Recycling of Post-Consumer Polystyrene Packaging Waste into New Food Packaging Applications—Part 3: Initial Contamination Levels in Washed Flakes from Europe
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript by Guazzotti and Welle is very well-written and brings relevant information regarding the contamination levels found in rPS flake in Europe. I have a few comments and suggestions below that I believe would improve the manuscript before it can be accepted to publication.
0) Title/Abstract
Title: I recommend adding in the title that the flakes are “from Europe”, to emphasize that only European PS feedstock was analyzed in the study and it might not be applicable to the United States, for example.
Line 19: Missing a comma after “Based on the data”.
1) Introduction
Lines 49-50: “… can take up to around seven years.” Is a bit informal and I suggest rewriting it.
General comment on the introduction: I would like to suggest to the authors to comment in this section about the regulation on other countries regarding recycled polystyrene for food-contact applications. How does it compare to the European regulations? The main example would be in the United States and the “FDA NOL framework”, where there are currently several NOLs for polystyrene. Also, is there any concern with heavy metal contamination (e.g., Pb, Cd, Cr, etc.) that could be associated with inks, a different country with different regulations, or misuse?
2) Results
Lines 137-138: Was there a significant variability in the number of flakes per 1.0 g subsample within different countries?
Figure 1: It seems that the (a) and (b) are flipped or I do not understand why having Figure 1b coming before Figure 1a. Please check also the figure resolution, as the axis are difficult to read.
3) Discussion
Lines 262-264: Could the data divided by country or location be available in the appendix section in order to support the statement? The samples origin is highly skewed towards Germany, France and Switzerland (38 out of 49 samples).
Line 329: Missing a comma after “In addition”
Figure 2: I suggest using black for the text in the figure. Missing “at” in the legend for the two last conditions (blue and green).
4) Materials & Methods
Lines 362-367: I recommend creating a figure (maybe a pie chart) to illustrate the number of samples per countries.
Section 4.1:
- Was the flake size distribution measured for the samples analyzed?
- It is not clear the type of washing that the rPS flakes received such as cold-wash, hot-wash, etc. Would you be able to expand on that here for clarity?
- Please include details (grade, manufacturer, density, etc.) regarding the virgin PS resins utilized in the study.
Funding/Acknowledgments: In the funding statement, it says the research received no external funding but in the acknowledgement statement, it says the study was financially supported by SCS. Shouldn’t this information be reported in the funding statement (Line 447)?
Author Response
Reviewer 1
The manuscript by Guazzotti and Welle is very well-written and brings relevant information regarding the contamination levels found in rPS flake in Europe. I have a few comments and suggestions below that I believe would improve the manuscript before it can be accepted to publication.
0) Title/Abstract
Title: I recommend adding in the title that the flakes are “from Europe”, to emphasize that only European PS feedstock was analyzed in the study and it might not be applicable to the United States, for example.
Author response: This is indeed an important hint. We have added "from Europe" to the title.
Line 19: Missing a comma after “Based on the data”.
Author response: comma added
1) Introduction
Lines 49-50: “… can take up to around seven years.” Is a bit informal and I suggest rewriting it.
Author response: We have formulated this sentence more precisely.
General comment on the introduction: I would like to suggest to the authors to comment in this section about the regulation on other countries regarding recycled polystyrene for food-contact applications. How does it compare to the European regulations? The main example would be in the United States and the “FDA NOL framework”, where there are currently several NOLs for polystyrene. Also, is there any concern with heavy metal contamination (e.g., Pb, Cd, Cr, etc.) that could be associated with inks, a different country with different regulations, or misuse?
Author response: The manuscript is focused on the European market. Therefore, the US FDA was not discussed. However, we have added two sentences and cited the FDA database and the US Guidence for Industry document. Heavy metal contamination is not addressed neither in the US nor in Europe. Therefore it is not measured within the study. Heavy metals will however be part of the compliance testing according to Regulation 10/2011, which is already mentioned in the manuscript.
2) Results
Lines 137-138: Was there a significant variability in the number of flakes per 1.0 g subsample within different countries?
Author response: We added the sentence: "which indicates that the flake size was relatively homogeneous and showed no significant differences in the different countries or recyclers".
Figure 1: It seems that the (a) and (b) are flipped or I do not understand why having Figure 1b coming before Figure 1a. Please check also the figure resolution, as the axis are difficult to read.
Author response: We switched the two chromatograms.
3) Discussion
Lines 262-264: Could the data divided by country or location be available in the appendix section in order to support the statement? The samples origin is highly skewed towards Germany, France and Switzerland (38 out of 49 samples).
Authors response: There are only a few countries that sort yogurt pots from the packaging waste in sufficient quality for recycling into new packaging. Germany, France and Switzerland are therefore somewhat over-represented. We have included this statement in the manuscript. As the differences between the countries were not significant, we did not break them down by country.
Line 329: Missing a comma after “In addition”
Author response: comma added
Figure 2: I suggest using black for the text in the figure. Missing “at” in the legend for the two last conditions (blue and green).
Author response: We made these changes in Figure 2
4) Materials & Methods
Lines 362-367: I recommend creating a figure (maybe a pie chart) to illustrate the number of samples per countries.
Author response: The number of samples per country are listed in the manuscript. A pie chart would not provide more information. We have therefore not implemented this recommendation.
Section 4.1:
Was the flake size distribution measured for the samples analyzed?
Authors response: We added the flake size
It is not clear the type of washing that the rPS flakes received such as cold-wash, hot-wash, etc. Would you be able to expand on that here for clarity?
Authors response: Hot washing was used for the flakes samples. We included this information into the manuscript.
Please include details (grade, manufacturer, density, etc.) regarding the virgin PS resins utilized in the study.
Authors response: Sheets used for the production of yogurt pots were used as reference materials. These do not consist of just one PS material and cannot be assigned to a polymer manufacturer. Unfortunately, we are therefore unable to provide any information on the grades, manufacturer, density, etc. In our point of view these sheet samples are the more realistic reference samples compared to virgin HIPS pellets. We included this information into the manuscript.
Funding/Acknowledgments: In the funding statement, it says the research received no external funding but in the acknowledgement statement, it says the study was financially supported by SCS. Shouldn’t this information be reported in the funding statement (Line 447)?
Authors response: The results were not produced as part of a public project. Therefore, no external funding was indicated. However, the work was financially supported by the SCS association. This is mentioned in the acknowledgements. To our understanding this is the correct indication.
Reviewer 2 Report
Comments and Suggestions for Authors1. In table 1, what is the meaning of Frequency in the samples? How do you get the data?
2. In some positions, like line 34, 46, 66, the number of references cited is so many. Are all the references involved necessary? It is suggested to simplify the number of literatures cited, and keep the literatures that directly support the conclusion. The author should supplement the recent research results in related research fields.
3. In Figure 1， Is the sequence of "a" and "b" indicated in the figure consistent with (a) and (b) described in the text? Please check carefully.
4. What is the order standard for the compounds in Table 1?
5. The conclusion in the manuscript is suggested to be refined.
6. Some details such as the first abbreviation, language description of the conciseness, the author should carefully modify.
Author Response
Reviewer 2
- In table 1, what is the meaning of Frequency in the samples? How do you get the data?
Authors response: We change in the text frequency of occurrence into frequency of detection of the substances to make this clearer.
- In some positions, like line 34, 46, 66, the number of references cited is so many. Are all the references involved necessary? It is suggested to simplify the number of literatures cited, and keep the literatures that directly support the conclusion. The author should supplement the recent research results in related research fields.
Authors response: The literature on quantitative studies in rPS is not very comprehensive. We have therefore cited the relevant literature. However, the number of citations is manageable compared to other publications. We have therefore not removed any citations from the manuscript.
- In Figure 1， Is the sequence of "a" and "b" indicated in the figure consistent with (a) and (b) described in the text? Please check carefully.
Author response: We switched the two chromatograms.
- What is the order standard for the compounds in Table 1?
Authors response: The substances are listed in the table in order of decreasing highest concentration. This is described more clearly in the manuscript.
- The conclusion in the manuscript is suggested to be refined.
Authors response: This is a very general statement. The conclusions are already very concise and only contain the essential points. In order to revise these, we would need more detailed information on what.
- Some details such as the first abbreviation, language description of the conciseness, the author should carefully modify.
Authors response: This is a very general statement. We have carefully revised the manuscript and paid attention to these points.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have considered most of my suggestions/comments and I recommend the acceptance of the manuscript.
Reviewer 2 Report
Comments and Suggestions for AuthorsPlease check the manuscript carefully to meet the publication requirements.
