Associations between Air Pollution and Exhaled Nitric Oxide in Asthmatic Children along the US-Mexico Border Region

STEFANIE EBELT SARNAT (1), Amit Raysoni (2), Wen-Whai Li (2), Fernando Holguin (3), Brent Johnson (1), Silvia Flores (2), Humberto Garcia (2), Jeremy Sarnat (1)

(1) Emory University, Atlanta, (2) University of Texas at El Paso, (3) University of Pittsburgh Medical Center

     Abstract Number: 382
     Last modified: November 9, 2009

Abstract
INTRODUCTION: The impact of urban air pollution on asthmatic children has been a long-standing concern within the environmental health research community. For the Paso del Norte border region, this concern is exacerbated by the tremendous growth in population living near busy roads and increasing vehicular traffic along the border. Numerous studies have been conducted to examine air quality and health in El Paso and Ciudad Juarez, although few have focused specifically on characterizing exposure to specific traffic-related pollutants such as fine particulate matter (PM), nitrogen dioxide and black carbon (BC). In this study, we conducted the first binational analysis examining the impact of air pollution mixtures on asthmatic children in the sister cities of El Paso and Ciudad Juarez along the US-Mexico border region. METHODS: A total of 58 asthmatic children (ages 6-12 yrs) were recruited to participate in a repeated measures panel study from two schools located in El Paso and two schools located in Ciudad Juarez. Data were collected for 16 consecutive weeks from January to May 2008. Each Friday, children gathered at a designated time and room in their school to undergo exhaled nitric oxide (eNO) sampling. eNO is considered a sensitive marker of pulmonary inflammation in response to air pollution. Concurrent indoor and outdoor measurements of 48-hr coarse PM, fine PM, and BC and 96-hr nitrogen dioxide were collected at each school; similar measurements were collected from local ambient monitoring sites. We examined associations between eNO and indoor, outdoor and ambient pollutant concentrations using linear mixed effects models, controlling for a random subject effect, indoor NO levels, ambient temperature and relative humidity, and time using a first order autoregressive heterogeneous covariance structure. RESULTS: 787 eNO samples were collected over the study period, with 6-16 repeated measures per subject. Overall median eNO levels were 20.0 ppb (range: 2.5-135.0 ppb), with a wide variation in subject-specific median eNO levels (range: 6.8-89.3 ppb). We observed positive associations between eNO and each of the pollutants and microenvironments, with findings of 1-3% increases in eNO per interquartile range increases in pollutant concentrations. Indoor concentrations consistently provided higher magnitudes of effects and stronger statistical significance of associations compared to outdoor and ambient concentrations for all PM measures. Among the PM species, the observed effects of fine PM were statistically stronger than for coarse PM and black carbon. These results for PM were robust to changes in the specification of meteorological control in the models. Analyses are planned to examine the robustness of our findings to the inclusion of ozone in our models. DISCUSSION: Results of this study provide indication of the adverse impact of air pollution on the respiratory health of asthmatic children in the El Paso – Ciudad Juarez, with findings of positive associations between traffic-related pollutant indicators and increased pulmonary inflammation. Moreover, the results suggest that school-based pollutant measurements provide the strongest measures of association, which has implications for defining appropriate environmental health indicators in this region.