Outdoor carbon monoxide: risk to millions.

In the United States alone, an estimated 3 million individuals--most of them over the age of 65--suffer from congestive heart failure, the inability of the heart to pump out all of the blood that returns to it. A new study now indicates that even federally permissible levels of carbon monoxide, a common air pollutant, can aggravate this life-threatening condition enough to send its victims to the hospital.

"It was really striking," says Robert D. Morris of the Medical College of Wisconsin in Milwaukee, who led the study. "In every city we looked at, there was an elevation in heart-failure admissions on days that carbon monoxide went up." Moreover, this effect appeared regardless of the extent to which the patients had also been exposed to other major gaseous pollutants--nitrogen dioxide, sulfur dioxide, or even ozone.

Carbon monoxide reduces the blood's ability to carry oxygen. Previous studies have shown that high exposure to the pollutant for a short period lowers the exertion needed to trigger chest pain (angina) in susceptible individuals--the health impact upon which current federal limits are based. However, Morris' team found that the carbon monoxide concentrations linked to the increases in hospital admissions could be lower than those needed to bring on angina.

Morris and his colleagues obtained daily records of meteorological conditions and outdoor gaseous air pollutants in seven U.S. cities--Chicago, Detroit, Houston, Los Angeles, Milwaukee, New York, and Philadelphia. They compared the information with 4 years of Medicare data on hospital admissions for heart failure in these cities. Only carbon monoxide readings correlated consistently with hospitalizations, they report in the October American Journal of Public Health.

Approximately 11.6 million people live within the 73 U.S. areas that year after year exceed federal carbon monoxide limits (8 parts per million for 9 hours or 35 ppm for 1 hour), notes Dave Ryan, an Environmental Protection Agency spokesman. But the problem isn't limited to those areas, because "there appears [to be] no threshold for this effect," Morris notes. Even on days that fell well below EPA's limits, he says, his team charted a 20 to 40 percent increase in heart failure admissions for every 10 ppm increase in the gas.

Overall, between 2 and 11 percent of hospital admissions for congestive heart failure, depending on the city, could be traced to carbon monoxide. Those roughly 3,300 such incidents each year cost an estimated $33 million.

Nationally, the tally could run many times that, says Joel Schwartz of the Harvard School of Public Health in Boston. While this constitutes a minor proportion of heart disease, it's not a minor environmental risk, he points out in an accompanying editorial. Hazardous waste sites and toxic air pollutants that pose "much lower" risks are regulated, he notes.

"As the population ages," Morris adds, "the subset that is vulnerable [to carbon monoxide] will only increase."

Though outdoor carbon monoxide results almost exclusively from motor vehicles, these sources spew other toxic pollutants as well, including dust-sized particles. Recently, Schwartz and Morris reported data from Detroit indicating that these easily breathed particles may be responsible for some share of the city's hospital admissions for congestive heart failure (SN: 7/1/95, p.5). Again, Morris says, "this carbon monoxide effect tended to be independent of the other pollutants [fine particles]."

Morris concludes that any lessening of carbon monoxide pollution will show health benefits. To Schwartz, the new findings on congestive heart failure also suggest that "it is time to reevaluate the basis for regulating carbon monoxide."