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

Answer Explanations

• 1

  Expert 5
  1. Small sample size prevents reaching to the reliable concluding remarks;
  2. 'Negative correlations between canine testis weight and concentrations of PVC and PET were observed but did not imply causation'- my evidence based opinion was very clear i.e., analytical methods represents major flaws to conclude this. Also, no explanation why and how it is possible to be negatively correlated. 
  
  
• 1

  Expert 4
  The major conclusions of the study are that MNPs are present in human and dog testis  and a negative correlation existed between canine testis weight and PVC/PET concentrations in testis.  Authors have quantitively assayed the parameters, but the analytical method and sample collection sections are poorly presented and lacks critical data quality assurance and control parameters.  Therefore, analytical data (as a quantitative measure) are questionable.   There is no adequate convincing evidence presented to support the findings.  An additional level of confirmation of the findings using another method of analysis could have enhanced the robustness of conclusions. When an analytical method is not validated for a purpose, it raises concern about any data that emanated from the method.  Discussions are weak and do not present how and why MNPs have reached testis tissues.
  
  Sample size is too small to warrant any association studies (i.e., epidemiology type of data analysis) and no covariates are included or considered in data analysis.  Strength of those conclusions are weak.
• 4

  Expert 1
  The conclusions regarding the higher abundance of microplastics in human testicular tissue compared to canine testicular tissue are well supported by the data. The predominance of polyethylene (PE) over other plastics is also supported by the findings, which align with the higher usage of PE in daily life. It is noteworthy that the authors caution not to come to quick conclusions regarding negative correlations observed in canine testes with respect to PVC and PET. 
  
  
• 0

  Expert 2
  I have very limited confidence in the study conclusions as there are simply too many uncertainties that potentially flaw the conclusions. Too many factors have not been considered whilst the anaytical methodologies (i.e. from sampling until actual analysis) are not sufficiently validated. The conclusions related to correlations between levels of individual plastics and biological endpoints (most notanly: Figure 4) are fully flawed and should not have been published in my opinion.
  Thereupon, there is the issue of insifficient characterisation of the plastics in terms of for instance size, morphology, particle numbers, etc.
• 3

  Expert 3
  Pros
  -  Assuming their results are correct, I think the conclusions are supported by the results and are appropriately qualified based on the limitations of the study design in general. 
  
  Cons
  - I do think the authors should have acknowledged the lack of controls for both blanks and spikes. Without these, there is no telling how much of what they are seeing is from contamination and how much loss they could incur from their method. Matrix effects in PYGCMS are widely known to cause false positives and false negatives and when studying a new matrix like testis, this should be thoroughly vetted. For all we know these results are driven strongly by matrix effects.