Leopold Center for Sustainable Agriculture

Study compares air pollutants in swine hoops, conventional facilities

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By NANCY G. NEWKIRK and PETER S. THORNE, Guest contributers

The Leopold Center and the Center for Health Effects of Environmental Contamination jointly funded swine air quality work recently published in the Journal of Occupational and Environmental Hygiene (Thorne et al. 2009). The overall goal was measure and compare airborne contaminant concentrations inside and outside upwind (100 ft) and downwind (500 ft) of hoop barns and conventional confinement buildings. The study also investigated variables influencing contaminant concentrations such as number of pigs, pig housing density, temperature, wind speed, season and humidity.

Investigators compared conventional swine confinement operations with hoop operations. Hoops are open to the environment and use a composted bedding system as opposed to the conventional method of housing pigs in buildings with slatted floors, under which pits collect their manure slurry. In conventional facilities, animals are housed without bedding and pigs eat, rest and defecate in the same area, often exhibiting aggressive behavior that can increase airborne particulate matter. In a hoop barn, animals are housed in an arched, fabric-roofed structure (resembling a half cylinder) open on one or both ends. Hoops typically have a concrete floor at the front end where pigs eat and the remaining area is covered with straw or corn stover bedding where pigs root and rest; defecation usually is confined to a corner of the building.

Air sampling was performed simultaneously at the two sites. The operations were separated by about 15 miles and no other animal feeding operations were present within one mile. Significant differences in contaminants were observed between hoops and confinement buildings and across seasons for endotoxin, odors, airborne microorganisms and hydrogen sulfide. Endotoxin levels were exceedingly high in both types of barns, averaging over 3,000 Endotoxin Units per cubic meter of air sampled (EU/m3) and ranging as high as 57,800 EU/m3. This is well above the “no effect” level of 50 EU/m3 in terms of respiratory health.

Confinements had seven times more hydrogen sulfide and three times more odor concentrations than hoop barns. Averaged over the study, hydrogen sulfide levels were 150 parts per billion (ppb) in the confinements and 20 ppb in the hoops.

Odor levels in the confinements ranged from 150 to 1800 dilutions with a mean of 430 dilutions. This indicates that, on average, the odor could still be reliably detected by panelists after diluting 1 balloon-full of the barn air with over 400 balloons of pure air. Downwind 500 feet from the confinement barns, odor was reduced to 60 dilutions.

Differences by barn type, number of pigs, and, in some cases, temperature and humidity also were observed. The time of year that the sampling was done also affected contaminant levels in both systems. Whereas hoop barns had highest concentrations of endotoxin and odor in the fall, confinements showed the highest levels in the spring. Both types of swine operations produced high airborne concentrations of endotoxin, odor, hydrogen sulfide, bacteria and fungi that exceeded recommended exposure limits. Endotoxin and odors were found downwind at concentrations that have been previously associated with adverse health effects.

The amount of time a person is exposed to contaminants inside confinement buildings has been linked to increased respiratory symptoms. Swine confinement workers have an increased risk for the development of chronic respiratory symptoms such as bronchitis, occupational asthma and respiratory tract infections or disease, and their lung function can decline rapidly over time. Even so, workers represent a highly selected population and actually may be less susceptible to exposures in livestock feeding operations than the general public. People living or attending school in the vicinity of large-scale confinement facilities versus those who do not may be at increased risk of developing respiratory symptoms, diminished quality of life, depression and mood disorders.

Conclusions

This study investigated relatively small animal feeding operations that do not necessarily represent the largest facilities in the pork industry. The majority of swine operations in the United States have fewer than 5,000 hogs. However, 54 percent of U.S. pork production is from 110 larger facilities with more than 50,000 hogs, and 78.5 percent is from operations with more than 5,000 hogs. Thus, it is expected that data from this study underestimates exposures from very large livestock confinement operations, while providing reasonable estimates of the majority of swine operations.

Statistical tests that compared contaminants between hoop barns and conventional confinement buildings demonstrated significantly higher levels of hydrogen sulfide and odor in confinements and significantly higher total microbes and viable bacteria in hoops. Hoops were found to produce substantial toxicant air emissions and cannot be considered less polluting than conventional confinement operations.

This study also identified contaminant concentrations that exceed recommended exposure limits for human health including endotoxin, odor, and bioaerosols. Statistical analysis models for in-barn endotoxin, inhalable dust, odors and total microbes showed differences by barn type while season was an important predictor for endotoxin, odors, viable bacteria, and total microbes. These findings point to contaminants of concern for animal and human health and suggest the factors that govern their production and release.

Nancy Newkirk is coordinator of the Environmental Health Sciences Research Center at the University of Iowa.

Peter Thorne is professor and acting head of the Department of Occupational and Environmental Health at the University of Iowa.

Back to Leopold Letter Winter 2009