Soil-biodegradable plastic films do not decompose in a lake sediment over 9 months of incubation

van Grinsven, Sigrid; Schubert, Carsten

doi:https://doi.org/10.5194/egusphere-2023-400

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https://doi.org/10.5194/egusphere-2023-400

Preprints

04 Apr 2023

| 04 Apr 2023

Soil-biodegradable plastic films do not decompose in a lake sediment over 9 months of incubation

Sigrid van Grinsven and Carsten Schubert

Abstract. Agriculture relies heavily on the use of plastic mulch films, which increase crop yields and lower water demands. Research has shown that agricultural mulch film may be transported to aquatic environments. We tested the mineralization of soil-biodegradable agricultural mulch films in freshwater lake sediments. Two types of commercial soil-biodegradable mulch films were incubated within lake sediment cores, and the production of CO₂ and CH₄ was followed over time. After the 40-week incubation period, films were visually intact and showed no signs of mineralization. Gas analyses showed no additional production of either CO₂ or CH₄ in the degradable film incubations, compared to control or PE plastic incubations. We conclude that the tested soil-biodegradable mulch films have a low biodegradability in lake sediments, likely reflecting that the lake sediment lacks active microbial degraders. Our results highlight the importance of preventing transport of soil-biodegradable mulch films from agricultural soils to surrounding aquatic environments.

Received: 05 Mar 2023 – Discussion started: 04 Apr 2023

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Journal article(s) based on this preprint

13 Oct 2023

| Highlight paper

Soil-biodegradable plastic films do not decompose in a lake sediment over 9 months of incubation

Sigrid van Grinsven and Carsten Schubert

Biogeosciences, 20, 4213–4220, https://doi.org/10.5194/bg-20-4213-2023,https://doi.org/10.5194/bg-20-4213-2023, 2023

Short summary Co-editor-in-chief

Sigrid van Grinsven and Carsten Schubert

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-400', Anonymous Referee #1, 02 May 2023

The present manuscript shows an interesting subject strongly linked to ecofriendly agriculture and sustainability. However, it needs some adjustments according to notes made into manuscript file attached here.

Citation: https://doi.org/10.5194/egusphere-2023-400-RC1
- AC1:
  'Reply on RC1', Sigrid van Grinsven, 15 Aug 2023
  
  We would like to sincerely thank this reviewer for the useful feedback, which increased the quality of this manuscript.
  We have adapted the manuscript at each of the locations where this reviewer added comments, as can be seen in the uploaded document. We have not added individual replies to the reviewer's comments, as the format did not easily allow for that. We hope it is sufficiently clear for the reviewer based on the changes in the manuscript text, how we have used their comments. If needed, we can provide extra explanations.
  We have also added and adapted text based on the comments of reviewer 2, which often showed overlap with the comments of reviewer 1. Therefore, this reviewer will see additional changes to the manuscript, also outside the sections where this reviewer provided comments.
  
  Citation: https://doi.org/10.5194/egusphere-2023-400-AC1
  - AC3: 'Reply on AC1', Sigrid van Grinsven, 15 Aug 2023
    
    I do not see a way to provide the reviewers or editor with the revised manuscript, but it is ready and can be made available immediately when requested.
    
    Citation: https://doi.org/10.5194/egusphere-2023-400-AC3
RC2:
'Comment on egusphere-2023-400', Anonymous Referee #2, 29 Jul 2023

General Comments:
The research investigates the biodegradation of soil-biodegradable agricultural mulch films in freshwater lake sediments. The study highlights the importance of preventing the transport of these films from agricultural fields to neighboring aquatic ecosystems for sustainable waste management in agriculture. The method section provides a clear description of the experimental setup, although some aspects could be further improved for a more comprehensive analysis.
Major Comments:
Sample Variance and Trends: The paper should address the observed large individual sample variance and discuss the different trends shown in Figure 3, even though they are statistically insignificant. This could help readers better understand the variability in the results.
Inclusion of Non-Results: Lines 223-234 appear to be non-results from another study and should be removed from the Results section. Focus solely on the findings of the current research.
Microscope Results: The visualization of plastic film surfaces using microscopy is a significant aspect of the study. The results of the visualization, including details on fragmentation (micro and nanoplastics) and the presence of microbes, should be explicitly presented in the main text to enhance the paper's clarity.
Photodegradation Overlooked: The study's limitation of conducting experiments in dark conditions overlooks the potential of photodegradation, especially in shallow freshwater environments with strong sunlight (UV) penetration to sediment. This limitation should be discussed to provide a more comprehensive understanding of the degradation process.
Minor comments:
Duration of Incubation Period: While the 40-week incubation period appears reasonable, it would be beneficial to discuss whether this duration aligns with similar studies or if any limitations arise due to this timeframe.
Generalization to Other Environments: The research is conducted in Lake Lucerne, Switzerland, which may have unique environmental conditions. Therefore, caution should be exercised when generalizing the findings to other freshwater systems with different sediment and microbial characteristics. This should be mentioned in the paper's discussion section.
Overall, the paper contributes new insights into the degradation of soil-biodegradable agricultural mulch films in freshwater lake sediments. Addressing the above-mentioned concerns would enhance the scientific robustness of the study and improve its potential impact in the field of sustainable waste management practices in agriculture.

Citation: https://doi.org/10.5194/egusphere-2023-400-RC2
- AC2:
  'Reply on RC2', Sigrid van Grinsven, 15 Aug 2023
  
  Re: We thank this reviewer for the constructive feedback on this manuscript, which helped us further improve the quality. Below, we have provided individual replies to the reviewer's comments. In the revised version of the manuscript, the changes that are made based on this, and reviewer 1's comments, are visible.
  
  General Comments:
  The research investigates the biodegradation of soil-biodegradable agricultural mulch films in freshwater lake sediments. The study highlights the importance of preventing the transport of these films from agricultural fields to neighboring aquatic ecosystems for sustainable waste management in agriculture. The method section provides a clear description of the experimental setup, although some aspects could be further improved for a more comprehensive analysis.
  Major Comments:
  Sample Variance and Trends: The paper should address the observed large individual sample variance and discuss the different trends shown in Figure 3, even though they are statistically insignificant. This could help readers better understand the variability in the results.
  Re: We have currently explained the different trends of the treatments in the results (line 240-269), while also stressing that these were not statistically significant. We have added and adjusted several sentences in this piece, also in reaction to comments by Reviewer 1.
  We have chosen to not further discuss the findings on the trends between the treatments in the discussion, because of their statistical insignificance. Discussing them in the discussion section would give more value to them then we considered appropriate given the statistics.
  We have added extra text on the individual sample variation within treatments to the discussion, to give possible explanations for this variation. This will allow the reader to assess the within- and between treatment variations better, we hope. (lines 315-325).
  Inclusion of Non-Results: Lines 223-234 appear to be non-results from another study and should be removed from the Results section. Focus solely on the findings of the current research.
  Re: Thank you for this observation, which is completely correct. We have removed this part from the results section.
  Microscope Results: The visualization of plastic film surfaces using microscopy is a significant aspect of the study. The results of the visualization, including details on fragmentation (micro and nanoplastics) and the presence of microbes, should be explicitly presented in the main text to enhance the paper's clarity.
  Re: We have deliberately given the microscopy part of this study a relatively small role, because it is not quantitative. We consider it an interesting extra method of assessing the degradation, but we have not used it in enough detail to allow a quantification of the fragmentation, for example. Therefore, we have included it in its current form. We hope that in this form, it remains clear to the reader that the microscopy part is additional, but cannot provide quantitative results on the degradation of the plastics.
  Photodegradation Overlooked: The study's limitation of conducting experiments in dark conditions overlooks the potential of photodegradation, especially in shallow freshwater environments with strong sunlight (UV) penetration to sediment. This limitation should be discussed to provide a more comprehensive understanding of the degradation process.
  Re: Thank you for this suggestion. We have added text to the discussion on the relevance of photodegradation for plastic degradation in soil, shallow water, and deep water environments (lines 362 – 369).
  Minor comments:
  Duration of Incubation Period: While the 40-week incubation period appears reasonable, it would be beneficial to discuss whether this duration aligns with similar studies or if any limitations arise due to this timeframe.
  Re: In the discussion, we mention the duration and degradation during that time, of other studies (296-300) and we mention the potential problems regarding oxygen limitation in the methods section (153-156 and 194-197).
  Generalization to Other Environments: The research is conducted in Lake Lucerne, Switzerland, which may have unique environmental conditions. Therefore, caution should be exercised when generalizing the findings to other freshwater systems with different sediment and microbial characteristics. This should be mentioned in the paper's discussion section.
  Re: we have now added text on the need for future research on both priming effects of soil pre-incubation, and on the relevance of the lake sediment characteristics, to the discussion (383-395).
  Overall, the paper contributes new insights into the degradation of soil-biodegradable agricultural mulch films in freshwater lake sediments. Addressing the above-mentioned concerns would enhance the scientific robustness of the study and improve its potential impact in the field of sustainable waste management practices in agriculture.
  Re: Thank you for your help in improving this manuscript!
  
  Citation: https://doi.org/10.5194/egusphere-2023-400-AC2
  - AC4: 'Reply on AC2', Sigrid van Grinsven, 15 Aug 2023
    
    I do not see a way to provide the reviewers or editor with the revised manuscript, but it is ready and can be made available immediately when requested.
    
    Citation: https://doi.org/10.5194/egusphere-2023-400-AC4

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-400', Anonymous Referee #1, 02 May 2023

The present manuscript shows an interesting subject strongly linked to ecofriendly agriculture and sustainability. However, it needs some adjustments according to notes made into manuscript file attached here.

Citation: https://doi.org/10.5194/egusphere-2023-400-RC1
- AC1:
  'Reply on RC1', Sigrid van Grinsven, 15 Aug 2023
  
  We would like to sincerely thank this reviewer for the useful feedback, which increased the quality of this manuscript.
  We have adapted the manuscript at each of the locations where this reviewer added comments, as can be seen in the uploaded document. We have not added individual replies to the reviewer's comments, as the format did not easily allow for that. We hope it is sufficiently clear for the reviewer based on the changes in the manuscript text, how we have used their comments. If needed, we can provide extra explanations.
  We have also added and adapted text based on the comments of reviewer 2, which often showed overlap with the comments of reviewer 1. Therefore, this reviewer will see additional changes to the manuscript, also outside the sections where this reviewer provided comments.
  
  Citation: https://doi.org/10.5194/egusphere-2023-400-AC1
  - AC3: 'Reply on AC1', Sigrid van Grinsven, 15 Aug 2023
    
    I do not see a way to provide the reviewers or editor with the revised manuscript, but it is ready and can be made available immediately when requested.
    
    Citation: https://doi.org/10.5194/egusphere-2023-400-AC3
RC2:
'Comment on egusphere-2023-400', Anonymous Referee #2, 29 Jul 2023

General Comments:
The research investigates the biodegradation of soil-biodegradable agricultural mulch films in freshwater lake sediments. The study highlights the importance of preventing the transport of these films from agricultural fields to neighboring aquatic ecosystems for sustainable waste management in agriculture. The method section provides a clear description of the experimental setup, although some aspects could be further improved for a more comprehensive analysis.
Major Comments:
Sample Variance and Trends: The paper should address the observed large individual sample variance and discuss the different trends shown in Figure 3, even though they are statistically insignificant. This could help readers better understand the variability in the results.
Inclusion of Non-Results: Lines 223-234 appear to be non-results from another study and should be removed from the Results section. Focus solely on the findings of the current research.
Microscope Results: The visualization of plastic film surfaces using microscopy is a significant aspect of the study. The results of the visualization, including details on fragmentation (micro and nanoplastics) and the presence of microbes, should be explicitly presented in the main text to enhance the paper's clarity.
Photodegradation Overlooked: The study's limitation of conducting experiments in dark conditions overlooks the potential of photodegradation, especially in shallow freshwater environments with strong sunlight (UV) penetration to sediment. This limitation should be discussed to provide a more comprehensive understanding of the degradation process.
Minor comments:
Duration of Incubation Period: While the 40-week incubation period appears reasonable, it would be beneficial to discuss whether this duration aligns with similar studies or if any limitations arise due to this timeframe.
Generalization to Other Environments: The research is conducted in Lake Lucerne, Switzerland, which may have unique environmental conditions. Therefore, caution should be exercised when generalizing the findings to other freshwater systems with different sediment and microbial characteristics. This should be mentioned in the paper's discussion section.
Overall, the paper contributes new insights into the degradation of soil-biodegradable agricultural mulch films in freshwater lake sediments. Addressing the above-mentioned concerns would enhance the scientific robustness of the study and improve its potential impact in the field of sustainable waste management practices in agriculture.

Citation: https://doi.org/10.5194/egusphere-2023-400-RC2
- AC2:
  'Reply on RC2', Sigrid van Grinsven, 15 Aug 2023
  
  Re: We thank this reviewer for the constructive feedback on this manuscript, which helped us further improve the quality. Below, we have provided individual replies to the reviewer's comments. In the revised version of the manuscript, the changes that are made based on this, and reviewer 1's comments, are visible.
  
  General Comments:
  The research investigates the biodegradation of soil-biodegradable agricultural mulch films in freshwater lake sediments. The study highlights the importance of preventing the transport of these films from agricultural fields to neighboring aquatic ecosystems for sustainable waste management in agriculture. The method section provides a clear description of the experimental setup, although some aspects could be further improved for a more comprehensive analysis.
  Major Comments:
  Sample Variance and Trends: The paper should address the observed large individual sample variance and discuss the different trends shown in Figure 3, even though they are statistically insignificant. This could help readers better understand the variability in the results.
  Re: We have currently explained the different trends of the treatments in the results (line 240-269), while also stressing that these were not statistically significant. We have added and adjusted several sentences in this piece, also in reaction to comments by Reviewer 1.
  We have chosen to not further discuss the findings on the trends between the treatments in the discussion, because of their statistical insignificance. Discussing them in the discussion section would give more value to them then we considered appropriate given the statistics.
  We have added extra text on the individual sample variation within treatments to the discussion, to give possible explanations for this variation. This will allow the reader to assess the within- and between treatment variations better, we hope. (lines 315-325).
  Inclusion of Non-Results: Lines 223-234 appear to be non-results from another study and should be removed from the Results section. Focus solely on the findings of the current research.
  Re: Thank you for this observation, which is completely correct. We have removed this part from the results section.
  Microscope Results: The visualization of plastic film surfaces using microscopy is a significant aspect of the study. The results of the visualization, including details on fragmentation (micro and nanoplastics) and the presence of microbes, should be explicitly presented in the main text to enhance the paper's clarity.
  Re: We have deliberately given the microscopy part of this study a relatively small role, because it is not quantitative. We consider it an interesting extra method of assessing the degradation, but we have not used it in enough detail to allow a quantification of the fragmentation, for example. Therefore, we have included it in its current form. We hope that in this form, it remains clear to the reader that the microscopy part is additional, but cannot provide quantitative results on the degradation of the plastics.
  Photodegradation Overlooked: The study's limitation of conducting experiments in dark conditions overlooks the potential of photodegradation, especially in shallow freshwater environments with strong sunlight (UV) penetration to sediment. This limitation should be discussed to provide a more comprehensive understanding of the degradation process.
  Re: Thank you for this suggestion. We have added text to the discussion on the relevance of photodegradation for plastic degradation in soil, shallow water, and deep water environments (lines 362 – 369).
  Minor comments:
  Duration of Incubation Period: While the 40-week incubation period appears reasonable, it would be beneficial to discuss whether this duration aligns with similar studies or if any limitations arise due to this timeframe.
  Re: In the discussion, we mention the duration and degradation during that time, of other studies (296-300) and we mention the potential problems regarding oxygen limitation in the methods section (153-156 and 194-197).
  Generalization to Other Environments: The research is conducted in Lake Lucerne, Switzerland, which may have unique environmental conditions. Therefore, caution should be exercised when generalizing the findings to other freshwater systems with different sediment and microbial characteristics. This should be mentioned in the paper's discussion section.
  Re: we have now added text on the need for future research on both priming effects of soil pre-incubation, and on the relevance of the lake sediment characteristics, to the discussion (383-395).
  Overall, the paper contributes new insights into the degradation of soil-biodegradable agricultural mulch films in freshwater lake sediments. Addressing the above-mentioned concerns would enhance the scientific robustness of the study and improve its potential impact in the field of sustainable waste management practices in agriculture.
  Re: Thank you for your help in improving this manuscript!
  
  Citation: https://doi.org/10.5194/egusphere-2023-400-AC2
  - AC4: 'Reply on AC2', Sigrid van Grinsven, 15 Aug 2023
    
    I do not see a way to provide the reviewers or editor with the revised manuscript, but it is ready and can be made available immediately when requested.
    
    Citation: https://doi.org/10.5194/egusphere-2023-400-AC4

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

ED: Publish subject to minor revisions (review by editor) (30 Aug 2023) by Tina Treude

AR by Sigrid van Grinsven on behalf of the Authors (30 Aug 2023) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (31 Aug 2023) by Tina Treude

AR by Sigrid van Grinsven on behalf of the Authors (08 Sep 2023) Manuscript

Journal article(s) based on this preprint

13 Oct 2023

| Highlight paper

Soil-biodegradable plastic films do not decompose in a lake sediment over 9 months of incubation

Sigrid van Grinsven and Carsten Schubert

Biogeosciences, 20, 4213–4220, https://doi.org/10.5194/bg-20-4213-2023,https://doi.org/10.5194/bg-20-4213-2023, 2023

Short summary Co-editor-in-chief

Sigrid van Grinsven and Carsten Schubert

Supplement

https://doi.org/10.5194/egusphere-2023-400-supplement

Sigrid van Grinsven and Carsten Schubert

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

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The findings of this study are interesting to a broader audience as it demonstrates that supposedly biodegradable mulch films used for agricultural purposes remain unchanged in lake sediments over several months. The results indicate that lake sediments are a place of long-term storage rather than a place of degradation for this form of plastic.

Short summary

Agriculture relies heavily on plastic mulch films, which may be transported to aquatic environments. We investigated the mineralization of soil-biodegradable agricultural mulch films in lake sediments. After 40-weeks, films were intact and no extra CO₂ or CH₄ was produced. We conclude that the used mulch films have a low biodegradability in lake sediments, because it lacks microbes capable of the specific degradation reactions needed to break down the biodegradable plastics provided here.


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