Cross-sectional associations between ambient air pollution and respiratory signs and symptoms among young children in Tehran
Graphical abstract
Introduction
Air pollution is a global problem and the most important environmental risk factor for human health (Schultz et al., 2017). According to the World Health Organization (WHO) 2016 report, air pollution is affecting all areas of the world, and about seven million people annually lose their lives due to pollution. Approximately 90% of the air breathed by humans does not match the WHO quality guidelines. Epidemiologic evidence and air quality data on the health effects of pollutants are rapidly growing (World Health Organization, 2016). Ambient air pollution has significant effects on bronchitis or symptoms such as cough, phlegm, and asthma and asthmatic symptoms, including wheezing (Hoek et al., 2012). From among different air pollutants, particulate matter (PM) has become a major concern for human health (Ma et al., 2008; Pope III, 2007). Numerous studies have reported the association between PM concentration and increased respiratory symptoms (Ma et al., 2008; Hasunuma et al., 2018; Linares et al., 2010; Hoek et al., 2012) and reduced pulmonary function (Hoek et al., 2012; Roy et al., 2012; Yoda et al., 2018). Many of these studies have investigated PM with an aerodynamic diameter of <10 μm (PM10), indicating that particles are associated with respiratory symptoms and lung function (Ma et al., 2008; Roy et al., 2012; Hoek et al., 2012). Nitrogen dioxide (NO2) is associated with an increase in respiratory symptoms such as asthma exacerbation, wheezing, and bronchitis (Shima and Adachi, 2000). Sulfur dioxide (SO2) also increases respiratory symptoms in susceptible and allergic children and impacts lung function (Dong et al., 2011).
A recent study in 2016 estimated about 41,000 deaths (95% uncertainty interval [UI] 35634, 47014) and about 3,000,000 years of life lost (YLL) (95% UI: 2632101, 3389342) attributable to the long-term exposure to PM2.5 in Iran (SHAMSIPOUR et al., 2019). Tehran, the capital of Iran, is the largest city in the country with a population of about 9 million (Faridi et al., 2018), facing serious air pollution like other large cities (Naddafi et al., 2012). In general, 20% of the total energy in Iran is consumed in Tehran (Naddafi et al., 2012).
From among different age groups, children are more vulnerable to air pollution effects because their lung volume-body ratio is larger and their airway epithelium has a higher permeability to air pollutants (Roy et al., 2012); furthermore, long-term exposure to ambient air pollution can be linked to the incidence of respiratory symptoms and lung function in children (Hoek et al., 2012). According to various studies, the association between ambient air pollutants and respiratory symptoms differs depending on the type of pollutants and respiratory symptoms (Dong et al., 2011; Hwang and Lee, 2010; Gao et al., 2014), which may be due to different sources of air pollutants. Therefore, illumination of the impact of air pollutants on respiratory systems requires more studies in various locations and on different populations. The present study aimed to assess the association between chronic exposure to PM10, PM2.5, NO2, SO2, and CO and children's respiratory symptoms in the megacity of Tehran.
Section snippets
Study area and period
This cross-sectional study was conducted in 2015 on children under the age of seven years in the day-care centers of Tehran.
Selection of day-care centers
To select the day-care centers, a list of Tehran's day-care centers was first prepared and their phone numbers were obtained from Tehran's Welfare Organization. Then, by handing the phone numbers to the Geographic and Spatial Information Office, the geographical coordinates of all the day-care centers were obtained. These coordinates were determined by GIS software on the
Results and discussion
In the present study, 61 out of 121 day-care centers that met the eligibility criteria were included. In these day-care centers, 3639 questionnaires were distributed and 1811 completed questionnaires were collected with a response rate of 49.7%. Since 300 questionnaires were incomplete, the researchers attempted to resolve the deficiencies by telephone interviews, and 200 questionnaires were thus completed and added to the valid questionnaires. As the coordinates of about 44 locations could not
Conclusion
The findings of this study indicated that the daily mean concentration of ambient air pollutants is higher than the limits of WHO air quality guidelines. Also, ambient air pollution is associated with respiratory symptoms, from among which an association is detected between NO2 and SO2 concentrations with current asthma, and CO concentration with persistent phlegm. Moreover, the prevalence of wheezing, bronchitis, and asthma is higher in boys as compared to girls.
CRediT authorship contribution statement
Zahra Namvar: Investigation, Conceptualization, Writing - original draft. Masud Yunesian: Conceptualization, Project administration. Mansour Shamsipour: Formal analysis, Writing - review & editing. Mohammad Sadegh Hassanvand: Conceptualization, Methodology, Writing - review & editing. Kazem Naddafi: Methodology. Elahe Shahhosseini: Investigation.
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.
Acknowledgments
The authors acknowledge the Institute for Environmental Research (IER) of the Tehran University of Medical Sciences for financially supporting this research (grant number 94-01-46-28285). The authors also thank the Air Quality Control Company for air pollutants data and appreciate the day-care centers for their cooperation.
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