Pig farm pollution linked to higher blood pressure.

Dec 12, 2012

Wing S, RA Horton and KM Rose. 2012. Air pollution from industrial swine operations and blood pressure of neighboring residents. Environmental Health Perspectives http://dx.doi.org/10.1289/ehp.1205109.

Jeff Vanuga, NRCS/flickr
Air pollution and strong odors emanating from large-scale swine operations may affect blood pressure of people who live nearby, according to new research. Twice a day for two weeks, people in the study sat outside their North Carolina homes, then measured their own blood pressure and rated the strength of odors. When the odors were the strongest, their blood pressure rose slightly. It also rose with levels of hydrogen sulfide measured in the air near their homes. High blood pressure is a risk factor for stroke and other cardiovascular diseases. Many pig operations in North Carolina are disproportionately located in low-income communities of color, where residents already are at increased risk of these diseases.


During the past several decades, livestock production in the United States has shifted from small family farms to large industrial operations. The facilities – referred to as concentrated animal feeding operations or CAFOs – house up to tens of thousands of animals.

Animals raised for food under these conditions require a lot of water and often generate huge amounts of manure. The large-scale operations create numerous environmental health and social concerns locally, regionally and globally. Some major problems are air pollution, water pollution, increased exposure to infectious diseases and environmental justice issues (Pew 2008).

People who live near industrial livestock facilities often complain about poor air quality – commonly foul odors, irritated eyes/noses and respiratory impacts. The main sources of the irritants are animal waste and air ventilated from barns. The waste releases chemicals and particles as it decomposes and is moved, stored and applied as a fertilizer. The airborne pollutants include hydrogen sulfide, ammonia, particulate matter, bacterial toxins and volatile organic chemicals (National Academy of Science 2003).

These pollutants can affect health and well being. Odors can induce stress that may contribute to and enhance illnesses. Previous studies report that exposed communities experience elevated symptoms of illness and eye, nose and throat irritation (Schinasi et al. 2011); depressed mood (Schiffman et al. 1995); and a decreased quality of life by limiting outside activities and social gatherings (Tajik et al. 2008).

Feeding operations in North Carolina typically raise pigs or poultry. Some of the highest densities of swine operations occur in eastern North Carolina. The region has a large proportion of African-American residents and a high risk of vascular diseases.

What did they do?

For two week periods during 2003-2005, 101 adults living within 1.5 miles of industrial swine facilities sat outside twice a day – once in the morning and once in the evening – for 10 minutes. While outside, they filled out a diary and rated the strength of the odor and their stress level. They then went inside and  measured their blood pressure using an automated device.

Researchers measured blood pressure, because it is a good indicator of potential heart effects and disease.

While participants collected data, air pollution monitors near their homes measured levels of hydrogen sulfide – the chemical in decomposing manure that smells like a rotten egg – and particulate matter – dust that comes from industrial swine facilities as well as other sources.

Participants were trained to collect their own data to facilitate frequent measurements at their homes, where the air pollution exposures occurred. Each participant served as his or her own control, as the researchers compared each participant's blood pressure during times of high and low air pollution. This approach eliminates the possibility that age, sex, race or other difference among participants can cause differences in the results.

What did they find?

The reports of odors were associated with elevated diastolic blood pressure (DBP). DBP is the bottom number in a blood pressure reading and measures pressure on the arteries between heartbeats.

DBP increased by almost 2 millimeters of mercury (mmHg) during periods of very strong odor compared to no odor.

Hydrogen sulfide was associated with elevated systolic blood pressure (SBP). SBP is the top number in a blood pressure reading and measures the pressure on the arteries when the heart beats.

A 10 part per billion (ppb) increase in hydrogen sulfide resulted in an increase of nearly 3 mmHg for systolic pressure.

Levels of particulate matter were not associated with increases in blood pressure.

Odor effects were largest among men and participants over 53.7 years old. The effects of hydrogen sulfide were greatest among those who struggled to cope with stress and did not take blood pressure medication. Medication is expected to minimize effects since the drugs partially control blood pressure changes. Blood pressure levels were also linked with reported levels of stress at the time of measurement.

What does it mean?

Airborne hydrogen sulfide and strong smells from animal feeding operations can affect blood pressure in those who live nearby. Both physiologic responses to the chemical pollution and the stress of living with chronic and frequent unpleasant odors may contribute to changes seen in blood pressure following low and high pollution incidents.

This is the first study to examine the health effects of air pollution exposures from industrial livestock facilities on blood pressure. Blood pressure readings jumped two points with the strongest smells and three when hydrogen sulfide increased by levels of 10 ppb. Previous studies have linked other environmental exposures to elevated blood pressure.

The small changes in blood pressure observed in this study could have important public health implications. First, high blood pressure is a risk factor for chronic hypertension, stroke, and cardiovascular disease. Second, these exposures occur frequently for a large number of people who live near large-scale swine facilities and for those near sewage treatment plants, landfills and oil refineries that emit similar malodorous air pollutants, including hydrogen sulfide.

Finally, industrial swine facilities are an environmental justice issue in North Carolina, where the operations are concentrated in poor communities of color, which already have substantial impacts from cardiovascular disease.


Hicken, MT, GC Gee, J Morenoff, CM Connell, RC Snow and H Hu. 2012. A novel look at racial health disparities: The interaction between social disadvantage and environmental health. American Journal of Public Health http://dx.doi.org/10.2105/AJPH.2012.300774.

National Academy of Sciences. 2003. Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs. Washington, DC:National Academies Press.

Pew Commission on Industrial Food Animal Production. 2008. Putting Meat on the Table:
Industrial Farm Animal Production in America

Schiffman, SS, EA Sattely Miller, MS Suggs and BG Graham. 1995. The effect of environmental
odors emanating from commercial swine operations on the mood of nearby residents
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Research Bulletin 17:369-375

Schinasi, L, RA Horton, VT Guidry, S Wing, SW Marshall and KB Morland. 2011. Air pollution,
lung function, and physical symptoms in communities near concentrated swine feeding
. Epidemiology 22:208-215.

Tajik, M, N Muhammad, A Lowman, K Thu, S Wing and G Grant. 2008. Impact of odor from industrial hog operations on daily living activities. New Solutions 18:193-205.



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