Mercury Contamination: A Growing Threat to Riverine and Urban Communities in the Brazilian Amazon

Round 1

Reviewer 1 Report

This study evaluated human Hg exposure in urban and riverine areas impacted by artisanal small-scale gold mining. It also assessed liver and kidney marker levels which maybe affected by Hg exposure. Generally, it was well designed and the results are interesting. The sampling size are big enough and it was valuable for these human blood samples. However, the big problem is that the health effects were not accurately evaluated by the biochemical analysis. As we know, MeHg is toxic especially for nervous system and generally we focus on biochemical analysis of neurotransmitter and oxidative damage. For IHg, we focus on renal effect and the most commonly used indicators include serum creatinine (SCr), uric acid, blood urea nitrogen (BUN), cystatin C, beta-2 microglobulin, etc. Therefore, the biochemical markers of glucose (non-fasting), urea, and creatinine (for kidney function), alanine aminotransferase (AST), and aspartate aminotransferase (ALT) (for liver function) should be re-considered. For these five biomarkers, we did not find significant difference between residents from urban and riverine areas and between low and high Hg exposure level. I think it maybe the residents from urban riverine areas also indicated Hg exposure and other control sites should be considered. I think that this paper needs major revision before acceptance in IJERPH.

Specific comments:

1. Quality Control. The results of the CRMs should be listed in the paper.

2. Fish consumption is the most important factor for blood Hg level. But the analysis in Table 2 is not well designed. The fish consumption style can be more quantitative and then discuss the relationship with blood Hg level.

3. There are lot of studies of human Hg exposure in the Amazon River. The authors should compare the data with previous studies.

4. The section of Conclusions should be re-organized.

Author Response

Dear Reviewers,

 

Thank you very much for your thoughtful and detailed responses. We have carefully read through each of your comments and provided as specific and detailed responses as possible. Your suggestions were extremely valuable in reshaping and strengthening our manuscript. In the section below, you will see our detailed responses to each of your comments and explain why and how we have addressed each comment.

 

 

Reviewers´ comments:

Author Response File: Author Response.pdf

Reviewer 2 Report

To the authors,

　This paper clarifies that the authors assessed and compared blood Hg levels in individuals living in urban and riverine areas in the lower Tapajós basin and examined the association between Hg exposure and specific biochemical parameters. The content has its priority and importance and is at a level that can be sufficiently posted.

Minor revision

Line 23   (57,1%)⇒（57.1%)

Line 118-119   World Health Organization⇒World Health Organization (WHO)

Author Response

Dear Reviewers,

 

Thank you very much for your thoughtful and detailed responses. We have carefully read through each of your comments and provided as specific and detailed responses as possible. Your suggestions were extremely valuable in reshaping and strengthening our manuscript. In the section below, you will see our detailed responses to each of your comments and explain why and how we have addressed each comment.

 

 

Reviewers´ comments:

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper documents Hg exposure of inhabitants of the Tapajos river basin, Brazil, arising mainly from the widespread practice of artisanal gold mining. The subject is not new, having been covered in a number of papers, including a couple of recent ones by the same group, and a 2015 paper specifically dealing with the city of Santarém. This study expands the database, and in this sense may be useful. However, it is essentially descriptive, and does not add much new insight. The experimental design, and therefore the impact of the presented data, suffers from serious limitations (see below); discussion should be strenghtened. To the extent of my knowledge the language appears correct (see however a few suggestions in the attached pdf).

Specific comments

1. It is unclear how were the individuals selected (voluntary? random choice? why were indigenous excluded?). How do you know the selection is representative of the population at large? A serious limitation is the failure of ascertaining any involvement of the subjects in ASGM. This obviously confounds "professional" exposure with ambient and dietary exposure.
2. The use of other indicators (urinary and hair Hg content) would have strengthened the hypothetical relationship to dietary habits, and made more significant the comparison with previous studies (see next point).
3. Discussion should be more incisive, including a comparison between results of this study and previous ones on mercury exposure in the Amazon and the city of Santarém: which are the new findings compared to previous studies, and what new insight do they provide with respect to the studied phenomena?
4. Conclusions should summarize the results obtained in this study, and not introduce further arguments and citations. The first paragraph pertains to Discussion, and the second to Introduction
5. See additional comments on specific points in the attached pdf (lines 114,152,253-257,281)

Comments for author File: Comments.pdf

Author Response

Dear Reviewers,

 

Thank you very much for your thoughtful and detailed responses. We have carefully read through each of your comments and provided as specific and detailed responses as possible. Your suggestions were extremely valuable in reshaping and strengthening our manuscript. In the section below, you will see our detailed responses to each of your comments and explain why and how we have addressed each comment.

 

 

Reviewers´ comments:

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors addressed all the raised questions and I think it can be accepted in this form.

Author Response

Many thanks for your previous comments that have helped to improve the manuscript.

Reviewer 3 Report

The authors should improve some general aspects:

1. I can easily understand the reasons for selecting on a voluntary basis the individuals for the study. However, this criterion does not guarantee representativity for the overall population. Therefore, the meaning of comparisons/extrapolations is limited to the specific group, and cannot be assumed as a general trend - you should comment on this aspect. 
2. The Discussion does not include a comparison with results of previous studies. The added paragraph (lines 273-284) explains the different approach compared to previous studies, and belongs to Introduction. You say that comparison is made in lines 318-330, but this is not apparent.
3. You should try to strengthen the Conclusions, that at present are rather thin
4. See a few other comments in the pdf

Comments for author File: Comments.pdf

Author Response

Please see the attachment

Author Response File: Author Response.docx