Risk Effects of Near-Roadway Air Pollutants on Bronchitic Symptoms in Asthmatic and Non-Asthmatic Children

Abstract

Background/Aim: Research indicates that exposures to ambient criteria air pollutants affect bronchitic symptoms, especially in asthmatics, but less is known about the importance of exposures to the near-roadway air pollutant mixture. In the current study, we investigated whether exposure to near-roadway air pollutants was associated with increased risk of bronchitic symptoms among asthmatic and non-asthmatic children. Given previous studies’ findings of associations between regional air pollution and bronchitic symptoms, we also tested whether near-roadway effects differed across communities with high and low regional pollution. Methods: Longitudinal data from 3 cohorts of children (N=7224) participating in the southern California Children’s Health Study were analyzed. Presence of bronchitic symptoms in the past 12 months was assessed over an 8 to 9 year period within each cohort. Residential exposure to the near-roadway air pollution mixture from freeways and non-freeways (with NOx as an indicator) was estimated using the CALINE4 line-source dispersion model. Mixed-effects logistic regression models were used to test the association between near-roadway air pollutants and bronchitic symptoms, allowing for potentially different associations by asthma status and regional air pollution levels. Results: Among asthmatic children, a 2 SD (11.2 ppb) increase in exposure to non-freeway NOx was associated with a 35% increase in the odds of reporting bronchitic symptoms (OR: 1.35; 95% CI: 1.13-1.63), while a 2 SD (37.1 ppb) increase in exposure to freeway NOx was associated with a 24% increase in odds (OR: 1.24; 95% CI: 1.04-1.49). Among non-asthmatic children, only non-freeway NOx was statistically significantly associated with bronchitic symptoms (OR: 1.12; 95% CI: 1.01-1.25 per 2 SD increase). Associations between near-roadway pollutants and bronchitic symptoms were generally strongest among asthmatics living in communities with lower regional PM2.5. Conclusions: Near-roadway air pollution was associated with bronchitic symptoms, and the association varied by asthma status and by regional air pollution.