Ambient Ammonia Exposures in an Agricultural Community and Pediatric Asthma Morbidity
Christine Loftus1, Michael Yost, Paul Sampson
1From the aDepartment of Epidemiology, University of Washington, Seattle, WA; bDepartment of Environmental and Occupational Health Sciences, School of Public Health, University of Washington, Seattle, WA; cDepartment of Statistics, College of Arts and Sciences, University of Washington, Seattle, WA; dNorthwest Communities Education Center, Radio KDNA, Granger, WA; eYakima Valley Farm Workers Clinic, Yakima, WA; fPacific Northwest Agricultural Safety and Health Center, School of Public Health, University of Washington, Seattle, WA; and gDepartment of Pediatrics, School of Medicine, University of Washington, Seattle, WA.
Background:
Large-scale animal feeding operations compromise regional air quality in the rural US through emission of pollutants, such as ammonia gas. Exposure to airborne pollution from animal feeding operations may cause pediatric asthma exacerbations in surrounding communities.
Objectives:
To describe spatial and temporal patterns in ambient ammonia concentrations in an agricultural region, and to investigate associations between short-term fluctuations in ammonia and subsequent changes in respiratory health in children with asthma.
Methods:
For 13 months in the Yakima Valley of Washington State, 14 monitors sampled ammonia in outdoor air for 24-hour periods every 6 days. School-age children with asthma (n = 51) were followed for two health outcomes: biweekly reports of asthma symptoms and quick relief medication usage, and daily measurements of forced expiratory volume in 1 second. We assessed associations between each outcome and ammonia using generalized estimating equations.
Results:
Twenty-four-hour ammonia concentrations varied from 0.2 to 238.1 μg/m during the study period and displayed a strong correlation with proximity to animal feeding operations. The percentage of forced expiratory volume in 1 second was 3.8% lower (95% confidence interval = 0.2, 7.3) per interquartile increase in 1-day lagged ammonia concentration and 3.0% lower (95% confidence interval = 0.5, 5.8) for 2-day lagged concentration. We observed no associations between self-reported asthma symptoms or medication usage and estimated ammonia exposure.
Conclusions:
Ammonia concentrations were elevated in this community and strongly predicted by proximity to animal feeding operations. Ammonia's association with acute lung function decrements in children with asthma in the surrounding community may be causal or, alternatively, ammonia may be a marker for other pollutants from animal feeding operations associated with respiratory effects.
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