Synergistic Effects of Dust and Ammonia on the Occupational Health Effects of Poultry Production Workers

OBJECTIVE: As production methods for livestock and poultry moved towards large industrial-scale confinement facilities, the occupational health community reported risks for respiratory illnesses in workers. Likely, greater risks for respiratory disease will occur with the continuing trend towards full-time confinement workers, who inspire a combination of bioaerosols, particulates, and gases. Although there have been numerous studies on the individual health effects of air contaminants inside confined animal production facilities, there have been no reports on the effects of combined exposures. The objective of this study was to investigate the combined health effects of air contaminants on poultry production workers. SAMPLE POPULATION: Two hundred and fifty-seven poultry production workers participated in this study. The workers represented various areas of the poultry industry, including turkey growing, broiler production, egg laying, and unloading/shakeling in poultry processing. Worker procedures pulmonary function testing was conducted before and after a four-hour work shift. The work environment was assessed for total and respirable dust, ammonia, endotoxin and CO2. The relationship of simultaneous total dust and ammonia exposures was examined by correlation, logistic modeling, and synergy index calculations. RESULTS: Synergy between ammonia levels and airborne dust explained up to 43% and 63% of the decline (respectively for Forced Expiratory Volume (FEV) in one second and Forced Expiratory Flow (FEF25-75) in pulmonary function over the work shift. Furthermore, assessing the synergy index indicated the combined effect of dust and ammonia is from 53 to 156% (greater combined than individually). The proportion of health effect due to synergy is 35%-61%. CONCLUSIONS: Synergy of simultaneous dust and ammonia exposures in a working environment raises the question of redefining exposure limits for organic dust and ammonia when workers are exposed simultaneously to these substances. CLINICAL RELEVANCE: Control of both dust and ammonia in livestock facilities is extremely important. Lack of control of both these contaminants will increase the risk of respiratory dysfunction to all exposed to this environment, including workers and veterinarians.