The relationship between air pollution from heavy traffic and allergic sensitization, bronchial hyperresponsiveness, and respiratory symptoms in Dutch schoolchildren - Children's Health

Environmental Health Perspectives, Sept, 2003 by Nicole A.H. Janssen, Bert Brunekreef, Patricia van Vliet, Francee Aarts, Kees Meliefste, Hendrik Harssema, Paul Fischer

Studies have suggested that children living close to busy roads may have impaired respiratory health. This study was designed to test the hypothesis that exposure to exhaust from heavy traffic in particular is related to childhood respiratory health. Children attending 24 schools located within 400 m from busy motorways were investigated. The motorways carried between 5,190 and 22,326 trucks per weekday and between 30,399 and 155,656 cars per day. Locations were chosen so that the correlation between truck and car traffic counts was low. Air pollution measurements were performed at the schools for I year. Respiratory symptoms were collected by parent-completed questionnaire. Sensitization to common allergens was measured by serum immunoglobulin E and skin prick tests. Bronchial hyperresponsiveness (BHR) was measured with a hypertonic saline challenge. Respiratory symptoms were increased near motorways with high track but not high car traffic counts. They were also related to air pollutants that increased near motorways with high truck traffic counts. Lung function and BHR were not related to pollution. Sensitization to pollen increased in relation to truck but not car traffic counts. The relation between symptoms and measures of exposure to (truck) traffic-related air pollution were almost entirely restricted to children with BHR and/or sensitization to common allergens, indicating that these are a sensitive subgroup among all children for these effects. Key words: air pollution, allergy, bronchial hyperresponsiveness, children, diesel, lung function, respiratory symptoms. Environ Health Perspect 111:1512-1518 (2003). doi:10.1289/chp.6243 available via http://dx.doi.ovg/[Online 10 June 2003]

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Exposure to traffic-related air pollution has been implicated in impairment of respiratory health in children in several recent studies, although the literature is not entirely unequivocal (Brauer et al. 2002; Brunekreef et al. 1997; Ciccone et al. 1998; Duhme et al. 1996; Edwards et al. 1994; Gehring et al. 2002; Hirsch et al. 1999; Kramer et al. 2000; Livingstone et al. 1996; Oosterlee et al. 1996; Pershagen et al. 1995; van Vliet et al. 1997; Weiland et al. 1994; Wjst et al. 1993). Some of these studies were questionnaire based, relating self-reported exposures to self-reported health outcomes (Ciccone et al. 1998; Duhme et al. 1996; Weiland et al. 1994). Others have used objective measures of exposure such as distance to busy roads, traffic counts, and modeled or measured air pollution concentrations (Brunekreef et al. 1997; Oosterlee et al. 1996; Pershagen et al. 1995; Roorda-Knape et al. 1998; van Vliet et al. 1997; Wjst et al. 1993), and objective measures of respiratory function such as spirometry (Brunekreef et al. 1997; Wjst et al. 1993) and allergic sensitization by skin prick test (SPT) or serum immunoglobulin E (IgE) determination (Kramer et al. 2000). Some studies have also employed health care use data to assess the health impact of exposure to traffic-related air pollution (Edwards et al. 1994; Livingstone et al. 1996; Pershagen et al. 1995). Collectively, these studies suggest that living in situations with high exposure to traffic-related air pollution increases the prevalence of chronic respiratory symptoms; however, a relationship with lung function or allergic sensitization has been studied insufficiently to draw firm conclusions. Most studies have not been able to single out specific components of traffic-related air pollution, although some of the questionnaire studies have focused on self-reported exposure to truck traffic (Ciccone et al. 1998; Duhme et al. 1996; Weiland et al. 1994). One study conducted by us used automated traffic counts, which enables us to separate heavy from light traffic (Brunekreef et al. 1997; van Vliet et al. 1997). This study dearly suggested that the lung function was decreased, and chronic respiratory symptoms increased, in association with heavy traffic rather than light traffic. In this article, we describe a large study conducted among children attending 24 different schools that were all located close to motorways with varying densities and compositions of traffic.

Methods

Study design. We studied respiratory health of children from 24 schools situated within 400 m of a motorway, using the International Study of Asthma and Allergies in Childhood, phase II (ISAAC II) protocols for measurements of serum IgE, skin test reactivity, bronchial hyperresponsiveness (BHR), and questions on asthmatic and allergic symptoms. We assessed exposure to traffic-related air pollution using specific traffic-related characteristics (traffic counts for cars and trucks separately and distance of the homes and schools to the highway) as well as estimated annual average concentrations of particulate matter with an aerodynamic diameter [less than or equal to] 2.5 [micro]m (P[M.sub.2.5]), soot, and nitrogen dioxide (N[O.sub.2]) outside all 24 schools (Janssen et al. 2001).

Study locations. First, we identified all city districts in the central southwestern part of the Netherlands that had a school and a large number of homes located within 400 m of a highway. Of the 36 city districts that were identified, 20 were selected. We selected sites to achieve a maximum variation in traffic densities (covering the full range of identified traffic densities) and a minimal correlation between car and truck traffic. If city districts were situated along motorways with similar traffic densities, one city district was chosen on the basis of the distance of the homes and school(s) to the motorway, the size of the city districts, and the number of children attending the school(s). In each city district, we collaborated with the municipal health service to approach one school. If a given school did not agree to participate, another school in the same city district or a school in a city district along a motorway with similar traffic densities was approached. In total, we approached 30 schools to obtain 20 participating schools. Reasons for nonparticipation were mostly nonspecific (reorganizations, recently been involved in other studies, etc.). In addition, four schools (of four approached) that were also involved in a study on respiratory health of children living near Schiphol airport participated, producing a total of 24 participating schools. The 24 schools were situated along 22 different motorway stretches. Three of the schools near Schiphol airport were situated along the same motorway stretch (two on the northeast side and one on the southwest side of the road).