Dec. 13, 2000 -- A daily stroll or jog through the park might be just what the doctor orders some people not to do, especially if they live in big cities. Scientists who study air pollution have been amassing information that shows tiny airborne particles are causing deaths and illnesses, particularly among older people. The most recent study about this kind of air pollution appears in the Dec. 14 issue of the prestigious New England Journal of Medicine.
Although it may be hard to accept that the air many of us breathe is downright dangerous, the fact remains that it is, according to the new study. John Vandenberg, PhD, the director of the National Research Program for Particulate Matter for the Environmental Protection Agency, doesn't mince words on the subject: "You can see with these large-scale studies [that] ... low levels of pollution are affecting the population. This probably translates into thousands of people having an early death every year, or tens of thousands of people," he tells WebMD.
Polluted air can contain nearly invisible "particulate matter" -- droplets or specks caused by vehicle gases, power plants, waste disposal facilities, fires, and industrial plants. Since 1987, the EPA has sought to monitor and limit particles that are smaller than 1/100ths of a millimeter, or 10 microns, called PM10 because of their dimensions. In addition, even smaller particles called PM2.5 have been regulated since 1997.
Previous studies have shown that PM10 particles are causing illnesses that are shortening people's lives; those with lung and heart disorders are most affected by this pollution. Experts tell WebMD that this newest study provides the strongest and clearest evidence to date that air fouled by these particles is also a killer. One expert said more people die from these particles every year than from second-hand smoke or exposure to radon.
The study was conducted by Jonathan Samet, MD, MS, professor and chairman of the Department of Epidemiology at the Johns Hopkins University School of Public Health, and his colleagues there. They analyzed specific, hourly readings on levels of ozone, carbon monoxide, sulfur dioxide, and nitrogen dioxide, as well as levels of PM10, for a 24-hour period in the 20 largest U.S. cities.
Then they matched the pollution data with death rates in those cities during the following 24-hour period, excluding all deaths caused by accidents, suicide and homicides. What the researchers found was that for every increase in PM10 levels, there was a 0.5% increase in the number of deaths. The largest increase was seen in deaths from cardiovascular and respiratory diseases. They also noted a small increase in deaths that they could attribute to a rise in ozone level.
Among the locations studied were six areas in California: Los Angeles, Oakland, Santa Ana-Anaheim, San Bernardino, San Diego, and San Jose, and three in Texas: Dallas-Fort Worth, Houston, and San Antonio. In addition, Atlanta, Chicago, Cleveland, Detroit, Miami, Minneapolis, New York, Philadelphia, Phoenix, Pittsburgh, and Seattle were included. All told the study encompassed more than 50 million people.
"What this provides is a national perspective on air pollution and its health effects," Samet tells WebMD. "Those who are most at risk are ... likely to be frail and have advanced heart and lung disease. The surprise in this data, and I do think I have been relatively conservative in interpreting the data, is that while we have gotten rid of our smoke stacks, we are still seeing health effects. We are taking the science and putting it together in a way that policy makers can pay attention to and it is important for them to pay attention to this."
Samet adds that the problem of particulate pollution is more pressing than global warming. "The contrast with global warming is we will always be deciding what to do based on models and projections and schedules that really exceed our lifespan. Here it is more immediate and we have evidence of effects."
"This is an important study because of the extreme thoroughness of their examination and their exhaustive analysis. It should convince some of the doubters," says Morton Lippmann, PhD, a professor of environmental medicine at New York University School of Medicine and a member of an EPA advisory committee on particulates.
As a cause of death, particulate pollution "is not in the same category as smoking and traffic accidents but it is bigger than radon in terms of [deaths]. It is analogous to, and larger than, environmental smoke," Lippmann says.
EPA officials recognize the threat of particulate pollution. With an annual budget of $62 million, Vandenberg says the National Research Program for Particulate Matter is the agency's "single largest health research project," and that within the EPA, this project receives more funds than do drinking water programs.
Jane Q. Koenig, PhD, a professor of environmental medicine at the University of Washington in Seattle, as well as Samet and other experts interviewed by WebMD say that people who need or want to protect themselves from particulate matter pollution can follow the same guidelines that are commonly issued on days when ozone levels are elevated. These include staying indoors when possible and avoiding strenuous outdoor activities, which bring pollutants deeper into the lungs.
Avoiding areas of congested traffic, shunning wood-burning devices, stopping smoking, and buying a good air-filtering system using a HEPA filter for home use may also help. A diet with fruits and vegetables that are high in antioxidants may thwart the effects of air pollution.
But these efforts, unfortunately, are likely to be of limited benefit. "There's not much you can do," says Lippmann. "You can retreat indoors [from] ozone. But fine particles follow you indoors. They come in through cracks. You are getting 80% of the particles indoors that you are getting outdoors. All you can do is press for greater action on the part of the EPA to get the sources of air pollution under control." He adds that people could cut down their use of electricity and use more mass transportation.
The EPA is not yet advising people to take any precautions to reduce their risk from particulates based on research available today. But that is likely to change. "In the next year or two, we are going to have much more data on monitoring of particles in the air than we have now," Vandenberg tells WebMD. "We are trying to understand who is affected, why and how."
In the near future, individual cities will be able to post information about their particulate matter levels each day, in the same way that ozone levels and "action days" are broadcast today. When levels are too high, people will be advised to take certain precautions, such as limiting time outdoors. Currently the EPA provides ozone information for many cities and particulate information for a few locations on its web site.