Exploring Sustainable Solutions: Dynamic Adsorption, Isotherm Models, and Kinetics of Organic Contaminants on Polystyrene Microplastics

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study investigates the dynamics of the adsorption of organochlorine pesticides (OCPs) onto microplastics, which are emerging contaminants of significant concern. Understanding the interaction between these pollutants is crucial, not only for the research community but also for policymakers and the public.

Line 15: In this section, microplastics are introduced first, followed by a sudden mention of the adsorption of organic compounds. It would be more logical to further elaborate on organic compounds before discussing their adsorption.

Lines 77-79: Please consider citing a recent study on the global spread of microplastics:

Xiao, S., Cui, Y., Brahney, J., Mahowald, N.M. and Li, Q., 2023. Long-distance atmospheric transport of microplastic fibres influenced by their shapes. Nature Geoscience, 16(10), pp.863-870.

Line 85: It would be beneficial to reference previous studies on the adsorption mechanisms of various materials onto microplastics. While this may be the first study focusing on the adsorption of OCPs on microplastics, research on the adsorption of heavy metals, other hazardous materials, and kinetic dynamics likely exists. Highlighting these studies can help identify the knowledge gap your research addresses.

Lines 117-120: Please clarify why these particular substances were selected for investigation.

Line 130: It would be helpful to provide a brief explanation of why pH and contact time are critical variables in this context.

Equations 1-3: Please ensure your mathematical notations are consistent with current standards. Additionally, ensure the same level of rigor is applied throughout the manuscript.

Lines 425-436: The mechanisms proposed here lack solid theoretical support and are currently presented more as a discussion. It is advisable to seek additional evidence to substantiate these conclusions.

Figures: The font size in the figures is too small. Please increase it to improve readability.

Author Response

Q1: Line 15: In this section, microplastics are introduced first, followed by a sudden mention of the adsorption of organic compounds. It would be more logical to further elaborate on organic compounds before discussing their adsorption.

A1: Thank you for your valuable feedback. I have revised the section to provide a clearer context by elaborating on organic compounds before discussing their adsorption on microplastics. This change aims to enhance the logical flow and clarity of the information presented.

 

Q2: Lines 77-79: Please consider citing a recent study on the global spread of microplastics:

Xiao, S., Cui, Y., Brahney, J., Mahowald, N.M. and Li, Q., 2023. Long-distance atmospheric transport of microplastic fibres influenced by their shapes. Nature Geoscience, 16(10), pp.863-870.

A2: Thank you for the suggestion. I have incorporated the cited study by Xiao et al. (2023) to provide a more comprehensive overview of the global spread of microplastics and their atmospheric transport. Your recommendation greatly enhances the relevance of the section.

 

Q3: Line 85: It would be beneficial to reference previous studies on the adsorption mechanisms of various materials onto microplastics. While this may be the first study focusing on the adsorption of OCPs on microplastics, research on the adsorption of heavy metals, other hazardous materials, and kinetic dynamics likely exists. Highlighting these studies can help identify the knowledge gap your research addresses.

A3: Thank you for your valuable feedback. I have added a paragraph referencing previous studies on the adsorption mechanisms of various materials onto microplastics, highlighting the existing research on heavy metals and other hazardous substances. This addition emphasizes the knowledge gap our study addresses regarding the adsorption of organochlorine pesticides on microplastics. Your suggestion has significantly improved the manuscript. References added:

               Qian Liu, Haowen Wu, Jiajiao Chen, Biaohu Guo, Xiufang Zhao, Hui Lin, Wei Li, Xin Zhao, Sihao Lv, Cong Huang. Adsorption mechanism of trace heavy metals on microplastics and simulating their effect on microalgae in river. Environmental Research 214, 2022, 113777. https://doi.org/10.1016/j.envres.2022.113777.

               Sung Hee Joo, Yejin Liang, Minbeom Kim, Jaehyun Byun, Heechul Choi. Microplastics with adsorbed contaminants: Mechanisms and Treatment. Environmental Challenges 3, 2021, 100042. https://doi.org/10.1016/j.envc.2021.100042.

 

 

Q4: Lines 117-120: Please clarify why these particular substances were selected for investigation.

A4: The selection of the 16 organochlorine pesticides for this investigation was driven by their historical prevalence, persistent nature, and significant environmental and health impacts. As highlighted in the introduction, OCPs have been widely used until their harmful effects became evident, resulting in their eventual ban in many countries (refer to Introduction, paragraphs 1-3). These particular compounds are known to persist in the environment, bioaccumulate in food webs, and pose risks to human and ecosystem health. Moreover, the European Union's stringent regulations on permissible pesticide limits in drinking water underline the ongoing concerns regarding these pollutants (refer to Introduction, paragraph 4). Thus, investigating the interactions between these selected OCPs and microplastics is crucial for understanding their environmental fate and potential risks associated with modern pollution.

 

Q5: Line 130: It would be helpful to provide a brief explanation of why pH and contact time are critical variables in this context.

A5: Thank you for your insightful comment regarding the importance of pH and contact time in our study. We have added a paragraph to the manuscript that briefly explains their critical roles in the interaction between organochlorine pesticides and microplastics. This addition emphasizes how pH influences the physicochemical properties of both the pesticides and microplastics, while contact time affects the extent of adsorption. We believe this clarification enhances the overall understanding of our research.

 

 

Q6: Equations 1-3: Please ensure your mathematical notations are consistent with current standards. Additionally, ensure the same level of rigor is applied throughout the manuscript.

A6: Thank you for your valuable feedback regarding the consistency of our mathematical notations and the overall rigor of the manuscript. We have revised the manuscript to ensure that all mathematical notations adhere to current standards and that a consistent level of rigor is applied throughout the document. We appreciate your attention to detail, which has helped to improve the clarity and precision of our work.

 

Q7: Lines 425-436: The mechanisms proposed here lack solid theoretical support and are currently presented more as a discussion. It is advisable to seek additional evidence to substantiate these conclusions.

A7: Thank you for your insightful comment regarding the need for stronger theoretical support for the proposed mechanisms. We have added a paragraph to the manuscript that discusses the alignment of our findings with established theories on adsorption kinetics and surface chemistry. This addition provides a clearer theoretical framework to substantiate our conclusions. We appreciate your valuable feedback in enhancing the rigor of our work.

P.S. Tourinho, V. Kočí, S. Loureiro, C.A.M. van Gestel. Partitioning of chemical contaminants to microplastics: sorption mechanisms, environmental distribution and effects on toxicity and bioaccumulation. Environ. Pollut., 252 (2019), pp. 1246-1256. https://doi.org/10.1016/j.envpol.2019.06.030.

Chengli Zhang, Yuchen Lei, Jing Qian, Yixin Qiao, Jingchao Liu, Shuifeng Li, Lingyu Dai, Kexin Sun, Huimin Guo, Guodong Sui, Wenwen Jing. Sorption of organochlorine pesticides on polyethylene microplastics in soil suspension. Ecotoxicology and Environmental Safety 223, 2021, 112591. https://doi.org/10.1016/j.ecoenv.2021.112591.

 

Q8: Figures: The font size in the figures is too small. Please increase it to improve readability.

A8: Thank you for your constructive feedback regarding the font size in the figures. We have increased the font size to enhance readability and ensure all information is clear and accessible. We appreciate your attention to detail, which has helped improve the overall quality of our manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

A study of the adsorption of a wide range of organochlorine pesticides on polystyrene in aqueous solution is presented. A batch process with variable pH and contact time was used. A kinetic model based on the experimental results is presented. Below is a list of comments that will help improve the quality of the work.

Lines 85-86. Is it appropriate to characterize your work as “…pioneering investigation…”? Perhaps it is worth citing several works conceptually close to yours, for example [10.1016/j.ecoenv.2021.112591] or [10.1016/j.scitotenv.2022.157703].

Line 125. Specify the particle size of polystyrene. Does the small (micron) particle size impose restrictions on their use as an adsorbent?

Lines 152-159. Accuracy of GC concentration determination? Figures 1 and 2 are a complete match of points, please add the relative error

Lines 259-261. “Previous studies…” - please indicate these works.

Fig 2 – Please indicate the contact time for the pH dependence.

Lines 284-287. How does the particle size affect the efficiency of the adsorbent? If the contact area (surface) is determined by the internal area. Please provide explanations and references.

Were the experiments accompanied by the release of gases/liquid components during the interaction of organochlorine pesticides and polystyrene?

Lines 394-396. “These discrepancies between the calculated values ​​and those obtained by kinetic models can be attributed to the fact that the pseudo-order I model is less suitable for the study of adsorption of organochlorine pesticide contaminated water on polystyrene particles”. There are negleglible expressions here and earlier.

456-458. Is it possible to use PS as an adsorbent given the performance demonstrated in your work? Do the authors suggest using batch or flow systems?

Author Response

Q1: Lines 85-86. Is it appropriate to characterize your work as “…pioneering investigation…”? Perhaps it is worth citing several works conceptually close to yours, for example [10.1016/j.ecoenv.2021.112591] or [10.1016/j.scitotenv.2022.157703].

A1: Thank you for your valuable suggestion regarding the characterization of our work. We appreciate your recommendation to cite related studies, and we have revised the text to provide a more balanced perspective by referencing the suggested works. This change enhances the context of our research and acknowledges the contributions of others in the field.

Chengli Zhang, Yuchen Lei, Jing Qian, Yixin Qiao, Jingchao Liu, Shuifeng Li, Lingyu Dai, Kexin Sun, HuiminGuo, Guodong Sui, Wenwen Jing. Sorption of organochlorine pesticides on polyethylene microplastics in soil suspension. Ecotoxicology and Environmental Safety, 223, 2021, 112591. https://doi.org/10.1016/j.ecoenv.2021.112591.

Estefanía Concha-Graña, Carmen M. Moscoso-Pérez, Purificación López-Mahía, Soledad Muniategui-Lorenzo. Adsorption of pesticides and personal care products on pristine and weathered microplastics in the marine environment. Comparison between bio-based and conventional plastics. Science of The Total Environment 848, 2022, 157703. https://doi.org/10.1016/j.scitotenv.2022.157703.

 

Q2: Line 125. Specify the particle size of polystyrene. Does the small (micron) particle size impose restrictions on their use as an adsorbent?

A: Thank you for your insightful comment regarding the particle size of polystyrene. We have specified this information in the Batch experiment section. Specifically, we note that "microplastic granules with a diameter of less than 100 µm were obtained by milling and separated using a sieve."

 

 

Q3: Lines 152-159. Accuracy of GC concentration determination? Figures 1 and 2 are a complete match of points, please add the relative error.

A3: Thank you for your constructive feedback regarding the accuracy of GC concentration determination. We appreciate your suggestion and will add the relative error to Figures 1 and 2 to enhance the clarity and precision of our results. This will provide a more comprehensive understanding of the data presented.

 

Q4: Lines 259-261. “Previous studies…” - please indicate these works.

A4:  Thank you for your insightful comment. We have included the reference to the relevant review paper in the revised manuscript to provide context for the statement regarding previous studies. The citation is as follows:

Lina Fu, Jing Li, Guoyu Wang, Yaning Luan, Wei Dai. "Adsorption behavior of organic pollutants on microplastics." Ecotoxicology and Environmental Safety, 217, 2021, 112207. https://doi.org/10.1016/j.ecoenv.2021.112207.

 

Q5: Fig 2 – Please indicate the contact time for the pH dependence.

A5: Thank you for your valuable suggestion. We will specify the contact time for the pH dependence in the revised manuscript to ensure clarity and completeness of the experimental conditions.

 

 

Q6: Lines 284-287. How does the particle size affect the efficiency of the adsorbent? If the contact area (surface) is determined by the internal area. Please provide explanations and references.

A6: Thank you for your important question regarding the impact of particle size on the efficiency of the adsorbent. Particle size significantly influences the adsorption process by affecting the external surface area, internal pore structure, and accessibility to pollutants. Smaller particles typically have a larger surface area-to-volume ratio, which enhances their adsorption capacity. Additionally, the internal pore structure can play a crucial role in determining the rate and extent of adsorption.

We will incorporate a detailed explanation and relevant references addressing these points in the revised manuscript. Key studies that discuss these relationships include:

Akhmad Masykur Hadi Musthofa, Mindriany Syafila, Qomarudin Helmy. Effect of Activated Carbon Particle Size on Methylene Blue Adsorption Process in Textile Wastewater. Indones. J. Chem., 2023, 23 (2), 461 – 474. 10.22146/ijc.79784.

 

Q7: Were the experiments accompanied by the release of gases/liquid components during the interaction of organochlorine pesticides and polystyrene?

A7: Thank you for your insightful question regarding the potential release of gases or liquid components during the interaction of organochlorine pesticides and polystyrene in our experiments. We did not specifically investigate the release of gases or liquids in the current study; our focus was primarily on the adsorption behavior of the pesticides on polystyrene. However, we acknowledge that interactions between organochlorine pesticides and polystyrene could potentially lead to the release of certain components under specific conditions.

 

Q8: Lines 394-396. “These discrepancies between the calculated values ​​and those obtained by kinetic models can be attributed to the fact that the pseudo-order I model is less suitable for the study of adsorption of organochlorine pesticide contaminated water on polystyrene particles”. There are negligible expressions here and earlier.

A8: Thank you for your comment regarding the clarity of our expressions related to the kinetic models. We appreciate your feedback and will revise the wording to provide a more precise explanation of the discrepancies observed. Specifically, we will clarify that the pseudo-first-order model may not adequately capture the kinetics of adsorption for organochlorine pesticides on polystyrene particles, potentially due to the complex interactions involved. This clarification will enhance the readers' understanding of the limitations of the model in our context.

 

Q9: 456-458. Is it possible to use PS as an adsorbent given the performance demonstrated in your work? Do the authors suggest using batch or flow systems?

A9: Thank you for your question regarding the use of polystyrene (PS) as an adsorbent based on the performance demonstrated in our work. Based on our findings, PS shows promise as an effective adsorbent for organochlorine pesticides due to its high surface area and adsorption capacity. We believe that both batch and flow systems can be utilized effectively, depending on the specific application. Batch systems may provide simplicity and ease of operation for smaller-scale applications or preliminary studies, while flow systems could enhance mass transfer and allow for continuous processing in larger-scale operations. Therefore, the choice between these systems should be guided by the specific requirements of the application and the desired throughput.

Thank you again for your valuable input.