Review Reports - Occupational Exposure Profiles and Respiratory Health Outcomes Among Surface and Underground Miners: A Comparative Epidemiological Analysis

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper investigates the health effects of exposure to dust and other substances among underground coal miners, using work location (surface or underground) as a proxy for exposure. Although exposure levels were not measured directly, this study is considered important as it provides valuable information for the health management of coal miners and for understanding the health effects of exposure to dust and other substances.

On the other hand, the reviewer could not fully grasp the working conditions in this mining context, so the reviewer would like to ask the authors to clarify these conditions to better understand the value of this study. While the results may be reasonable, the information provided to support them is insufficient for reviewers and readers to fully understand the background context of the relationship between exposure and health effects.

Please revise the paper appropriately based on the following comments so that reviewers and readers can understand the details and significance of this study.

Line 96: I believe the key point of this paper is whether workers are employed on the surface or underground. However, as a fundamental question, what kind of people work on the surface or underground, and why? If there are specific reasons why workers are assigned to one location or the other, I believe it is necessary to indicate how these factors are taken into account in this study; however, I do not see any such sections. Please clarify this point before proceeding with the manuscript. Additionally, please include basic information regarding the work environments on the surface and underground—such as ventilation conditions and job duties—to the best of the author’s knowledge. The reviewer believes this information is essential for understanding whether the comparison is valid.

Lines 113–119: What is the null hypothesis in this paper? The reviewer had assumed the aim was to investigate differences in health effects between surface and underground work, but the sample size calculation was based on a different hypothesis. It is unclear why a 50% prevalence was assumed. Please confirm what the appropriate null hypothesis for this study is and what kind of sample size calculation needs to be performed.

Lines 123–124: What does “incomplete data on key exposure or outcome variables” refer to? The reviewer did not understand what this meant. Please clarify this point.

Line 80: Do workers at both surface and underground work sites know about the working conditions and hours at the other site? Or are they working without knowing these details? Also, do they work at the same work site throughout, or do some people change work sites? Please provide basic information regarding work in this mine.

Line 194: This is a simple question from the reviewer: the authors used Epi Info for sample size calculations and STATA for statistical analysis. While the reviewer believes it is possible to perform all calculations using just one of these software programs, please explain if there is a specific reason for dividing the calculations between different software.

Table 1: This may be a follow-up to Comment No. 4, but it appears that workers employed in surface mining tend to have shorter tenure than those in underground mining. Is there a specific rule for determining the mining type? The reviewer believes that mining type is considered the most important factor in this paper; however, due to the lack of information regarding the method or rationale for selecting mining types, it is difficult—or rather, impossible—to evaluate the paper properly. I understand that you can only write based on what you know, but since this information is necessary for evaluating the paper, please provide a more thorough and detailed explanation.

Table 2: Regarding the dust exposure level, are respondents merely providing their personal impressions? If they have experience with or knowledge of both mining types, it is possible that they are providing a somewhat objective assessment. However, if they lack knowledge of the other mining type, it becomes unclear how to interpret the dust exposure level results.

Table 2: Who decides on the use of PPE? Is it the workers themselves, or is it site supervisors, etc.?

Table 3: This is a minor point, but a closing parenthesis “)” remains in the “wheezing” column. Please remove it.

Table 4: You state that this table shows results regarding chronic cough, but the term “symptoms” is in the plural form. The reviewer believes you should either change it to the singular form to explicitly indicate that the results pertain to chronic cough, or add a reference to other respiratory symptoms. The same applies to Table 5.

Lines 445–451: As noted in previous comments, the reviewer believes the description of the exposure conditions is somewhat insufficient. Consequently, this paragraph gives the impression of being overstated. It would be more appropriate to describe the exposure conditions in greater detail or, at the very least, to delete this paragraph.

Author Response

Greetings,

Thank you very much for the constructive comments and valuable recommendations provided to improve the quality of this manuscript. We have carefully considered all reviewer comments and devoted considerable effort to addressing each concern to the best of our scholarly ability. We believe that the revisions have substantially strengthened the manuscript in terms of its clarity, methodological rigor, and overall contribution to the field.

A detailed, point-by-point response to all comments is provided below, indicating how each issue was addressed in the revised manuscript.

We sincerely appreciate the time, expertise, and thoughtful feedback provided by the reviewers and editor, which have greatly assisted us in improving the quality of this work.

Kind regards,

Authors

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Manuscript ID-ijerph-4300005

This manuscript (MS) report occupational exposure profiles and respiratory health outcomes among surface and underground miners: a comparative epidemiological analysis.

This is an important and relevant topic for both indoor air quality and occupational health. However, the manuscript still has several key issues, particularly in how the study design is explained, inconsistencies in the results, interpretation of statistical findings, the exposure and epidemiological analysis approach, and overall clarity of writing, that make it difficult to fully trust the conclusions at this stage. Substantial revision is required before the manuscript can be considered for publication.

Comments and Suggestions

1.Study design and sampling scheme

The manuscript states that miners were monitored; however, the basis for sample selection is not sufficiently explained. The authors should clearly state whether the surface and underground miners were selected randomly, non-randomly, or through voluntary participation, and should discuss the potential selection bias resulting from the sampling strategy.

In addition, the occupational exposure data and health risk assessment presented in the manuscript are based on working durations of ≤8 hours or >8 hours. However, in the “Questionnaire Development and Data Collection” section, the exposure duration period is described too broadly (Line 140) and does not clearly correspond to the actual exposure duration. The authors are advised to include “ever smoked” as a category in the smoking status variable for the health risk assessment. What is the ventilation system referred to in mining?

2.Occupational Exposure Profiles by Mining Type

Occupational exposure profiles are a core component of this study; however, there are considerable uncertainties regarding the occupational exposure characteristics of mine workers. The exposure profile results reported in the Abstract and Results sections are inconsistent. For example, the Abstract reports the percentages of underground and surface mining exposure (44.9% vs. 24.1%), whereas the Results section states that underground miners were exposed to high dust levels, including corresponding frequencies and percentages. This represents a clear contradiction. The authors are strongly advised to redefine the categories of low, moderate, and high exposure and to provide a complete description of the measurement procedures, criteria, and relevant assumptions in the revised manuscript.

3.Statistical analysis

The manuscript repeatedly describes p < 0.05 as indicating a significant difference. However, some results report p < 0.001. This issue directly affects the interpretation of the results and the credibility of the conclusions. The authors should report all statistical results accurately and consistently throughout the manuscript.

4.Other issues

There are several formatting and language issues in the manuscript that affect readability and professionalism. For example, the word “dust” appears split across different lines, and some lines containing particulate matter descriptions are confusing.

The reference list also requires careful review. For instance, there appear to be inconsistencies between the in-text citation numbers and the reference list, and some reference numbers seem to be duplicated or missing. The authors should reorganize all references according to the journal’s formatting guidelines and ensure that every in-text citation corresponds accurately to an entry in the reference list.

Author Response

Greetings,

A detailed, point-by-point response to all comments is provided below, indicating how each issue was addressed in the revised manuscript.

We sincerely appreciate the time, expertise, and thoughtful feedback provided by the reviewers and editor, which have greatly assisted us in improving the quality of this work.

Kind regards,

Authors

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This study found that underground miners had significantly worse occupational exposure and respiratory health outcomes than surface miners through a comparative analysis of 239 miners in Mpumalanga Province, South Africa. Specifically, underground miners showed a higher proportion of exposure to high dust levels, poor ventilation, and longer working hours, as well as lower consistency in the use of personal protective equipment. Correspondingly, underground miners had significantly higher prevalence rates of chronic cough, shortness of breath, wheezing, and diagnosed lung diseases compared to surface miners. Multivariate regression analysis showed that underground mining type, high dust exposure, and smoking were independent risk factors for chronic cough, with a significant synergistic interaction between smoking and underground mining, indicating that combined exposure to both significantly increases the risk of respiratory system damage.

Convert Table 2, Table 3, and Table 6 from tabular form into grouped bar charts.

Table 2 currently lists four indicators: High dust exposure, Poor ventilation, >8 working hours, and Inconsistent PPE use, with percentages for surface and underground miners. After converting to grouped bar charts, the contrast between groups becomes immediately obvious.

Table 3 lists four health outcome indicators: Chronic cough, Shortness of breath, Wheezing, and Diagnosed lung disease. Grouped bar charts will most intuitively show that underground miners have significantly higher prevalence rates for all respiratory symptoms and diseases than surface miners.

Table 6 presents particularly meaningful and even somewhat counterintuitive findings: underground miners in high-risk environments have lower levels of occupational disease knowledge and protective practices.

The text mentions STATA version 20, but this version does not exist. Please revise to an existing version.
The methods section claims the use of and workplace exposure assessment framework, but all exposure data (dust, ventilation, PPE) actually come from workers' self-reports. Therefore, delete and workplace exposure assessment framework and clearly state that all exposure variables are based on participants' self-reports.
There is a logical contradiction in the variable selection criteria. Both p < 0.20 and based on prior knowledge are mentioned, but it is not explained how conflicts between the two are resolved (e.g., age and gender having p > 0.20 in univariate analysis). Clarify that known confounding factors (age, gender, smoking, etc.) were forced into the model, while other variables were included based on p < 0.20.
All key variables come from the same source (workers' self-reports), which may artificially inflate the strength of the association between exposure and outcome. The methods section does not mention any control measures. Describe control measures in the methods section and discuss this issue in detail in the limitations section.
The discussion of limitations is inadequate. Only cross-sectional design and self-reported symptoms are mentioned, but the following key limitations are omitted:

Common method bias

Unmeasured confounding factors

Sample representativeness (only two mines; can they represent the entire region?)

All literature cited in the discussion should be supplemented with at least 1–2 comparisons with studies from other countries, different types of mines, or different time periods.
When calculating the sample size, a 50% exposure prevalence rate was assumed (to maximize sample size), which is a conservative approach. However, the expected minimum detectable effect size was not explained. Please add this information.
Clearly state in the methods section that the data are self-reported. Supplement the limitations section with the following three points: recall bias and common method bias, the possibility of awareness bias, and lack of objective exposure measurement data

Author Response

Greetings,

A detailed, point-by-point response to all comments is provided below, indicating how each issue was addressed in the revised manuscript.

We sincerely appreciate the time, expertise, and thoughtful feedback provided by the reviewers and editor, which have greatly assisted us in improving the quality of this work.