Study Results: Please rate your confidence (0 = no confidence/fatal flaw; 5=highest confidence) in the study results generated. Please explain your rating

Answer Explanations

• 2

  Expert 5
  Overall, the interpretation of the results are maintained clarity and presented in a structured and coherent manner, also included statistical measures required. However, analytical issues raised and explained in the previous section 1.1 prevents rating higher confidence in the study results generated. Please see the details 1.1. In addition to this, a small sample size largely reduces the the reliability and generalizability of the findings. Supplementary data are available but not sufficient. 
  
  
• 2

  Expert 4
  The manuscript lacks clear presentation of data/information pertaining to health parameters measured (sperm count, testis weight).  It is expected that authors provide at least weight of testis samples measured/analyzed (mean, range) for both human and canines.  Similarly, some discussion about what is the normal sperm count versus what was found in canines?  Many such critical information is missing/lacking.  Results are not fully reported and are obscure and vague.  
  
  The analytical data for micro- and nano-plastics (MNPs) are questionable due to the lack of method validation parameters.  In other words, analytical method is not clearly described.  There is a clear lack of accuracy and precision information, which is critical in any quantitative analysis of environmental chemicals in biological specimens.  
  
  Very important  and critical information pertaining to sample collection are missing (as mentioned above).  The method just very briefly states how samples were obtained, with lack of information on collection methods, storage conditions, and homogenization protocols.  Samples are a critical part of the work described here but authors have not provided adequate details to understand the reliability of the data presented.
  
  The section on comparison of results of MNPs in dog and human testis, could have benefitted with some discussion about age differences that could have contributed to higher exposures in humans.  Although dogs chew on many plastics, one would normally expect higher exposure in dogs in comparison to humans.  No critical data analysis is made on these aspects.
• 4

  Expert 1
  Except for the points raised in section 1.1, the reviewer has no major issues with the data analysis or the validity of the results. The science of microplastics' impact on human and animal health is evolving, and the researchers have employed state-of-the-art technology and expertise to carry out this research. The results presented are clear, and there are no issues with their accuracy and completeness.
• 1

  Expert 2
  In itself, the authors have reported that results as accurately and fully as possible for them. The paper is clearly written. However, the key issue is that the results are not necessarily accurate and fully reported. Some flaws have already been indicatd in the response to the previous question.
  For me, especially the analytical problems and the lack of validation of the whole 'train' of sampling up till actual anlysis, is an important flaw. Thereupon, there is the issue of all kinds of co-variance between plastics, characteristics of the dogs and humans like origin, age, socio-economic environment, representativity of the samples, etc..
  Finally: given the various factors that potentially affect the endpoints considered here, the number of samples is too low to draw any relevant conclusions. 
• 2

  Expert 3
  Pros
   - Data was explored holistically. 
   - The study has cited relevant literature and the cited studies show that these or similar findings have been reproduced independently in other work already. 
   
  Cons
  - Inconsistency in how the confidence intervals are displayed in Figure 4, some have confidence intervals some don't. The typical convention is that only significant relationships have both while insignificant have one or the other. For some reason only one random plot out of all has a confidence intervals displayed. It also doesn't say in the caption what the confidence intervals range is, presumably 95%. 
  - Another inconsistency is in Figure 3, there is a violin plot for humans but not for dogs. There are similar issues with violin plot inconsistency in presence, color, or shading in Figure 1 and 2. These inconsistencies can mislead readers and lead to inaccurate conclusions about the data. 
  - Supplementary data, supplemental figures, manuscript, and other materials are not openly available, they are behind a paywall so I was not able to assess them.