Do you recommend any changes to the best practices outlined in Particle Quantification/Qualification sections? If Yes, please explain below and indicate which section you are suggesting changes be made to.

Answer Explanations

• View answer

  Expert 3

  Section	Yes (please explain)	No
  Use standardized morphological, color, and polymer classifications	1	0
  (Sub)samples should contain a minimum of 100 particles per sample, mass detection limits, or the whole sample	0	1
  Use appropriate analytical chemistry techniques	1	0
  Do not overcrowd filters if doing mapping	0	1
  The background for optical, fluorescence, or hyperspectral imaging should be flat and not interfere with the imaging mode	1	0
  Use robust analytical chemistry identification/quantification libraries	1	0

  1) The issue of color is addressed only under an analytical view (spectroscopic analyses), but it should also be emphasized that this classification is important for ecological reasons, for example, as many organisms confuse bright colored particles with food. 
  2) Optical microscopy (though increassingly less used, and with the assistance of dyes) could perhaps be noted. Some more detailed analysis could be added. 
  3) There are some additional alternatives, such as Anodisc. 
  4) Ideally, these libraries should include weathered materials/references.
• View answer

  Expert 9

  Section	Yes (please explain)	No
  Use standardized morphological, color, and polymer classifications	0	1
  (Sub)samples should contain a minimum of 100 particles per sample, mass detection limits, or the whole sample	1	0
  Use appropriate analytical chemistry techniques	0	1
  Do not overcrowd filters if doing mapping	0	1
  The background for optical, fluorescence, or hyperspectral imaging should be flat and not interfere with the imaging mode	0	1
  Use robust analytical chemistry identification/quantification libraries	0	1

  I take issue with the statement that "(Sub)samples should contain a minimum of 100 particles per sample , mass detection limits, or the whole sample", as I do not see how can the number of particles per sample can be known for unknown samples?
• View answer

  Expert 2

  Section	Yes (please explain)	No
  Use standardized morphological, color, and polymer classifications	0	1
  (Sub)samples should contain a minimum of 100 particles per sample, mass detection limits, or the whole sample	1	0
  Use appropriate analytical chemistry techniques	1	0
  Do not overcrowd filters if doing mapping	0	1
  The background for optical, fluorescence, or hyperspectral imaging should be flat and not interfere with the imaging mode	0	1
  Use robust analytical chemistry identification/quantification libraries

  (Sub)samples should contain a minimum of 100 particles per sample, mass detection limits, or the whole sample. YES
  Some additional notes should be added for particular situations where the recovery of 100 particles is not feasible, such as in rare tissue types or early-stage exploratory studies. 
  Use appropriate analytical chemistry techniques. YES
  Consider adding a  table or a visual aid that could indicate for particle size ranges and morphologies the most appropriate analytical techniques that could be used to detect them.
• View answer

  Expert 1

  Section	Yes (please explain)	No
  Use standardized morphological, color, and polymer classifications	1	0
  (Sub)samples should contain a minimum of 100 particles per sample, mass detection limits, or the whole sample	1	0
  Use appropriate analytical chemistry techniques	1	0
  Do not overcrowd filters if doing mapping	1	0
  The background for optical, fluorescence, or hyperspectral imaging should be flat and not interfere with the imaging mode	1	0
  Use robust analytical chemistry identification/quantification libraries	1	0

  One of the major challenges in describing particle type, color and shape is the lack of standardization.  In most cases, this is due to the lack of pure analytical standards.  There is a need for analytical standards of polymers of different types and sizes.  Analytical standards for nanoplastics (nanosized particles) are not currently available expected for a couple of them (PE and PS).  Even when they are available, purity is not enough.  So, in this section, a paragraph may be dedicated about the need for standardization of particle type, shape and color and the need for high purity analytical standards.   
  
  In biological samples, the significance of size and shape of MNPs is less important than mass (weight).  Pyrolysis GCMS methods allow quantification in mass per sample weight.  I think some recommendation related to the need for reporting units is needed  (e.g., # of particles versus ng/g tissue).  
  
  Lines 357-370:  3 studies have been referenced in this section and it reads what those three studies recommended for size, shape and color.  At the end of each subsection, a summary statement or recommendation from author is needed.  Otherwise, it reads like superficially describing few randomly selected  studies without any final remarks.   Some of the recommendations made in this section are OK, but are vague ad superficial. 
  
  The subsection on "(sub)samples should contain.......whole sample".  The wordings used are a bit unclear.  For example, "aliquoting samples can have poor recovery rates" may mean that taking a fraction of sample from an entire organism or an organ can affect recovery.  I do not think this is an accurate statement.  For biological samples, aliquoting is needed, but the main point is the representativeness of the aliquot.  Authors may want to rephrase the statements made on lines 373-375.
  
  Line 385:  Sentence needs rephrasing "The same logic....subsamples".
  
  Line 386-387:  The statement about a minimum of 100 MNPs is somewhat vague.  Where is this number derived from?  Is this from Wagner et al?  Scientific basis for this number/recommendation is lacking.
  
  Line 396:  Plankton splitter is mentioned.  However, this is only applicable for plankton samples and not for other biological tissues.
  
  
  
• View answer

  Expert 4

  Section	Yes (please explain)	No
  Use standardized morphological, color, and polymer classifications	1	0
  (Sub)samples should contain a minimum of 100 particles per sample, mass detection limits, or the whole sample	1	0
  Use appropriate analytical chemistry techniques	0	1
  Do not overcrowd filters if doing mapping	1	0
  The background for optical, fluorescence, or hyperspectral imaging should be flat and not interfere with the imaging mode	0	1
  Use robust analytical chemistry identification/quantification libraries	1	0

  With regard to "Use standardized morphological, color, and polymer classifications" and "(Sub)samples should contain a minimum of 100 particles per sample, mass detection limits, or the whole sample": these sections seem to go beyond the scope of biological matrices. In the case of biological matrices itis not always feasible to do these kinds of assessments and espcially with regard to the issue of 100 particles there is the problem of this information becoming available only after processing of the sample or the subsample. This restriction should be included in the document.
  "Do not overcrowd filters if doing mapping". This section is on a very technical and detailed issue and it is also very brief. Might be good to merge this short section with another one. Also, the topic is not directly linked to the previous and the next section.
  "Use robust analytical chemistry identification/quantification libraries". In itself this section is not providing any novel information as this recommendation is valid for any chemical.
• View answer

  Expert 5

  Section	Yes (please explain)	No
  Use standardized morphological, color, and polymer classifications	0	1
  (Sub)samples should contain a minimum of 100 particles per sample, mass detection limits, or the whole sample	1	0
  Use appropriate analytical chemistry techniques	0	1
  Do not overcrowd filters if doing mapping	0	1
  The background for optical, fluorescence, or hyperspectral imaging should be flat and not interfere with the imaging mode	0	1
  Use robust analytical chemistry identification/quantification libraries	0	1

  100 particles per sample does not apply to PY-GC/MS.  For example, 100 X 100 nanometer particles may not be enough mass for adequate PY-GC/MS (or optical spectroscopy) quantitation. It depends on the polymer type and is pyrolyzation pattern.
  Perhaps add a "100 particles within the limit of detection" qualifier?
• View answer

  Expert 8

  Section	Yes (please explain)	No
  Use standardized morphological, color, and polymer classifications	1	0
  (Sub)samples should contain a minimum of 100 particles per sample, mass detection limits, or the whole sample	0	1
  Use appropriate analytical chemistry techniques	0	1
  Do not overcrowd filters if doing mapping	0	1
  The background for optical, fluorescence, or hyperspectral imaging should be flat and not interfere with the imaging mode	0	1
  Use robust analytical chemistry identification/quantification libraries	1	0

  Line 361-362 "Some classes..." the meaning of this sentence is unclear to me.
  Line 463 Fix verbs since spectra is plural (spectra are... that they are)
  Line 464. Separate this into two sentences.
  Line 468 - I’m doubtful that raw spectra are rarely fit for direct identification. My lab uses the raw spectra more often than not and our library is not transformed or corrected.
  Line 474 - spell out HQI if not already.
• View answer

  Expert 6

  Section	Yes (please explain)	No
  Use standardized morphological, color, and polymer classifications	0	1
  (Sub)samples should contain a minimum of 100 particles per sample, mass detection limits, or the whole sample	0	1
  Use appropriate analytical chemistry techniques	0	1
  Do not overcrowd filters if doing mapping	0	1
  The background for optical, fluorescence, or hyperspectral imaging should be flat and not interfere with the imaging mode	0	1
  Use robust analytical chemistry identification/quantification libraries	1	0

  please also consider the updated libraries and newly developed algorithms, as this is an emerging field and development and optimizing is happening.