Association between the Concentration and the Elemental Composition of Outdoor PM_2.5 and Respiratory Diseases in Schoolchildren: A Multicenter Study in the Mediterranean Area

Round 1

Reviewer 1 Report

Health effects of air pollution, especially in vulnerable sub-populations such as children or the elderly might have huge impact on public health. Thus, the topic of the manuscript is highly relevant and the methods are up-to-date. The manuscript is well written and structured. The limitations of the study are sufficiently discussed at the end of the manuscript. Nevertheless, I have a couple of suggestions that should be included before accepting the manuscript.

General comment:
I’m missing a more complex, multivariate model that should be fitted on the available data. The various markers of air pollution are usually highly correlated and the results given in Table 3 don't account for this correlation. I wondered if the authors could calculate a combined air pollution marker that could be used in the logistic regression models. At least the correlation among the various AP markers should be given. As an alternative approach, a step-wise model could be used to identify the most potent AP marker for asthma.

minor comments:
line 71: differently polluted areas?
line 86: please provide the same information ( inhabitants/km2) for Malta.
line 107: October 6, 2011
line 202: a p value of p=0.051 is not significant. Please be clear with this limits and maybe add some sentences about multiple comparisons!
line 217 (figures 2-5): What exactly its the p-value and why is it heading the figures? It this the main effect? Please give the results of the respective post-hoc tests.
line 231: medication/ drugs against asthma
line 249: was more than twice as high than the prevalence observed amongst …

Author Response

First of all thank you for your comments, which were greatly appreciated and add value to our work. 

 

As regards the general comment, we added figure 7 showing correlation between all the markers.

A good correlation of Ni and V with Pb and Zn was also observed (range 0.5-0.7).     As regards the minor comments: Differently polluted areas was changed to areas with varying levels of pollution.   The population density of Malta was inserted.   October 6, 2011 was corrected.   It was clarified in the text that a p=0.051 was not significant but close to significance when discussing the result.   p values indicated in Figures 2 to 5 are the overall p value computed to Kruskal-Wallis test. Figure legends are now self-explaining. Ad concerns the post-hot comparisons, in results section, at lines 218-221 we say: "The Maltese town of Hamrun had the highest median levels of PM2.5 (Figure 2) and for all the evaluated elements with the exception of Cadmium (highest in Gela) when compared to the rest of the Maltese and Sicilian towns (all p values<0.0001, see Figures 3-5 for Ni, V, and Pb, respectively)"     Drugs against asthma was inserted in the text.   The grammar on "prevalence observed...." was corrected.    Whilst again thanking you for your feedback, I hope that these corrections are satisfactory.   Best Regards,   David Bilocca

Reviewer 2 Report

Atmosphere-1007826

This ms. is very informative, as in outdoor PM2.5 were simultaneously analyzed V, Ni, Cd, Pb, Mn, Sb, and Zn, and their relationship  to respiratory diseases as asthma in school children in Malta and Sicily. Within the first 2 years of life was respiratory illness higher among Sicilian children, but ten years later was asthma more frequent in Malta than in Sicily.

Remarks:

1. 8 l. 233 ORs for rhinitis for Sb - according to Table 3 it is not significant.

Discussion p. 10 l. 274 - concentration of PM2.5 in Hamrun - 20.7 ug/m3, but in Table 2 is 23.6 ug/m3. It should be checked and corrected.

This study is very informative, ms. was very carefully prepared.

It may be accepted after the proposed corrections.

Author Response

Dear reviewer,

 

Many thanks for your comments and positive response to our work. Was greatly appreciate your remarks which help make our manuscript more accurate.

 

We have removed Sb as rightly pointed out this was not significant. We have also corrected the concentration of PM2.5 for Hamrun which now reads correctly in the text as 23.6ug/m3.

 

I hope that you find this correction satisfactory.

 

Best Regards,

 

David Bilocca