The air we breathe: Studying the impact of air pollution in rural environments

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Agricultural settings have been shown to have high concentrations of particulate matter in the air, due to dusty conditions. (view larger image)

Air pollution is a well-known, much-documented problem in the industrialized world. Those who do not live in major cities see media images of thick, dirty air and crowded streets of people wearing masks over their noses and mouths.

Linked to increases in heart disease, respiratory disease, lung cancer and a host of other health complications, air pollution plays a role in 3.7 million premature deaths each year, according to 2012 data from the World Health Organization. Contrary to the popular portrayal, however, the effects of air pollution are not limited to urban environments. Michigan State University (MSU) AgBioResearch toxicologist Jack Harkema is studying the impacts of air pollution on rural populations.

Air pollution is a mixture of elevated concentrations of potentially harmful gaseous chemicals, like ozone and nitrogen dioxide, and very small particles (particulate matter or particulates) that result from emissions from both human sources, like motor vehicles or industrial smoke stacks, and natural sources, like wildfires or volcanoes. If inhaled these pollutants may cause injury to our lungs or other organs like our heart and blood vessels.

Airborne particulates are defined according to their size into three basic categories: coarse, fine and ultrafine. Fine particles range in size from 2.5 to 0.1 microns in diameter, and ultrafine particles are less than a tenth of a micron in diameter. Both are invisible to the naked eye and even the largest size of fine particles are still 30 times less than the diameter of a human hair. The larger coarse particles with diameters greater than 2.5 microns and smaller than 10 microns are common to rural atmospheres. Fine and ultrafine particles are commonly emitted by automobiles, power plants and industries, while coarse particles are more likely to originate from organic compounds commonly found in the earth’s crust.

“In agricultural settings, you see some of the highest airborne concentrations of particulate matter due to dusty conditions generated by common agricultural practices,” said Harkema, university distinguished professor in the MSU College of Veterinary Medicine and the Institute for Integrative Toxicology. “A lot of people think air pollution is just an urban issue, but we now know that it causes real problems in rural settings, too.”

Harkema’s work in this area blossomed in 2011, when an $8 million grant from the U.S. Environmental Protection Agency  (EPA) established the Great Lakes Air Center for Integrated Environmental Research (GLACIER). Combining the multidisciplinary expertise of researchers from MSU, the University of Michigan, Ohio State University and the University of Maryland, GLACIER is one of four EPA Clean Air Research Centers established to study the health impacts of air pollutants. Each center has a distinctive focus within this research area. GLACIER focuses on understanding the health effects of air pollutant mixtures, especially in susceptible populations like those suffering from chronic cardiovascular, respiratory or metabolic conditions.

Though much of their work has focused on urban air pollution — primarily in communities in and around Detroit — recent research has shifted to rural environments.

Air pollution can be simulated to a degree in the laboratory, but collecting data in the field provides a much clearer picture of the conditions that people are likely to face. Boarding semi-trucks converted into high-tech mobile laboratories, Harkema’s team traveled to Dexter, Michigan, an agricultural community west of Ann Arbor, to study the effects of coarse particle exposure on heart rate and blood pressure in healthy individuals.

Harkema’s long-time collaborator Robert Brook, a cardiologist in the School of Medicine at the University of Michigan, was the principal investigator of the study in Dexter. Together, Brook and Harkema coauthored a seminal scientific paper, reporting for the first time that brief exposures to real-world coarse particulate matter in a rural community can cause elevations in heart rate and blood. These effects on the cardiovascular system were similar to those they found in human subjects after short-term exposure to fine particles in an urban industrial community near Detroit. Though these cardiovascular changes did not compromise the health of these healthy subjects, the investigators speculated that such particle-driven health effects could potentially have detrimental consequences in people suffering from chronic heart disease.

“We’re now finding, like other laboratories, that air pollution affects many other organ systems in the body and may exacerbate pre-existing chronic diseases, such as diabetes and obesity,” said Harkema. “Originally, for example, we thought cigarette smoke caused only lung cancer, but we’ve since learned that it also contributes to breast cancer, coronary heart disease and other systemic problems. I think particulate matter could work in a similar way.”

As areas of the developing world continue to scale up their agricultural industries, Harkema said coarse particulate matter will only become a more serious environmental issue. Fortunately, scientists like Harkema are working to find ways to mitigate its adverse health effects. Every five years, the EPA conducts a review of all of the data on air pollution and its health effects, updating its standards accordingly. Brook and Harkema’s recent findings on particulate air pollution will help it set the air quality standard for particulate matter that aims to protect the health of susceptible populations.

“We’re now trying to understand how exposure to small amounts of fine and coarse particles triggers alterations in blood pressure and heart rate,” said Harkema. “This is not just a small regional problem, it’s worldwide. The work we do here has an impact on protecting human health in urban and rural communities around the world through better air quality standards and guidelines based on sound science.”

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