Impact of indoor air pollution in nursery and primary schools on childhood asthma
Graphical abstract
Introduction
Air pollution has been associated with several adverse human health outcomes, namely respiratory symptoms and chronic diseases like asthma (Goldizen et al., 2016; Götschi et al., 2008; Norbäck et al., 2018; Norback et al., 2019; Thurston et al., 2017). Those associations were extensively documented for ambient air (Day et al., 2017; Khreis et al., 2017; Tsui et al., 2018), nevertheless, people spend most of their time in indoor environments. Due to their physical constitution and breathing pattern, children are more susceptible to the health effects of air pollution than adults, being considered a frail population (Annesi-Maesano et al., 2003). While the impacts of home environment on childhood asthma have been extensively studied (Breysse et al., 2010; Cui et al., 2020; Ferrero et al., 2017; He et al., 2020; Huang et al., 2020), the school was usually less studied although it is the most important indoor environment for children apart from home, as well as their first place for social activity. Besides, children are frequently physically active in school, increasing their ventilation rate and thus the inhaled dose of pollutant concentrations. School building characteristics have a significant contribution to indoor air exposure (Amato et al., 2014; Salonen et al., 2019), and building maintenance is usually challenging in schools (Hauptman and Phipatanakul, 2015; Sá et al., 2017).
Poor indoor air quality (IAQ) in schools has been often reported and related to: i) respiratory disturbances, namely affecting nasal patency (Simoni et al., 2010); ii) increased prevalence of clinical manifestations of asthma and rhinitis, with a higher risk for children with a background of allergies (Annesi-Maesano et al., 2012); and iii) wheezing and lung function abnormality in pre-schoolers, especially related with exposures to particulate matter, total volatile organic compounds (TVOC) and carbon monoxide (CO) (Rawi et al., 2015). Although poor IAQ in scholar environments have been frequently reported, relationships between IAQ in schools and the allergic and respiratory health of schoolchildren have been insufficiently explored (Annesi-Maesano et al., 2013; Annesi-Maesano et al., 2012; Patelarou et al., 2015). Moreover, published studies regarding the relationship between IAQ in schools and children's allergies and respiratory health, in particular childhood asthma, usually presented at least one of following gaps: i) focusing only on urban areas, neglecting rural sites where both children's time-activity-patterns and outdoor air concentrations are expected to differ; ii) classrooms' concentrations were usually assumed as exposure, not considering children's time-location patterns and neglecting other relevant indoor microenvironments (canteens, bedrooms); iii) inhalation exposure models were commonly used, although they did not strictly take into account the inhaled dose of airborne compounds, but only the presence of air pollutants near the breathing zone of a person; iv) considering single or few pollutants individually, neglecting their combined effects; and v) respiratory health data, especially asthma-related, is usually parent-reported in a survey, instead of measured and confirmed by a physician.
Thus, by following INAIRCHILD project (Sousa et al., 2012a) and its previous results (Branco et al., 2020; Branco et al., 2019) and to fulfil the gaps in the existing literature, this study mainly aimed to evaluate the associations between children's exposure/inhaled dose to indoor air pollutants and childhood asthma in nursery and primary schools. This study goes further on the literature because it: i) considered both urban and rural sites and included children from two different age groups (pre- and primary school children); ii) used a microenvironmental modelling approach to estimate indoor air pollutants' exposures and inhaled doses, considering classrooms, but also other different indoor scholar environments; iii) analysed several major indoor air pollutants, individually and combined; and iv) diagnosed asthma based on medical doctors' physical examinations according to the most recent guidelines. Two complementary hypotheses were tested: i) if exposures/inhaled doses of indoor air pollutants in nursery and primary schools are associated with childhood asthma prevalence, reported respiratory symptoms and/or changes in lung function; and ii) if children's sensitisation (to the most common aeroallergens) influence on that association, i.e., associations between indoor air pollutants exposures/inhaled doses and childhood asthma differences among sensitised and non-sensitised children.
Section snippets
Study population and health assessment
This cross-sectional study involved children randomly recruited from the nursery and primary schools (urban and rural) participating in the INAIRCHILD project in the academic year of 2013/2014 (campaign 1) and 2015/2016 (campaign 2, to increase sample size), including pre-schoolers (3–5 years old) and primary school children (6–10 years old) but excluding infants (under 3 years old). Those nursery and primary schools were located in both urban and rural sites in northern Portugal (41°N, 8°W),
Characterisation of the study population and health outcomes' prevalence
With a participation rate of approximately 39%, this study involved 1530 children attending nursery (648 pre-schoolers) and primary schools (882 primary school children), both from urban (59.8%) and rural areas (40.2%). Children were randomly recruited from nursery and primary schools (both urban and rural), and no inclusion/exclusion criteria were used, to avoid potential selection bias. Mean age (SD) of this study population was 6.0 (2.1) years old, with 4.0 (0.9) years old in pre-schoolers
Discussion
This study added new findings to the state-of-the-art. In the present study, exposures were strongly correlated with inhaled doses in all the studied pollutants, and similar results were also obtained from exposure and inhaled dose models of association, although inhalation exposure models do not strictly take into account the inhaled dose of compounds, thus neglecting inhalation rates and the bodyweight of the individuals.
Despite covering most of the relevant indoor air pollutants, this study
Conclusions
This study represented the complex mixture of several air pollutants that occur in indoor air by considering multipollutant models of association. Nevertheless, and although this study covered most of the considered major indoor air pollutants of nursery and primary schools environments, overall it found no evidence of a significant association with the prevalence of childhood asthma. However, other asthma-related outcomes were associated with children's exposure to IAP in nursery and primary
CRediT authorship contribution statement
Pedro T.B.S. Branco: Investigation, Formal analysis, Software, Data curation, Writing - original draft. Maria C.M. Alvim-Ferraz: Methodology, Writing - review & editing. Fernando G. Martins: Methodology, Writing - review & editing. Catarina Ferraz: Investigation, Validation, Writing - review & editing. Luísa G. Vaz: Investigation, Validation, Writing - review & editing. Sofia I.V. Sousa: Conceptualization, Methodology, Supervision, Writing - review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors are grateful to the children and their parents/caregivers, as well as to the governance bodies and staff of all the nursery and primary schools' involved in this study. This work was financially supported by: Base Funding - UIDB/00511/2020 of the Laboratory for Process Engineering, Environment, Biotechnology and Energy – LEPABE - funded by national funds through the FCT/MCTES (PIDDAC); project PTDC/EAM-AMB/32391/2017 funded by FEDER funds through COMPETE2020 – Programa Operacional
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