Air pollution may be a bigger health threat than previously believed, a 20-year study of residents of Los Angeles indicates. Researchers report that the contribution of particulate matter to chronic health problems may be as much as two to three times greater than current estimates.

Michael Jerrett of the University of Southern California, Los Angeles and his colleagues analyzed two decades of data collected from nearly 23,000 residents of 260 Los Angeles neighborhoods. They found that as the number of fine particles less than 2.5 microns in diameter increased, so, too, did the risk of dying: each jump of 10 micrograms per cubic meter corresponded to a 11 to 17 percent increase in the risk of dying from any cause. "By looking at the effects of pollution within communities, not only did we observe pollution's influence on overall mortality, but we saw specific links between particulate matter and death from ischemic heart disease, such as heart attack, as well as lung cancers," Jerrett says. The team's findings are published in the November issue of the journal Epidemiology.

In the same issue, a second group of researchers from the Keck School of Medicine of the University of Southern California reports that living close to the freeway raises a child's risk of developing asthma. Tracking the respiratory health of 208 children in 10 cities, the scientists determined that those youngsters who lived closer to highways were more likely to develop asthma. Remarks lead study author W. James Gauderman of Keck: "Considering the enormous costs associated with childhood asthma, today's public policy toward regulating pollutants may merit some reevaluation."