Nanoparticles in air bad news for people

November 16, 2001

OAK RIDGE, Tenn., - Tiny airborne particles too small to see are more plentiful and may pose a greater health hazard than previously thought, says an Oak Ridge National Laboratory researcher studying airborne particles in the Great Smoky Mountains and beyond.

Recent evidence in scientific literature suggests that a relatively small increase in the concentration of particulate matter of 10 micrometers or less - a tenth the diameter of a human hair -- results in a small but consistent increase in death rates and illnesses caused by impacts on the cardiopulmonary system.

Particles smaller than a couple of hundred nanometers generally come from manmade emission sources such as engine combustion. One micrometer is equal to 1,000 nanometers. Photochemical reactions of air pollutants in the atmosphere can also yield small particles that can undergo changes in size, shape and chemical composition.

Mengdawn Cheng of the Environmental Sciences Division is tracking and characterizing the "nanoparticles" in the Smokies and 29 other sites. He is also examining their toxicity in a process called "direct cell deposition," which was developed by his team. The technique differs from other approaches that involve collecting particles in a solution and then instilling the particles to animals.

"We believe that the instillation approach changes particle properties, size, shape and chemical composition, for example, and therefore we think such a practice does not allow us to study the toxicity of the right particles," Cheng said.

Cheng's research also involves exposing cells directly to engine exhaust, which poses a challenge and had never been done. Cheng and colleagues are especially interested in the health effects resulting from exposure to nanoparticles typically produced by internal combustion and turbine engines and other sources.

Cheng and his co-workers exposed primed and normal human lung cells to synthetic particles and chemically complex particles produced by an internal combustion engine. They discovered that the acute toxicological responses of the primed cells - those that simulate human lungs that are injured or predisposed to lung conditions -- were high compared to that of the normal cells. Through measurements, the researchers also discovered that particles containing several chemical species are more toxic to normal cells than particles containing a single species.

"Such a technique may enable a systematic study of complex mixtures such as environmental particles," Cheng said.

Others from ORNL working on this project, which was funded by the Laboratory Directed Research and Development program, are Boyd Malone of the Environmental Sciences Division, John Storey of the Engineering Science and Technology Division and Clay Easterly of the Life Sciences Division.

In another project, Cheng and collaborators at Lawrence Berkeley National Laboratory, Washington University in St. Louis and the Medical School of (Toledo) Ohio tracked and characterized particles of less than 1 micrometer.

With the help of colleagues at ORNL, the Tennessee Valley Authority, The National Park Service, several universities and other Department of Energy laboratories, Cheng developed new aerosol instruments and measurement techniques. The study involved 30 air sampling sites east of St. Louis. One site was in the Smoky Mountains.

The goal was to gather data to better understand the movement and makeup of ozone and fine particles in the eastern portion of the United States.

"Particles of different sizes can tell us lots of stories about their origins, the geographical areas they have gone through and the atmospheric processes and environments they encountered en route before they were captured," Cheng said.

The fine particles consist of tiny solid or liquid droplets - or both - suspended in the air. Air polluting particulate matter ranges in size from a few nanometers to several hundred micrometers, and Cheng noted that the smallest particles have a very different chemical composition than larger particles. Also, new emission control technologies can do a good job of removing large particles but can do very little about the ultrafine particles. And some technologies produce even more ultrafine particles in the process of reducing emissions of particulate matter.

Nanoparticles behave aerodynamically like gas molecules and have a larger surface area, per unit mass, than large particles. As a result, environmental nanoparticles can penetrate deeper inside human lungs and cause more harm than larger particles because of the increased particle surface area, Cheng said.

Particles smaller than a couple of hundred nanometers generally come from manmade emissions involving high temperatures, energetic reactions or both. These particles are extremely dynamic, varying with time, and are difficult to measure. They can travel 2,000 miles or more.
This project was funded by TVA. ORNL is a Department of Energy multiprogram research facility managed by UT-Battelle.


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