By Greg Barnes
Airborne particulate pollution in the Charlotte area is associated with a significantly increased risk of hospitalization and death from Alzheimer’s disease, a new study by Duke University shows.
The study, published July 9 in the online journal PLOS One, also found an elevated risk of non-Alzheimer’s dementia and Parkinson’s disease in the Southern Piedmont, but at a lower level than for Alzheimer’s disease.
The study found that Alzheimer’s disease in the Charlotte area caused 323 deaths per 100,000 residents. That is significantly higher than the study’s control subjects, who lived in ZIP codes that reported lower airborne particle pollution. In the control group, 257 deaths from Alzheimer’s per 100,000 residents were recorded.
Particle pollution — known as PM 2.5 — in the Southern Piedmont does not exceed the U.S. EPA’s annual average daily air quality standard of 12 micrograms of particulate matter per cubic meter of air. But at 10.27 micrograms per cubic meter of PM 2.5, it does exceed the more stringent annual average daily standard of 10 micrograms per cubic meter set by the World Health Organization. No areas of the state exceed the EPA’s standard.
Traffic largely the cause
Most of the particulate pollution in the Southern Piedmont comes from traffic, though coal-fueled power plants and other industries play a role, said Dr. Julia Kravchenko, an assistant professor in Duke’s Department of Surgery and corresponding author of the study.
On Thursday (July 22) in Charlotte, PM 2.5 measured 84 micrograms per cubic meter of air, several times higher than the WHO’s daily exposure recommendation of 25 micrograms per cubic meter, according to the North Carolina Air Quality Forecast Center. That was also more than the EPA’s recommended standard of 35 micrograms per cubic meter on a given day. The particulate matter was even slightly higher in Raleigh that day, likely because of smoke coming from a massive wildfire in Oregon. In Wilmington, PM 2.5 measured 60 micrograms per cubic meter on Thursday, according to the website.
How large are airborne particulates?
PM stands for particulate matter (also called particle pollution): the term for a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope.
Particle pollution includes:
- PM10 : inhalable particles, with diameters that are generally 10 micrometers and smaller; and
- PM2.5 : fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller.
- How small is 2.5 micrometers? Think about a single hair from your head. The average human hair is about 70 micrometers in diameter – making it 30 times larger than the largest fine particle.
Particulate matter in the Charlotte area is typically the highest in the state, usually slightly above the WHO’s standard but below the EPA’s standard. That was a main reason the Duke researchers chose the Southern Piedmont for its study, Kravchenko said.
Kravchenko and other researchers analyzed North Carolina mortality and hospital admissions data for associations with levels of particle pollution. They identified 87 North Carolina ZIP codes where particulate matter was above the recommended WHO level and compared them with 81 ZIP codes in the state with lower pollution levels.
While the 87 ZIP codes were confined to the Southern Piedmont, Kravchenko said the other ZIP codes were spread throughout the state and were chosen because of their lower levels of PM 2.5. The particulate matter in the air for the Charlotte area measured over 10 micrograms per cubic meter, compared with 7.6 in the control group, she said.
“Even with this not such pronounced difference between two groups, we were able to see certain associations with higher mortality risk and hospital admission risk” for Alzheimer’s disease, Kravchenko said. “It’s a very important finding in our study, because that means that people shouldn’t be exposed to very high levels of this contaminant.”
The researchers adjusted for co-factors such as race, sex, income, education, health care access, smoking prevalence and arsenic, which is naturally occurring in topsoil in the Charlotte area and is believed to be a risk factor for Alzheimer’s disease.
“Even with the adjustments, the risk of death from Alzheimer’s disease was 35% higher in populations living in zip [sic] codes with particulate matter levels exceeding the WHO standard compared to the residents of NC areas with lower levels,” Sarah Avery, a Duke spokeswoman, wrote in a release announcing the study’s findings.
More studies needed
Kravchenko said the researchers studied other areas of the state with particle pollution levels measuring between those found in the Southern Piedmont and the control group and discovered a corresponding increase in the rate of hospitalizations and death from Alzheimer’s disease.
This is not the first study that has found a correlation between air pollution and the increased risk of neurological conditions, including Alzheimer’s and Parkinson’s disease. But Kravchenko said the Duke study differs in that it focused on much lower levels of particulate matter and still found a correlation with Alzheimer’s disease.
“So we think that it could be useful to have these results, and probably it will help in the future to decrease these high levels of mortality from Alzheimer’s disease in this area,” she said.
Kravchenko said she hopes the Duke study leads to additional ones for the Southern Piedmont that will drill deeper into the risk factors for individuals and the properties of the particulate matter itself, including heavy metals, that could be contributing to the higher rates of the disease.
Clarification: This has been edited to reflect the correlation between air quality and Alzheimers, not that one definitively causes the other. We’ve also clarified the text to reflect that both the EPA and the WHO have daily standards for PM pollution and annual daily average standards for the particulate pollution.