrence and Persistence Entering Recreational Lakes in Watersheds of Varying Land Uses,” Environmental Pollution, vol. In Press, 2021.
19. D. Snow et al., “Legacy and current pesticide residues in Syr Darya, Kazakhstan: Contamination status, seasonal variation and preliminary ecological risk assessment,” Water Res, vol. 184, p. 116141, 2020, doi: 10.1016/j.watres.2020.116141.

 

10. Conclusion: The conclusion section could be more robust, summarizing key findings with numeric results and their implications more succinctly. Please also provide clearer recommendations for future research or practical applications of your findings.

More details and clearer recommendations were added to the conclusions.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript examines the effect of DOM on photodegradation of two neonicotinoid insecticides (imidacloprid and thiamethoxam) in simulated river waters. The investigation includes direct and indirect photolysis using different water matrices, DOM sources, and quenching agents. The results reveal varying photodegradation rates and byproduct formations, shedding light on the potential influence of DOM on the sustainability of river systems. The manuscript is a valuable contribution and is relevant to and of great interest to the journal's audience. However, the manuscript would be improved if the following points were addressed:

1. Line 21; 0.156 h^-1 to 0.531 h^-1 → 0.156 to 0.531 h^-1 (here and throughout the manuscript).

2. Lines 41:42; Please cite more examples.

3. Line 46; It will be better if the authors added a paragraph highlighting the potential byproducts of imidacloprid and thiamethoxam.

4. Sections 2.2. and 2.3; Are there any references or standards to support the experiments used?

5. Line 140; Please cite (EPA Method 5310D) and add it to the reference list.

6. Line 235; Wang et al. (2017) → Wang et al. [25] (here and throughout the manuscript).

7. Line 443; [36] has → Qu et al. [36] has

8. Conclusions; The presented environmental implications and future research directions are noteworthy, but you should give more space to the study findings.

9. References style in the main text and references list should be revised following the journal instructions.

Author Response

We appreciate the reviewers’ suggestions and we have made amendments with track changes throughout the document and outlined in the reviewer response document below. We appreciate your reconsideration for publication.

Reviewer 2:

1. Line 21; 0.156 h^-1to 0.531 h^-1 → 0.156 to 0.531 h^-1(here and throughout the manuscript).

This has been corrected throughout the manuscript.

 

 

2. Lines 41:42; Please cite more examples.  

This has been corrected throughout the manuscript.

 

3. Line 46; It will be better if the authors added a paragraph highlighting the potential byproducts of imidacloprid and thiamethoxam.

The following paragraph was added to the introduction to emphasize the implications of these pesticides to environmental and human health.

“Neonicotinoids are known to undergo photo-chemical transformation, which often results into the formation of potentially more toxic photodegradation byproducts harmful to aquatic and terrestrial species, and even humans [17], [18], [19]. It is important to understand which the photo-transformations occur, and potential byproducts forms in natural water environments. While there are several byproducts of imidacloprid and thiamethoxam, the most often observed in aqueous environments include imidacloprid desnitro, imidacloprid urea, imidacloprid olefin, 6-Chloronicotinic acid, 6-Chloronicotinic aldehyde, 6-Chloro-N-methylnicotinamide, 6-Hydroxynicotinic acid, clothianidin and thiamethoxam urea [2], [20]. Ecotoxicity limits for these byproducts have not yet been established, with the exception of clothianidin, which is a registered insecticide. However, some of these byproducts can often be as toxic or more toxic than the parent insecticide [14], [21], [22]. Higher toxicity has been reported for imidacloprid-desnitro, where the byproduct has been observed to trigger strong nicotinic responses in humans [6] and ovarian antral follicle growth [23]. Negative impacts of both the parent compounds and byproducts have also been observed in nontarget organisms including pollinators and aquatic invertebrates [24], [25], [26], [27].”

 

4. Sections 2.2. and 2.3; Are there any references or standards to support the experiments used?

This has been added throughout the manuscript.

 

5. Line 140; Please cite (EPA Method 5310D) and add it to the reference list.

This has been corrected in the manuscript.

 

6. Line 235; Wang et al. (2017) → Wang et al. [25] (here and throughout the manuscript).

This has been corrected.

 

7. Line 443; [36] has → Qu et al. [36] has

 This has been corrected.

 

8. Conclusions; The presented environmental implications and future research directions are noteworthy, but you should give more space to the study findings.

More details and clearer recommendations were added to the conclusions.

 

9. References style in the main text and references list should be revised following the journal instructions.

This has been corrected.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The work is great. In my opinion, only minor things need to be changed.

 

Line 121 Please correct the mistake in “Instumentation”

 

Line 146-151 Please specify why you include the Modelling of Degradation Kinetics stage in the Methods section.

 

Line 184-187 I think the sentence “In each of the experiments…” must be replaced in the Materials and Methods section.

 

 

Line 236-237 This is a discussion of the results, put it into the Discussion section

Author Response

We appreciate the reviewers’ suggestions and we have made amendments with track changes throughout the document and outlined in the reviewer response document below. We appreciate your reconsideration for publication.

Reviewer 3:

1. Line 121 Please correct the mistake in “Instumentation”

Spelling has been corrected.

2. Line 146-151 Please specify why you include the Modelling of Degradation Kinetics stage in the Methods section.

The following edits were made to address this concern: “To quantify degradation rates, changes in insecticide concentrations were fit to a first order decay response model for the first 12 hours of the experiment similar to past photodegradation studies [41], [42].”

3. Line 184-187 I think the sentence “In each of the experiments…” must be replaced in the Materials and Methods section.

This sentence has been to section “2.7 Statistics”.

4. Line 236-237 This is a discussion of the results, put it into the Discussion section

This sentence was moved into a new section “4.1 Degradation Kinetics Implications” to provide more discussion of the environmental implications of degradation and byproduct formations.

Author Response File: Author Response.pdf