What Are Lake Beaches Made of? An Assessment of Plastic Beach Litter on the Shores of Como Bay (Italy)

Round 1

Reviewer 1 Report

This study investigated the plastic litter in lake beaches of the Como Bay, Italy. The litter density, sample composition, spatial distribution, source and potential factor influenced the spatial distribution were provided. The results were valuable for assessment of the microplastics pollution in the beach sediments.

Overall, the text is well structured and written. The working objectives are clear, the experimental design and data analysis are correct and the discussion fits the results obtained. I recommend publish of this manuscript after a minor revison.

1) "All detectable plastic litter" What's the standard for "detectable"? Visible to the naked eye or by other instrument? What's the minimum particle size for the collected plastic litter?

2)" The three categories together present 69% of beach litter" How about the other 31%? All are "unknown material" or "building material"

3) Colud any information can provide on the degradation and alteration based on the FTIR spectra?

4) The correlation analysis between litter density and local features. Besides the correlation coefficient R, the p values should also provided in the text.

5) What's the averagely impacted? How to quantify?

Author Response

Reviewer 1

This study investigated the plastic litter in lake beaches of the Como Bay, Italy. The litter density, sample composition, spatial distribution, source and potential factor influenced the spatial distribution were provided. The results were valuable for assessment of the microplastics pollution in the beach sediments.

Overall, the text is well structured and written. The working objectives are clear, the experimental design and data analysis are correct and the discussion fits the results obtained. I recommend publish of this manuscript after a minor revison.

Response: We thank the reviewer for the positive comment and for the time in providing supportive suggestions. Responses to specific comments are listed below (please note that line numbers refer to the “marked changes” version of the manuscript).

 

• "All detectable plastic litter" What's the standard for "detectable"? Visible to the naked eye or by other instrument? What's the minimum particle size for the collected plastic litter?

Response: The consideration for “detectable” include all the fragments which are visible at naked eye, and considered above the “microplastic” dimensional threshold of 5mm, defined by the Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP, http://www.gesamp.org/publications/reports-and-studies-no-90). This issue was better defined in the method section (lines 137-139).

 

2)" The three categories together present 69% of beach litter" How about the other 31%? All are "unknown material" or "building material"

Response: We thank the reviewer for this consideration. According to comment by the Reviewer 2, we have changed samples classification by categorizing Styrofoam as a packaging (previously it was categorized as “building material”). As a consequence, packaging, everyday objects and disposable objects present now as 71% of recovered beach litter. The remaining 29% include the sum of building materials, unknown materials and a small portion of biofilm carriers likely dispersed from wastewater treatment plants (5%, 23% and 1 % respectively). These values are better clarified in the result section (lines 236-245).

 

3) Colud any information can provide on the degradation and alteration based on the FTIR spectra?

Response: We thank the reviewer for raising this issue. The main aim of section 3.2. was to indicate the FTIR spectral alterations induced by ageing processes of plastics. However, considering this comment, we decided to expand this section adding some possible consequences derived from the evidenced changes in FTIR spectra observed in our study (lines 275-278; 282-283; 299-303).

 

4) The correlation analysis between litter density and local features. Besides the correlation coefficient R, the p values should also provided in the text.

Response: We thank the reviewer for this observation. We added p-values in text (lines 323-326) and in Table S3 in supplementary material.

 

5) What's the averagely impacted? How to quantify?

Response: We thank the reviewer for catching this issue. We intended to say that TP sampling point present a litter density close (and below) the overall average of all sampling sites. This is better clarified in the revised manuscript (lines 330-332).

Reviewer 2 Report

The authors claimed that “this study aims to (i) identify sources of plastic waste on beaches nearby Como city, (ii) assess the processes causing accumulation and (iii) understand the likely polymeric nature and the grade of degradation of collected plastic objects in beach sediments, in order to develop an efficient analytical protocol to extract MPs from sediments.”

 

My first major concern is that this study only provided adequate data to address the first aim, but not the second and third aims.

 

My second major concern is that this study did not provide any data of microplastics (MPs). The aims, the findings from larger-sized plastic litter and all discussion should be more carefully interpreted if the authors attempt to link this study to MPs.

 

My minor concerns are listed provided.

 

Line 53: Strictly speaking, biofouling (i.e. accumulation of organisms on surfaces where they are not wanted) is not a process of plastic degradation. Please reword.

 

Line 138: “All detectable plastic litter was collected in plastic bags…” Please comment on the possibility of contamination.

 

Line 144: “Polymeric material such as styrofoam and polyurethan have been classified as building material...” It may be more appropriate to categorise styrofoam as packaging material, instead of building material.

 

Author Response

Reviewer 2

The authors claimed that “this study aims to (i) identify sources of plastic waste on beaches nearby Como city, (ii) assess the processes causing accumulation and (iii) understand the likely polymeric nature and the grade of degradation of collected plastic objects in beach sediments, in order to develop an efficient analytical protocol to extract MPs from sediments.”

 Response: We thank the reviewer for the effort in reviewing the manuscript. Responses to specific comments are listed below (please note that line numbers refer to the “marked changes” version of the manuscript).

 

My first major concern is that this study only provided adequate data to address the first aim, but not the second and third aims.

 Response: We thank the reviewer for this comment, and we agree that (especially without a characterization of MPs, see following response below) a clear reconstruction of secondary microplastic composition is not completely feasible. However, through the characterization of plastic litter, FTIR analyses and considering the environmental factors affecting plastic sourcing and transport in the study area, we successfully recognized the main issues affecting plastic transport and deposition on the shores (i.e., main winds and direct littering), as well as the main processes affecting plastic ageing and biofouling (observable from the FT-IR spectra), confirming the main trends observed in other reports, describing then the main conjectures of secondary MPs composition. We clarified in the manuscript text the potentials and the limits of our approach (in lines 100-105; 276-278; 366-385 and 410-421).

 

My second major concern is that this study did not provide any data of microplastics (MPs). The aims, the findings from larger-sized plastic litter and all discussion should be more carefully interpreted if the authors attempt to link this study to MPs.

 Response: We thank the reviewer for pointing out this issue. We agree that the missing characterization of MPs can be a major hindrance to our discussion and conclusion, which does not permit a validation of the potential sources of MPs. We therefore revised the text accordingly in section 3.4, indicating this limit and listing the main assumptions made regarding the possible MP composition derived from available data.

 

My minor concerns are listed provided.

Line 53: Strictly speaking, biofouling (i.e. accumulation of organisms on surfaces where they are not wanted) is not a process of plastic degradation. Please reword.

 Response: We thank the reviewer for this suggestion. We changed the term “deterioration” with “ageing” (line 55).

 

Line 138: “All detectable plastic litter was collected in plastic bags…” Please comment on the possibility of contamination.

 Response: We thank the reviewer for this comment. However, considering the size of collected litter, we ruled out possible contamination after an evaluation of bag integrity following sampling. This issue was better stated in methos (lines 169-172).

 

Line 144: “Polymeric material such as styrofoam and polyurethan have been classified as building material...” It may be more appropriate to categorise styrofoam as packaging material, instead of building material.

Response: We thank the reviewer for this suggestion, and we revised the text (lines 165-168 and 239-245) and Figure 3 accordingly.

 

Reviewer 3 Report

Comments on the manuscript, What are lake beaches made of? An assessment of plastic beach litter on the shores of Como Bay (Italy), by Bellasi et al.

 

Recent researches have been calling attention to possible effects of microplastics in seafood such as oyster, mussel and fish etc since most of MPs are eventually transported to ocean via rivers The manuscript is an interesting report to quantify the presence of plastic beach litter in the Como Bay, Italy, to tarck potential sources of plastic contamination in freshwater bodies and evaluate their characteristics of secondary MPs. The topic is fundamental and the findings are good for plastic pollution management, but it did not have too much new discovery. I recommend publication in Applied sciences after a moderate revision. Below are specific comments:

 

Introduction: I think the authors tried to (i) identify sources of plastic waste on beaches nearby Como city, (ii) assess the processes causing accumulation and (iii) understand the likely polymeric nature and the grade of degradation of collected plastic objects in beach sediments. The authors mentioned potential sources of MPs in the beach and their policy to process, but the fact is that many papers have reported sources of MPs in different aquatic environments. Currently, people mainly concern how these MPs enter aquatic environments and affect aquatic and marine organisms or animals such as birds, fish and filtered organisms. I suggest the authors should extend their introduction and address that these MPs in natural surroundings have entered aquatic (or marine) food web.  In fact, occurrence of MP in many little fish occurring in many countries (Piyawardhana et al., 2000). These polymers of MPs entering marine food web have been identified, but the mechanism of accumulation in little fish are still poorly understood. Maybe, the authors’s finding for secondary MPs in beach will be eventually transported or carried to open oceans. So, I would suggest that the authors should review MP pollution in this literature and discuss potential MP influence from ’s other current studies. It is important to compare composition and size of their MPs to filtered organisms such as oysters, mussels and different fishes, including references    

 

Piyawardhana et al., (2022) Occurrence of microplastics in commercial marine dried fish in Asian countries. Journal of Hazardous Materials. 423, 127093.

 

In method section, I am curious if the authors measure additives of plastic litter, potentially hazardous chemicals, besides MP in their samples? If so, they need to report it.

In Results and discussion, the authors should discuss their findings of MP polymer to and other freshwater or saltwater fish containing MPs polymer since these surveyed plastic litter will be degraded and fragmented into smaller pieces by UV radiation, oxidation, strong currents, huge waves and microbial process.  . Finally, in the implications for the environmental fate of MPs. I suggest the authors should include few in depth discussions potential factors (flood, strong wind etc.) carrying these secondary MPs entering aquatic environments. As a consequence, these MPs will enter aquatic system and some of them be ingested by zooplankton or other and then be transported to food web and be accumulated in freshwater and/or marine organisms. These MPs may impact aquatic and/or marine ecosystems.  

Author Response

Reviewer 3

Recent researches have been calling attention to possible effects of microplastics in seafood such as oyster, mussel and fish etc since most of MPs are eventually transported to ocean via rivers The manuscript is an interesting report to quantify the presence of plastic beach litter in the Como Bay, Italy, to tarck potential sources of plastic contamination in freshwater bodies and evaluate their characteristics of secondary MPs. The topic is fundamental and the findings are good for plastic pollution management, but it did not have too much new discovery. I recommend publication in Applied sciences after a moderate revision. Below are specific comments:

Response: We thank the reviewer for the time and the efforts in reviewing our manuscript. We agree that this is generally a local study, but we consider different innovative methodologies in understanding litter sources and possible fate of secondary MPs. Responses to specific comments are listed below (please note that line numbers refer to the “marked changes” version of the manuscript).

 

Introduction: I think the authors tried to (i) identify sources of plastic waste on beaches nearby Como city, (ii) assess the processes causing accumulation and (iii) understand the likely polymeric nature and the grade of degradation of collected plastic objects in beach sediments. The authors mentioned potential sources of MPs in the beach and their policy to process, but the fact is that many papers have reported sources of MPs in different aquatic environments. Currently, people mainly concern how these MPs enter aquatic environments and affect aquatic and marine organisms or animals such as birds, fish and filtered organisms. I suggest the authors should extend their introduction and address that these MPs in natural surroundings have entered aquatic (or marine) food web.  In fact, occurrence of MP in many little fish occurring in many countries (Piyawardhana et al., 2000). These polymers of MPs entering marine food web have been identified, but the mechanism of accumulation in little fish are still poorly understood. Maybe, the authors’s finding for secondary MPs in beach will be eventually transported or carried to open oceans. So, I would suggest that the authors should review MP pollution in this literature and discuss potential MP influence from ’s other current studies. It is important to compare composition and size of their MPs to filtered organisms such as oysters, mussels and different fishes, including references    

Piyawardhana et al., (2022) Occurrence of microplastics in commercial marine dried fish in Asian countries. Journal of Hazardous Materials. 423, 127093.

 Response: We thank the reviewer for the consideration. Accordingly, we added a paragraph in the introduction section (lines 64-75) and another in the discussion section (lines 366-385), discussing in more detail the likely cascade effects on the biological systems related to our findings. We also added the suggested reference and others to improve this discussion.

 

In method section, I am curious if the authors measure additives of plastic litter, potentially hazardous chemicals, besides MP in their samples? If so, they need to report it.

Response: We thank the reviewer for the question. However, the main aim of this study was just to observe the main polymeric composition in order to understand potential sources and fates. These chemical features will be possibly applied in future studies to better highlight the possible threats for the lake water ecosystem.

 

In Results and discussion, the authors should discuss their findings of MP polymer to and other freshwater or saltwater fish containing MPs polymer since these surveyed plastic litter will be degraded and fragmented into smaller pieces by UV radiation, oxidation, strong currents, huge waves and microbial process.  Finally, in the implications for the environmental fate of MPs. I suggest the authors should include few in depth discussions potential factors (flood, strong wind etc.) carrying these secondary MPs entering aquatic environments. As a consequence, these MPs will enter aquatic system and some of them be ingested by zooplankton or other and then be transported to food web and be accumulated in freshwater and/or marine organisms. These MPs may impact aquatic and/or marine ecosystems.  

Response: We thank the reviewer for this consideration. As already stated in the previous comments, we enriched the discussion better improving the likely effect of secondary MPs on this ecosystem. We also added different possible environmental implication related with plastic oxidation, mechanical degradation and biofouling (lines 275-278, 299-303 and 376-385).