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Dr. Clif Cleaveland

The World Health Organization estimates that 70 percent of premature deaths worldwide — the deaths of 3 million people annually — result from outdoor air pollution. Millions more suffer from asthma and other respiratory diseases, heart disease and stroke that are attributed to air pollution. Recent data also link air pollution to an increased risk of Alzheimer's disease.

Pollution of the air by particulate matter (PM) represents a mixture of solids and liquid droplets. Some particles are released directly from a primary source such as a smokestack. Other particles are formed by chemical reactions that occur in the atmosphere.

Particles are classified by their size. PM whose diameters are in the range of 10 microns (a micron is one- millionth of a meter; the diameter of a human hair is approximately 50 microns) include pollen, dust and mold. Particles in this size range also result also from the burning of wood and some manufacturing processes.

Very small PM, diameters of 2.5 microns and less, are products of combustion: automobiles, factories, fossil-fuel power plants, residential wood-burning and forest fires. PM of this size penetrate deep into lung tissue, resulting in inflammation and permanent damage such as chronic bronchitis and emphysema.

Equipment for monitoring air quality is based upon filtering techniques. Highly sensitive monitors used at the Chattanooga-Hamilton County Air Pollution Control Bureau trap and measure PM as small as 2 microns. Newer technology will permit detection of much smaller PM. The air-quality index is based upon these measurements.

Recent studies analyze the health risks posed by nanoparticles, which are so small that they can enter our bloodstream and central nervous system. Nanoparticles are less than 100 nanometers (nm) in diameter. A nm is one-billionth of a meter. Nanoparticles are produced in abundance by combustion of fuel in internal combustion and jet engines and are present in high concentrations in urban environments. Nanoparticles can only be detected and measured by highly sensitive instruments.

Nanoparticles of magnetite, an iron oxide, are among those found in urban air. Last year, scientists reported their discovery of large amounts of magnetite nanoparticles in 37 autopsied human brains. Millions of particles were detected in a single gram of freeze-dried brain tissue. These particles are known toxins to brain cells. They may also be affected by magnetic fields. Scientists suspect that the particles enter the brain directly by way of the olfactory nerve, the organ for smell, which is situated close to our nasal passages. The particles are linked to Alzheimer disease.

More recent research documents the passage of inhaled nanoparticles of gold from lungs to bloodstream in mouse and human experiments. Fourteen volunteers inhaled air containing gold particles. Within 24 hours, particles appeared in blood and thereafter concentrated in fatty plaques within arteries. This could explain the link between air pollution and heart disease and stroke.

Like so much research, these findings pose more questions. What other types of nanoparticles enter our bodies through polluted air? Does injury to brain cells begin at once or after years of accumulation of nanoparticles? Do nanoparticles in the fatty plaques of arteries speed up the process of atherosclerosis? Do nanoparticles play a role in malignancies in the brain and other organs?

Further research is obviously needed to define the role of environmental nanoparticles in human disease. The Environmental Protection Agency plays a pivotal role in funding, performing, and coordinating this research. Continuing the important work of the EPA should be a nonpartisan goal.

Contact Clif Cleaveland at