Personal Exposure to Nitrogen Dioxide and Health Effects among Preschool Children

A prospective panel study, in which personal exposure was monitored, was conducted among preschool children in Helsinki between October 1990 and June 1991. The aims of the study were: 1) to assess children’s personal weekly exposure to nitrogen dioxide (NO2), 2) to investigate the association of seasonal and weekly NO2 exposure with respiratory health and 3) to compare different exposure assessment methods in regard to their association with respiratory health. The study was carried out in eight day-care centres in Helsinki, selected on the basis of known traffic density and NO2 concentrations obtained from the network monitoring local air quality. Four day-care centres were located in the central area and four were in suburban areas. All children aged three to six years (N=363) in these centres were invited to participate in the study. A baseline questionnaire including questions on the general health status of the children and on the sociodemographic factors and housing conditions of the families was delivered to parents. Altogether 246 (68%) questionnaires were returned, along with a written consent of participation. The children’s weekly exposure to NO2 was assessed with passive diffusion samplers (i.e. Palmes tubes) in three different ways: personally, both inside and outside the day-care centres. A Palmes tube was fixed on the outer garments of each child for one week at a time for a total of 24 weeks. Only tubes, which had been collecting for 168 ± 24 hours were accepted for analyses. During every week of the study, one tube was placed at a height of 1.5-2 m outside the day-care centre, and another one at the same height in the playing/sleeping room of the children. In addition, NO2 values from the fixed-site monitoring network were used in the exposure assessment. The respiratory health of the children was followed with the help of a daily symptom diary filled in by the parents. In a subgroup of children (N=53), also peak expiratory flow (PEF) was measured at home in the mornings and evenings. Most of the personal weekly NO2 values of the children ranged from 10-50 μg/m. The median exposures in the central area (seasonal 27 μg/m, weekly winter 26 μg/m and weekly spring 28 μg/m) were higher than in the suburban areas (18 μg/m, 18 μg/m ja 17 μg/m, respectively). The personally measured NO2 concentrations were generally lower than the concentrations measured simultaneously inside or outside the day-care centres or at fixed-site monitoring stations. The NO2 concentrations outside the day-care centre, fixed-site NO2 concentration, residential area and characteristics of the home (gas stove, smoking inside, type of dwelling) explained 32% of the variation in personal NO2 exposure in winter and 67% in spring. In regard to respiratory health the children had statistically significantly more days with cough (18 vs. 15%) and a stuffy nose (26 vs. 20%) in the central area than in the suburban areas. However, the seasonal average NO2 exposure (range 11 to 45.8 μg/m) did not consistently associate with the symptoms, but the personal weekly average NO2 exposure (4-99 μg/m) associated with cough (RR=1.52, 95% CI 1.00-2.31). When the other exposure assessment methods were used, there was a non-significant positive trend between NO2 concentration and cough in winter. A non-significant negative trend was found between personal NO2 exposure and PEF. In conclusion, the results of this study suggest that the personal NO2 exposures of preschool children in Helsinki are associated with health outcomes, even though the NO2 concentrations in the ambient air are mostly below the current health-based guideline values on air quality. The associations between short-term NO2 peaks and respiratory health, and the possible long-term influence of ambient air NO2 and pollutant mixtures on the developing lungs of children should be elucidated in future studies.