PONE-D-20-37412

Effects of indoor air pollution due to solid fuel combustion on physical growth of children under 5

PLOS ONE

Dear Dr. Ranathunga,

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PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: I Don't Know

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: No

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Dec-10-2020

Comments to the manuscript PONE-D-20-37412:

In the present manuscript, the authors used a population-based descriptive cross sectional study to address the association between solid fuel combustion-derived indoor air pollution and the physical growth in children less than five years old in Ragama MOH, Sri Lanka. The exposure was defined by cooking fuel types and pollutant levels were measured in a household subsample. They reported that the high-exposure children had significantly lower mean z-scores for weight-for-height, height-for-age and weight-for-age, and the scores were negatively correlated with indoor CO and PM2.5 concentrations related to cooking. They concluded that indoor air pollution by biomass fuel combustion leads to poor physical growth. The study is of significance; however, there are methodological concerns about the research as presented.

1. Indoor air pollution is strongly spatiotemporally dependent. A child may be hurt more severely by indoor air pollution as the cooking lasts longer even if the pollution is comparable or lighter. Analysis with the absence of exposure time will, therefore, compromise the results.

2. In the high-exposure group, unprocessed biomass, which includes wood, grasses, crop residues or animal dung, was used for cooking. Coal and kerosene were also used. In the low-exposure group, they used liquefied petroleum gas or electricity, with the former producing particles, SO2, NOx, CO, non-methane total hydrocarbons (incomplete combustion), etc., at a lesser extent. Since different fuel combustion produces different air pollutants, which may exert different harmful effects on health, the authors need to present in detail the situation of households using different fuels. Besides, they should pay attention to the history of fuels used, because the type of fuels might be changed during the study period.

3. Air quality was measured in 115 out of 242 households. Why were the measurements not taken from all households? Similarly, analysis was performed based on data from the subgroups (e.g., Table 7). Comparisons conducted with smaller sample sizes would potentially bias the results.

4. Inclusion and exclusion criteria were not presented. Was the child with premature birth, obesity or other abnormal conditions (prenatally and postnatally) included? Are there any twins?

5. Description for data analysis is not sufficient. How to compare the anthropometric parameters, e.g., values of weight-for-age z-scores expressed as mean and SD (Table 03), between the two groups? There is a lack of description regarding confounding factors in Method session. The authors should give the reason why they chose exposure status, age, sex, monthly family income and parental education as the confounders. Multicollinearity should be considered for tightly correlated variables if any. Did they consider the co-effects of outdoor-level air pollution, which may not be negligible especially in developing countries?

6. There are strong relationships of different toxic pollutants to one another with regard to air pollution on health. There are no models of multi-pollutants to reflect the texture of air pollutants. The average concentrations of CO, CO2 and PM2.5 for both groups should be given. What did the authors evaluate the temperature and humidity for?

7. The authors may have to evaluate the weakness of the study in the Discussion session.

8. Other points:

(1) “Any detrimental effect on growth during early childhood is irreversible” (Line 51): This may not be true because some effects are temporary and reversible.

(2) form → from (Line 92).

(3) ‘exposed group’ (Line 96) and “control group (Line 97): It is more appropriate to use “high exposure group” and “low exposure group”, as used by the authors in other places.

(4) Statements such as “… to collect socio-demographic data and the principal source of cooking” (Line 102) should go to the Method session.

(5) “PM2.5 and Carbon Monoxide (CO) concentrations were measured …” (Line 144-145): It should be PM2.5, CO2 and CO to be measured.

(6) I suggest the sublevel headings be used for the Results session.

(7) “Stunting and wasting were …” (Line 200-201)：→ The prevalence (or ratio) of stunting and wasting was…

(8) “P” whether in uppercase (as in Table 3) or in lowercase (as in Table 2) should be consistent.

(9): Table 1 (Page 9): “Family income” : Is it monthly income ? (indicated in Line 242)

(10): “Entire study population” column in Table 2 (Page 10): “n = 1.7” ?

(11): Line 213 and 214: “vs” → “vs.”.

(12): Line 235: “… to children three …”→ “… to children of three …”; “(Tables 4 and 6)” → (Tables 4-6).

(13): Line 306-308: Lacking reference(s).

(14): “the findings of a study amongst older children may be different”: No supportive data.

(15): “However, as households with higher IAP … , IAP would contribute … on physical growth” (Line 327-330): The authors give insufficient rationales that IAP contributed significantly because IAP is not definitely correlated with other adverse conditions.

(16): Line 336: “mg/m3” → μg/m3

(17): “respirable particulate matter” (Line 341): Do they refer to “inhalable particulate matter”? If so, “PM2.5” that follows can be omitted.

(18): I suggest the name of country be added in the title and deleted in “Key Words”.

(19): Line 371-373: Since it is not necessary to repeat the funding, the Acknowledgements session can be deleted.

Reviewer #2: This is an important study on the health impact of indoor air pollution on child growth. On the whole, the study is designed appropriately, the data collected with adequate care, and the manuscript well written. My main comments concern the choices that the authors have made in their analysis, presentation, and write-up.

1. As this is an observational study, the authors may wish to change the title to reflect that appropriately.

2. The supplementary information is another article on the effect of indoor air pollution on childhood respiratory diseases published by the authors. Is this intentional or a mistake?

3. The choice of covariates in the regression is not clear to me. Why did the authors not use all the covariates in the regression analysis?

4. The results in tables 4-6 can probably be presented more succinctly (in one table).

5. Did the authors run regressions with the quantitative measures of air pollutants as the independent variable(s) rather than exposure group? I would be interested in seeing the results for these regressions as well.

6. The manuscript does not interpret the regression estimates comprehensively (sign, significance and size). The size of the effect should probably be described in the results section.

7. In the discussion, the authors refer to the results of the correlation between severe anthropometric failure and exposure group after discussing the results of the regressions. If the authors wish to establish the (absence of a) relationship between severe anthropometric failure and exposure group, they might want to run regressions with severe stunting, severe wasting, and severe underweight as the dependent variable.

8. The limitations of the study should be described in the discussion.

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Reviewer #1: No

Reviewer #2: No

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Effects of indoor air pollution due to solid fuel combustion on physical growth of children under 5 in Sri Lanka: A descriptive cross sectional study

PONE-D-20-37412R1

Dear Dr. Ranathunga,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Qinghua Sun, MD, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Comments to the revised version of the manuscript (No. PONE-D-20-37412R1):

The authors have answered all the questions well and revised what necessary in the text, including the addition of “Limitations” statement. With the addition of exclusion criteria, i.e., “Children with any diagnosed chronic illness, born prematurely (before 36 weeks of gestational age), with congenital abnormalities or having a recorded history of birth insults were excluded” (P.99-102), it is anticipated that there might be a few children who met the criteria to be excluded. I wonder why none of the children was ruled out. The authors may need to check the data carefully.

Some minor points:

1. “Data were entered … using SPSS version 16 software” (L.159 in “Data Analysis”) and “All analyses were done using SPSS version 20” (L.168): Which version is right?

2. “databaseand” → database and (L.158)

“software.Categorical” → software. Categorical (L.159)

“Ethicsconsiderations” → Ethics considerations (L.169)

“wereusing” (L.185) → were using

“whogenerally” (L.354) → who generally

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No