Elsevier

Environment International

Volume 120, November 2018, Pages 516-524
Environment International

Is smaller worse? New insights about associations of PM1 and respiratory health in children and adolescents

https://doi.org/10.1016/j.envint.2018.08.027Get rights and content

Highlights

  • A large population-based study was conducted in China to assess theses associations.

  • PM1 air pollution was associated with asthma and asthma-like symptoms in children.

  • Boys appeared to be more sensitive to PM1 toxicity than girls.

  • PM1 and children with an allergic predisposition compared to counterparts had strong associations.

Abstract

Background and objectives

Little is known about PM1 effects on respiratory health, relative to larger size fractions (PM2.5). To address this literature gap, we assessed associations between PM1 exposure and asthmatic symptoms in Chinese children and adolescents, compared with PM2.5.

Methods

A total of 59,754 children, aged 2–17 years, were recruited from 94 kindergartens, elementary and middle schools in the Seven Northeast Cities (SNEC) study, during 2012–2013. We obtained information on asthma and asthma-related symptoms including wheeze, persistent phlegm, and persistent cough using a standardized questionnaire developed by the American Thoracic Society. PM1 and PM2.5 concentrations were estimated using a spatial statistical model matched to the children's geocoded home addresses. To examine the associations, mixed models with school/kindergarten as random intercept were used, controlling for covariates.

Results

Odds ratios (ORs) of doctor-diagnosed asthma associated with a 10-μg/m3 increase for PM1 and PM2.5 were 1.56 (95% CI: 1.46–1.66) and 1.50 (1.41–1.59), respectively, and similar pattern were observed for other outcomes. Interaction analyses indicated that boys and the individuals with an allergic predisposition may be vulnerable subgroups. For example, among children with allergic predisposition, the ORs for doctor diagnosed asthma per 10 μg/m3 increase in PM1 was 1.71 (95% CI: 1.60–1.83), which was stronger than in their counterparts (1.46; 1.37–1.56) (p for interaction < 0.05).

Conclusions

This study indicated that long-term exposure to PM1 may increase the risk of asthma and asthma-related symptoms, especially among boys and those with allergic predisposition. Furthermore, these positive associations for PM1 were very similar to those for PM2.5.

Introduction

Several recent reviews on associations between ambient air pollution and respiratory health such as asthma and allergic rhinitis showed controversial conclusions (Anderson et al., 2013; Bowatte et al., 2015; Fuertes and Heinrich, 2015; Gowers et al., 2012; Guarnieri and Balmes, 2014; Heinrich et al., 2016; Khreis et al., 2017; Jacquemin et al., 2015). Reviews that included both cross-sectional and longitudinal studies supported a positive association between air pollution and respiratory health (Khreis et al., 2017), while those based exclusively on longitudinal studies did not show these associations (Bowatte et al., 2015; Fuertes and Heinrich, 2015; Heinrich et al., 2016; Jacquemin et al., 2015). One hypothesis attributes these differences, at least partially, to regional differences in air pollution composition and concentrations (Burbank and Peden, 2018; Cheng et al., 2016; Guarnieri and Balmes, 2014; Jiřík et al., 2017; Liu et al., 2017; Rice et al., 2018; Watanabe et al., 2017). Since most existing studies are from European and North American areas with comparatively low exposures, there is a need to study associations between air pollution and respiratory health in high exposure settings, such as in Asia (Doğruel et al., 2017; Gerez et al., 2010; Kou et al., 2018; Pinart et al., 2017). In China, high rates of population growth, coupled with rapid industrial development and urbanization, have led to well-publicized air quality concerns due to the coexistence of intense coal smoke and motor vehicle emissions. Therefore, China presents an ideal opportunity to examine the effects of ambient air pollution on respiratory health.

While the effects of airborne particulate matter (PM) with aerodynamic diameters <2.5 μm (PM2.5) on asthma and allergies have been widely investigated (Bose et al., 2018; Khalili et al., 2018; Keet et al., 2018; Lavigne et al., 2018; Pennington et al., 2018), few studies have characterized respiratory health impacts for the smaller, and potentially more toxic PM size fraction <1 μm aerodynamic diameter (PM1). PM2.5 can penetrate the small airways and alveoli of the lower respiratory tract, leading to potentially more pronounced health effects (Chen et al., 2017; Mei et al., 2018). PM1 particles are even smaller, and are characterized by high surface area to volume ratio, having an even greater potential for deleterious biological interactions with respiratory tissues and risks for adverse health outcomes (Mei et al., 2018; Borm et al., 2006; Seaton et al., 2010). However, PM1 is not routinely measured because it is not subject to air quality standards in most countries and limited data are available to characterize exposure (Chen et al., 2017; Krzyzanowski, 2008).

In a systematic Medline search, we identified only six relevant human studies examining the effect of PM1 exposure on human health (Chen et al., 2017; Hassanvand et al., 2017; Lin et al., 2016; Wang et al., 2018; Chen et al., 2015; Yang et al., 2018a, Yang et al., 2018b), but none of these studies looked at respiratory outcomes. Furthermore, among these six human-related studies, two studies were panel studies (Chen et al., 2015; Hassanvand et al., 2017), and three studies were both based on Chinese disease monitoring data (Chen et al., 2017; Wang et al., 2018). Only our 33 Communities Chinese Health Study (33CCHS) previously provided a large general population investigation to evaluate the associations of PM1 with diabetes and metabolic syndrome (Yang et al., 2018a, Yang et al., 2018b). To begin to address the absence of evidence on ambient PM1 and children's respiratory health, we used data from the Seven Northeastern Cities (SNEC) Study. Our primary aim was to evaluate the effects of PM2.5 and PM1 on asthma, asthma-related symptoms, and allergic rhinitis in children aged 2 to 17 years. As a secondary aim, we explored whether these associations were modified by sex and allergic predisposition.

Section snippets

Study population and participants

The SNEC was a large population based study designed to examine health outcomes in association with ambient PM exposure among children residing in Liaoning Province, a highly industrialized area in northeastern China. To maximize the contrasts of ambient PM concentrations, in April 2012, we selected 27 urban districts in seven cities as study sites, based on mean air pollution levels during 2009–2012. In total, we selected six districts in Shenyang, five districts in Dalian, four districts in

Characteristics of the study population

From the 63,910 participants, we excluded 4156 children and adolescents (6.50%) that had resided in their current residential address for <2 years. In the final sample of 59,754 children and adolescents, the average age was 10.31 years, and 50.64% were boys. As shown in Table 1, the overall prevalence of doctor-diagnosed asthma (9.51% vs. 6.07%), current asthma (3.50% vs. 1.98%), current wheeze (4.61% vs. 3.31%), wheeze (12.79% vs. 10.07%), persistent phlegm (3.43% vs. 2.80%), persistent cough

Discussion

In this large population-based study in northeastern China, we detected associations between higher concentrations of ambient PM1 and PM2.5 and greater odds for clinical asthma diagnosis and self-reported asthma-like symptoms. All the associations were more pronounced in boys than girls and in those with allergic predisposition than in their non-allergy predisposed counterparts.

Acknowledgement

This work was supported by Major Program of National Natural Science Foundation of China (91543208), Science and Technology Program of Guangzhou (201807010032), the National Natural Science Foundation of China (81872582, 81673128, 81703179, 81472936), National Key Research and Development Program of China (2016YFC0207000), Fundamental Research Funds for the Central Universities (16ykzd02, 17ykpy14, 17ykpy16), Science and Technology Planning Project of Guangdong Province (2014A050503027,

Competing financial interests

The authors declare they have no actual or potential competing interests.

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    These authors contributed equally to this work and should both be list as the first author.

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