Small but Deadly
Agencies monitoring air near highways may be missing the most damaging type of pollution. As a result of combustion, vehicles, power plants, and other industrial sources emit a variety of pollutants, including carbon monoxide, nitrogen oxides, and particulate matter, tiny particles of soot covered in toxic organic chemicals.
Particulate pollution is categorized by the U.S. Environmental Protection Agency into size ranges: PM10 particles are smaller than 10 micrometers, PM2.5 particles are smaller than 2.5 micrometers, and “ultrafine” particles are smaller than 0.1 micrometers. For comparison, the diameter of a human hair is about 70 micrometers. Currently, there is no monitoring or regulation of ultrafine particles.
Particulate pollution exposure has been indicated as a cause of heart disease. Now research from UCLA shows that the ultrafine particles caused more rapid growth of artery-clogging plaques in mice than larger sized particles.
According to Andre Nel, chief of nanomedicine at UCLA, “All types of air pollution is not equal in their danger.”
Nel says, “The smaller particles are the particles that are present in the highest number, they penetrate deeper into the lung, they are retained with a higher degree of efficiency than larger-sized particles, [and] they have a huge surface area.” The larger surface area means they can carry more toxic organic molecules along with them into the body. Those organic chemicals enter the bloodstream and cause damage by creating highly reactive oxygen radicals.
“From the damage that follows the exposure to the oxygen radicals, the body sets up a number of injury responses, which includes inflammation,” Nel explains. It is this inflammatory effect which leads to disease of the lung and probably the cardiovascular system.”
Fortunately, there is a lot of research today being done on antioxidants. “The good news from that side,” says Nel, “is that by making use of drugs or foods that boost antioxidant defense, that we may be able to have a more rational way of intervening in the adverse effects of air pollution.”
Winds of Change
The EPA helped fund this research and other studies. According to Dan Costa, National Program Director of Air Pollution Research, all of the data will be reviewed in an Integrated Science Assessment in the Summer of 2009, but it may be five or 10 years before any ultrafine particle regulations go into effect.
Nel describes some of the challenges. “Because of the size of these particles, it is not easy to capture them and to quantify them, and at the moment, the technology is still not there to monitor ultrafine particle levels.”
And at the moment, several counties in Southern California and in other regions of the U.S. are not even meeting their targets for reducing PM10 and PM2.5 particle pollution.
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