Air pollution from farms leads to 17,900 US deaths per year, study finds

The smell of hog feces was overwhelming, Elsie Herring said. The breezes that wafted from the hog farm next to her mother’s Duplin County, N.C., home carried hazardous gases: methane, ammonia, hydrogen sulfide.

“The odor is so offensive that we start gagging, we start coughing,” she told a congressional committee in November 2019. Herring said she and other residents developed headaches, breathing problems and heart conditions from the fumes.

Now, a first-of-its-kind study shows that air pollution from Duplin County farms is linked to about 98 premature deaths per year, 89 of which are linked to emissions directly caused by hogs. Those losses are among more than 17,000 annual deaths attributable to pollution from farms across the United States, according to research published today in the Proceedings of the National Academy of Sciences.

Animal agriculture is the deadliest emitter, researchers say, responsible for 80% of deaths from pollution related to food production. Gases associated with manure and animal feed produce small, lung-irritating particles capable of drifting hundreds of miles. These emissions now account for more annual deaths than pollution from coal power plants. Yet, while pollution from power plants, factories and vehicles is restricted under the Clean Air Act, there is less regulation of air quality around farms.

“The food system has really flown under the radar” as a source of deadly pollution, said University of Minnesota professor Jason Hill, the lead author of the new report. “But what we eat affects not just our own health but the health of others. We’re showing that directly.”

Jim Monroe, a spokesman for the National Pork Producers Council, criticized the study as “highly suspect,” saying it “irresponsibly draws conclusions based on modeling and estimates.”

“U.S. pork producers have a strong track record of environmental stewardship,” he wrote in an email, citing a 2019 study from Harper Consulting and Southern Utah University that found significant reductions in ammonia content from pig farms.

A spokesman for Smithfield Foods, which operates industrial hog operations in Duplin County, referred The Washington Post to a 2019 report in which the North Carolina Department of Environmental Quality said it did not find significant air-quality problems in the region.

Representatives from the National Cattleman’s Beef Association did not respond to an interview request.

This is the first major report to link air pollution deaths to specific food items, Hill said. While greenhouse gases cause the same amount of warming no matter where on the planet they’re produced, the health effects of air pollution are dependent on atmospheric chemistry, local weather and the size and health of communities living nearby. Only with advanced new air-quality models has it become possible to pinpoint the consequences of pollution produced hundreds of miles away.

“Agriculture is a tough industry” to monitor, said environmental scientist Maya Almaraz, who was not involved in the study. “They’re already working at such thin margins, and really important to the economy. Regulations are not taken lightly in those systems.”

But, she added, “we have to be working with those systems to protect the people who live in those communities.”

Farm pollution is most dangerous when it occurs upwind of densely populated areas, Hill said. Most of the deaths in his analysis happened in California’s Central Valley, eastern North Carolina and the corn belt of the Upper Midwest.

The most insidious kinds of air pollution are known as Particulate Matter (PM) 2.5 - tiny particles one-thirtieth the width of a human hair, which can become lodged in lungs or absorbed into the bloodstream. Exposure to PM 2.5 can lead to asthma and other breathing problems, and over the long term increases risk of dying from heart disease, cancer and stroke.

These particles are directly produced when farmers till fields or burn crops before harvest. They can also come in the form of dust kicked up by livestock in large animal-feeding operations.

This “primary” PM 2.5 is associated with about 4,800 premature deaths per year, the study found.

But “secondary” particulate matter, which is generated when emissions from farms interact with other gases in the atmosphere, is even more problematic. This is especially true for ammonia, a highly reactive molecule released by manure and fertilizer, which can combine with other pollutants such as nitrogen and sulfur compounds to create small, hazardous particles.

“Of all pollutants, ammonia is the one that has the greatest impact on mortality,” Hill said. His analysis suggests that ammonia emissions contribute to about 12,400 deaths per year.

This is what makes pollution from animal agriculture so dangerous, Hill added. At many beef, pork and dairy facilities, animal waste is stored in massive “lagoons,” such as the one near Herring’s mother’s home in Duplin County. There, the microbes that break down feces release huge amounts of ammonia. Many facilities spray nitrogen-rich liquid waste on nearby farm fields, another source of contamination.

Ammonia is also produced from overapplication of fertilizer on crops such as corn. Since much of the nation’s corn goes to animal feed, Hill counted those emissions toward animal agriculture’s footprint.

All those emissions added up to make meat the biggest source of deadly emissions, Hill said. Per serving, the rate of air pollution deaths linked to red meat was twice as high as that of eggs, three times higher than for dairy and at least 15 times higher than all fruits and vegetables.

“This type of research is extremely important,” said Blakely Hildebrand, an attorney at the Southern Environmental Law Center who has fought emissions from North Carolina hog farms. “The lagoon system that has existed for decades harms people and harms the environment and it’s time for a change.”

Because ammonia is so reactive, it’s difficult to detect unless huge amounts are released at once. When the North Carolina Department of Environmental Quality agreed to monitor air pollution in Duplin County as part of a settlement with REACH and other civil rights groups, it found five instances of elevated ammonia levels, none of which were high enough to trigger federal action. The program was discontinued after a year, when the department said it found no significant air quality problems.

The survey was criticized as inadequate because the department intentionally sited its monitoring stations far from hog farms. Almost all Duplin County residents live within three miles of at least one of these operations.

And the health disparities in Duplin County and places like it are substantial. A 2018 study by researchers at Duke University found that mortality rates in North Carolina communities with hog farms were 30% higher than in the rest of the state. California’s San Joaquin Valley, another hot spot for ammonia pollution, has the highest rate of childhood asthma in the United States, according to the American Lung Association.

“You go through the Central Valley and it’s just this thick layer of gray,” said Almaraz, who is the program manager for the Working Lands Innovation Center at the University of California at Davis.

Although California has some of the country’s strictest air-quality standards for cars and smokestacks, she said, “we’re not really doing anything at a regulatory standpoint to decrease emissions coming from farms.”

“But recognizing these sources really provides mitigation opportunities,” she added. “Now that we know this is an important source, what can we do about it?”

Hill and his colleagues found that farmers could halve the number of air pollution deaths from food production by changing their practices. Instead of leaving manure to decompose in lagoons, they could incorporate it into soil as fertilizer. Covering lagoons, separating urine from feces and controlling the acidity and temperature of lagoons would also reduce ammonia emissions.

“We know the technology is there,” said Devon Hall, an environmental justice advocate who co-founded the Rural Empowerment Association for Community Help in Duplin County. “And we would hope that the industry would do the right thing.”

Targeted fertilizer applications would reduce the amount of ammonia released into the air on croplands, Hill said. Reducing tillage and burning of waste and cutting emissions from equipment could also lead to small health gains.

But the greatest power to save lives lies with consumers, the scientists found. If Americans switched to a “flexitarian” diet, getting at least half their calories from fruits and vegetable and limiting animal protein to a few meals per week, air pollution mortality from agriculture would fall 68%.

That cultural shift would deliver a host of other benefits. Research suggests that reducing meat consumption could reduce global mortality by 6% to 10%, preventing hundreds of thousands of premature deaths.

Meat production is also the most resource-intensive form of agriculture. Thirty percent of Earth’s ice-free land mass is used for pasture for livestock, and red meat requires more water and carbon than any other food. If Earth’s biggest beef eaters limited their intake to 1 1/2 hamburgers a week, they could avoid about 5.5 billion tons of greenhouse gas emissions per year - twice the annual emissions of India.

Discussions about dietary changes are always sensitive, Hill acknowledged. When Colorado Gov. Jared Polis, a Democrat, declared a “MeatOut” day in March, Republican state senator Barbara Kirkmeyer called it an attack against her county, and the Colorado Cattleman’s Association called for people to flock to restaurants and order meat dishes.

But Hill hoped the study would give consumers one more thing to consider when they’re putting food on their plates.

“It’s one thing to eat a low-carbon diet,” he said. “But it’s another to say, ‘Gosh if I eat this delicious lentil dish instead of a hamburger it might be better for my own health but also for other people.’ "