Fine particles, a major threat to children

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Abstract

Background

There is a growing body of evidence for serious health consequences of exposure to ambient air pollution. The general question of who is susceptible is one of the most important gaps in current knowledge regarding particulate matter (PM)-related health effects. Who is susceptible depends on the specific health endpoint being evaluated and the level and length of exposure. Here, we restrict the review on the impact of fine particle exposure on children's health to the following outcomes: infant death, lung function, respiratory symptoms and reproductive outcomes.

Methods

This is a strategic review of children's susceptibility to ambient fine particles and characteristics of infant and children which underlie their increased susceptibility to PM.

Results

Ambient fine PM is associated with intra-uterine growth retardation, infant mortality; it is associated with impaired lung function and increased respiratory symptoms, particularly in asthmatics. Concerning infant mortality, exposure to PM is strongly and consistently associated with postneonatal respiratory mortality and less consistently with sudden infant death syndrome. Although most of the studies reported adverse effects for this health outcome, the evidence is weaker than for infant death. Exposure to fine PM has been associated with impaired lung function and lung function growth. Most of the studies reported increased prevalence of symptom with increased exposure to fine PM.

Conclusion

Fine PM is a major threat to children, because of their higher exposure to PM compared to adults, the immature state of the lung in childhood and also of the immune function at birth. The first months of life might be a period of particular sensitivity. Although the mechanisms of air pollution effects have not yet been completely understood, pregnant women, infants and children need specific protection against exposure to fine particles.

Introduction

The effects of ambient air pollution exposure on human health have been extensively studied during the past five decades. There is a growing body of evidence that there are serious health consequences of exposure to ambient air pollution. The most up to date results of research on health effects of ambient air pollution and in particular of particulate matter (PM) are summarized in several reviews (WHO, 2000, WHO, 2005; US-EPA, 2004; Pope and Dockery, 2006). Further summaries focussed on the situation in Europe (WHO, 2003; RIVM, 2002; SRU, 2002) and in Germany (Kappos et al., 2004). Most of these reviews are also accessible via the web (Reviews/links, 2006).

More specific reviews concerning the health effects of air pollutants on reproduction, fetal and child health have also been published (Maisonet et al., 2004; Glinianaia et al., 2004a, Glinianaia et al., 2004b; Sram et al., 2005; Lacasana et al., 2005).

The health consequences are not equal for the entire population. In many of these documents, ambient PM is considered as a major threat to children and children were considered as a vulnerable and susceptible subgroup of the total population that needs special attention. Here, we will summarize health consequences of exposure to fine particles in infants and children and will discuss why fine PM is a major threat to children.

Section snippets

Characteristics of ambient PM

Ambient particulate air pollution is a suspended mixture of solid and liquid particles which form the atmospheric aerosol. Gaseous components which might be solved in the liquid droplets also belong to this aerosol. The atmospheric aerosols vary in particle mass, number concentrations, size, shape, surface area, chemical composition, physical properties, solubility and sources. The size distribution of total suspended particles (TSP) is trimodal and can be subdivided into coarse, fine and

Are fine particles a major threat to children?

The general question of who is most at risk or most susceptible is one of the most important gaps in current knowledge regarding PM-related health effects (Pope and Dockery, 2006). “Who is susceptible” depends on the specific health endpoint being evaluated and the level and length of exposure (Pope, 2000). Numerous further characteristics have been shown to influence susceptibility to ambient air pollution such as genetic differences, social factors, age, gender, race, pre-existing respiratory

Infant mortality and birth outcomes

There is an increasing body of evidence that exposure to fine particles has an impact on several birth outcomes and infant's health. Effects of exposure to PM were found to be higher for infant mortality than for adult mortality in several studies in the US and Europe using different study designs. An ecological study in the Czech Republic found strong statistically significant associations between infant death rates and PM and SO2 concentrations (Bobak and Leon, 1992), which were also shown

Lung function

Exposure to fine PM has been associated with impaired lung function (Raizenne et al., 1996; Dockery et al., 1982; Roemer et al., 1993; Hoek and Brunekreef, 1993, Hoek and Brunekreef, 1995; Koenig et al., 1993; Neas et al., 1995; Peters et al., 1996; Hoek et al., 1998) and lung function development (Gauderman et al., 2004; Avol et al., 2001). In a short-term effect study from the Netherlands, wintertime PM showed a stronger adverse effect on lung function in the subgroup of children with asthma

Respiratory symptoms

Most of the studies of short-term and long-term exposure to fine PM on lung function also collected data on respiratory symptoms such as wheezing, coughing, etc. These self-reported or parental-reported symptoms were correlated with exposure to fine PM. Most of the studies reported increased prevalence of symptoms with increased exposure to fine PM (Bates, 1995, Bates, 1996; Peters et al., 1996, Peters et al., 1997; Brunekreef et al., 1995; Brunekreef and Holgate, 2002; CEPA/FPAC 1998; Vedal,

Physiologic characteristics of infants and children compared to adults

Children, infants and the foetus differ strongly from adults in toxico-kinetic processes. General differences consist of lower body weight, higher relative weight of liver, higher ratio between body surface and body weight, smaller lung calibre, higher particle deposition in the respiratory tract, generally immature lungs, etc. (Polgar and Weng, 1979; Zeltner and Burri, 1987; Schulz et al., 1997). Children breathe 50% more air per kilogramme of body weight than adults (Zeltner et al., 1987;

Summary and conclusion

Fine PM is a major threat to children because of a higher exposure to PM and immature state of the lungs and possibly also of the immune function at birth. Exposure during the first months of life might be particularly critical. There is an increasing body of evidence that ambient fine PM is associated with infant mortality, intra-uterine growth retardation, impaired lung function, increased respiratory symptoms and exacerbation of symptoms, particularly in asthmatics.

Although the mechanisms of

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