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(9 Answers)

The experts are divided on whether additional classification schemes are appropriate for plastic particles in biological tissues. Four experts (1, 3, 5) suggest additional classification criteria, while five experts (2, 4, 6, 7, 8, 9) believe no additional schemes are necessary.

Among those suggesting additional classifications:

  • Size classification was mentioned by Expert 3
  • Degree of weathering was suggested by both Experts 3 and 5, with Expert 5 noting this could indicate environmental exposure and potential contamination with other pollutants
  • Additive content was proposed by Expert 3, though acknowledged as complex
  • Expert 1 highlighted the lack of standardization in classification schemes and suggested measuring particles by mass or weight rather than physical characteristics for biological samples, noting this would be more relevant to risk assessment

Among those satisfied with current schemes, Expert 6 specifically endorsed the importance of morphology (physical impact) and polymer classification (chemical impact) as the most important existing classifications for biological tissues.

Summary Generated by AI

Answer Explanations

  • Yes (please explain)
    Expert 3
    If possible, size classification should be included. Degree of weathering is also a possibility (e.g., carbonyl index). Additive content (though highly complex) is also a possibility. 
  • No
    Expert 9
    I am unaware of classification schemes other than those mentioned in the draft paper.
  • No
    Expert 4
    I think that in principle any existing classification system can be used for plastics in biological tissues provided that the digestion or any other form of pre-processing of the sample, was sufficient to visualize the plastics.
  • Yes (please explain)
    Expert 1
    The classification scheme is still not standardized/harmonized even for environmental samples.  How many types of plastics really are out there?  I have read from stating up to 40 types of plastics.  Are tire wear particles classified as plastics?  A clear listing of the types of MNPs that are currently analyzed/used by researchers need to be presented on this manuscript.

    For biological samples, it is more appropriate to use a methodology that measures them in mass or weight (as ng/g or ug/g) rather than size, shape and color, which have no meaning when it comes to risk.  A recommendation on that regard is needed.  
  • Yes (please explain)
    Expert 5
    If possible to adequately assess, it would be instructive to know the "weathering" of the particles.  MNPs that exhibit "weathering" give a soft measure of the environmental exposure of the particle and thus the possible contamination of other persistent organic pollutants.
    https://doi.org/10.1016/j.watres.2021.117011
    https://doi.org/10.1016/j.envpol.2022.119669
    https://doi.org/10.1021/acsenvironau.2c00036

  • No
    Expert 6
    I think morphology (physical impact) and polymer classification (chemical impact) are most important classification for particles in biological tissues.
1 vote 1 0 votes
Expert 8
07/31/2025 02:40
This is an area where experts diverge significantly. It's intriguing.  Regarding expert 3's answer, carbonyl index can only be used for certain polymers (e.g. polyethylene) and the method for calculating this weathering indicator is not standardized and within consensus across the field. I would caution the authors to include it as a rule, but suggesting the methods need to improve to quantify weathering indicators so that plastic particles can be categorized by weathering severity would be good.
Expert 1 asks about the different types of plastic polymers - there are 1000s of plastic polymers and within each polymer there are 1000s of different grades and additive packages. Particles should absolutely be identified to the polymer chemical structure and reported by polymer category. Tire wear is an interesting and challenging category, since tires are made of a variety of polymer blends and with other polymer reinforcing fibers.  Oof, they are challenging but I agree that tire and road wear particles get their own category because of the abundance in natural environments.
0
Expert 4
07/31/2025 04:52
Looks like there is agreement that such a scheme does not exist. Experts mostly mention issues that need to be part of such a scheme.
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Expert 5
07/31/2025 19:34
I agree with expert 8. There are a multitude on polymer varieties and many variations within a variety. This number becomes unmanageable when additive and modifier formulation differences are factored in.  The authors could address this problem through mentioning annual production output of the 10 - 20 most common polymers as a point of initial focus.
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