Study Discussion: Please rate your confidence (0 = no confidence/fatal flaw; 5=highest confidence) in the study author conclusions. Please explain your rating

Answer Explanations

• 2

  Expert 5
  1. MNPs concentrations and reproductive parameters does not establish causality;
  2. No critical and broader context of toxicological impacts and implications of biological tissues has been discussed such as translocation, fate, accumulation, specifically, how MNPs could translocate and accumulate to biological tissues. 
  3. Explanation about the potential sources of MNPs lacks; absence of physical characteristics shape and size that relates the MNPs exposure discussion; also, how the humans and dogs could potentially encounter, ingest and make the MNPs bioavailable lacks.  
  
  
• 2

  Expert 4
  The manuscript lacks critical and thorough discussion.  Some of the discussions are speculative.  Authors state that concentrations of MNPs in testis may decrease due to continued renewal of sperm during spermatogenesis that could mitigate the buildup of MNPs in testis overtime.  There are many questions with regard to how MNPs are sequestered in testis, such as : Can MNPs cross biological membranes and accumulate in tissues and organs?  Authors would have focused on discussing such aspects of the study to support their findings or provide more supporting evidences from rodent studies.  
  
  
  
• 4

  Expert 1
  The study is predominantly observational. The data obtained from canine tissues is presumably based on freshly harvested samples, whereas the human tissue samples were collected after a 7-year storage period. In addition to this difference in the timeframe, several confounding variables, such as the nature and source of the microplastics, duration of exposure, and the geographic locations, may also be present.
  
  
• 1

  Expert 2
  Actually, the results and discussion sections raised more questions that need to be solved than that this section answers any questions. The uncertainties on the study design and the interpretation of the results are increased in this section, also because the authors themselves add speculative information and they add new limitations.
  Fiurst of all: the first part of the results and discussion (especially the right column of page 2) is simply a repetition of information provided elsewhere and the 'comparative analysis.....' in the mid of this column is repeating the information provided above. The comparison of microplastics found in testes with levels of microplastics in placentas is actually silly, especially since the differences are partly assigned to 'potentially other factors'.
  
  A flaw is that apparently there is a difference in plastics found in private clinics versus public clinics. First of all: thius difference should have been taken into account in the statistical analyses of the data. Secondly, this observation might be due to sample handling, even though it should be noted that this too is purely speculative.
• 3

  Expert 3
  Pros
   - I appreciate how the authors weaved together previous studies to understand their results and advance the current understanding of microplastics on testis. 
  -  I appreciate that the authors used extra caution when discussing these results. 
  
  Cons
  - I feel like there is a good chance that some of the correlations found in the linear relationships are spurious and due to random chance, especially given the fact that they ran so many comparisons and didn't use any multiple comparison correction for their p-value calculation and the findings aren't consistent across the tests in a convincing way. 
  - I'd imagine that the testis-related variables are correlated to one another in some way but this wasn't tested or controlled for.