People who live downwind of industrial pig farms experience increased blood pressure.

PROBLEM: Just how bad do industrial pig farms smell? According to personal injury lawyers:

It may start out as a faint stench, but can grow to an odor so overpowering that you can no longer spend time outside for work or pleasure. Some families plagued by nearby hog farms have reported fumes so strong that merely trying to walk outside and get in their cars causes them to double-over retching uncontrollably.

In the U.S., the pig farming industry is concentrated in North Carolina. The state has a concurrent public health crisis: the toxins released by the facilities have known consequences for human health and the environment. In the interest of fully examining the farms' impact, researchers at UNC Chapel Hill's School of Public Health hypothesized that the stench emanating from hog farms could itself be harming neighboring residents.

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METHODOLOGY: 100 people residing within smelling-distance of industrial swine operations volunteered to sit outdoors twice a day for ten minutes. Afterwards, they rated the stench's intensity while researchers measured their blood pressure and asked them, "How do you feel now? Stressed or annoyed?"

Meanwhile, other members of the research team measured the levels of hydrogen sulfide and particulate matter in the air at the center of each neighborhood.

RESULTS: The highest-ranking odors, when compared to stink-free air, were associated with a rise in diastolic blood pressure of nearly 2mmHg. When the concentration of hydrogen sulfide reached 10 parts per billion, systolic blood pressure increased by up to 3mmHg. Particulate matter had no observable effect.

CONCLUSION: As environmental stressors, the authors conclude, the "transient plumes of odorant air pollution" emanating from hog farms "may be associated with acute blood pressure increased that could contribute to development of chronic hypertension."

IMPLICATION: North Carolina's issues with hog farms carry major overtones of environmental injustice: they're concentrated in low income, mostly African American communities where, explain the authors, "older housing and lack of central air condition could increase human exposure to air pollutants." As these populations are already at risk for hypertension, the effects observed here are all the more concerning.

The full study, "Air Pollution from Industrial Swine Operations and Blood Pressure of Neighboring Residents ," is published in the journal Environmental Health Perspectives.