Academic journal article Environmental Health Perspectives

Childhood Incident Asthma and Traffic-Related Air Pollution at Home and School

Academic journal article Environmental Health Perspectives

Childhood Incident Asthma and Traffic-Related Air Pollution at Home and School

Article excerpt

BACKGROUND: Traffic-related air pollution has been associated with adverse cardiorespiratory effects, including increased asthma prevalence. However, there has been little study of effects of traffic exposure at school on new-onset asthma.

OBJECTIVES: We evaluated the relationship of new-onset asthma with traffic-related pollution near homes and schools.

METHODS: Parent-reported physician diagnosis of new-onset asthma (n = 120) was identified during 3 years of follow-up of a cohort of 2,497 kindergarten and first-grade children who were asthma- and wheezing-free at study entry into the Southern California Children's Health Study. We assessed traffic-related pollution exposure based on a fine source dispersion model of traffic volume, distance from home and school, and local meteorology. Regional ambient ozone, nitrogen dioxide (N[O.sub.2]), and particulate matter were measured continuously at one central site monitor in each of 13 study communities. Hazard ratios (HRs) for new-onset asthma were scaled to the range of ambient central site pollutants and to the residential interquartile range for each traffic exposure metric.

RESULTS: Asthma risk increased with modeled traffic-related pollution exposure from roadways near homes [HR 1.51; 95% confidence interval (CI), 1.25-1.82] and near schools (HR 1.45; 95% CI, 1.06-1.98). Ambient N[O.sub.2] measured at a central site in each community was also associated with increased risk (HR 2.18; 95% CI, 1.18--4.01). In models with both N[O.sub.2] and modeled traffic exposures, there were independent associations of asthma with traffic-related pollution at school and home, whereas the estimate for N[O.sub.2] was attenuated (HR 1.37; 95% CI, 0.69-2.71).

CONCLUSIONS: Traffic-related pollution exposure at school and homes may both contribute to the development of asthma.

KEY WORDS: air pollution, asthma, child, epidemiology, vehicular traffic. Environ Health Perspect 118:1021-1026(2010). doi:10.1289/ehp.0901232 [Online 6 April 2010]

The role of air pollution in the development of new-onset asthma remains controversial, and the contribution of this environmental risk factor to the pandemic remains unclear (Eder et al. 2006; Sarnat and Holguin 2007). Although increasing evidence indicates that living near heavy traffic is associated with increased rates of asthma, some well-designed studies have found only weak or no associations (Heinrich and Wichmann 2004; Oftedal et al. 2009).

These inconsistencies may reflect incomplete assessment of exposures to traffic in the microenvironments in which children spend most of their time. Exposure at locations other than home, especially at school where children spend a large proportion of waking hours and may engage in physical activity that would increase the ventilation rate and dose of inhaled pollutants, may have strong influences on occurrence of asthma. However, few studies have examined the effect of traffic-related pollution at schools on asthma rates among children. Two cross-sectional Dutch studies that examined this question reported higher rates of respiratory symptoms among children in schools near roadways with heavy traffic, especially truck traffic (Janssen et al. 2003; van Vliet et al. 1997). A northern California study found that schools downwind from busy freeways had higher concentrations of oxides of nitrogen (N[O sub x]) and higher asthma prevalence rates (Kim et al. 2004). However, in a subsequent analysis of these same data, the effect of school exposure was attenuated and no longer significant after adjusting for modeled residential traffic-related exposure (Kim et al. 2008).

Nitrogen dioxide (N[0 sub 2]) is routinely measured at regulatory monitoring stations. However, these measurements reflect both background regional concentrations and local sources near the stations. Some studies have assessed local exposure to traffic-related pollution using measured N[O sub 2] (or N[O sub x]) as surrogate for the complex mixture of traffic-related pollutants that occurs in close proximity to roadways (Brauer et al. …

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