Coarse Particulate Exposures Not Linked to Hospital Admissions
Exposure to coarse particulate matter air pollution such as from agricultural activities, windblown dust, and mechanical grinding is not statistically significantly associated with emergency hospital admissions for respiratory and cardiovascular diseases among Medicare patients, according to a study in the May 14 issue of JAMA. Health risks of fine particulate matter of 2.5 µm or less in aerodynamic diameter (PM2.5) have been studied extensively over the last decade, the authors note, and there is strong evidence of an association for a higher risk of illness and death. But evidence concerning the health risks of the coarse particulate matter of greater than 2.5 µm and 10 µm or less in aerodynamic diameter (PM10-2.5) is limited, and findings have been mixed. According to background information in the article, coarse particles would likely deposit in the upper and larger airways; particles in the PM2.5 size range, which are more likely to result from combustion processes, can reach the smaller airways and air sacs within the lungs.
Roger D. Peng, Ph.D., of the Johns Hopkins Bloomberg School of Public Health, Baltimore, and colleagues estimated the risk of hospital admissions for cardiovascular and respiratory diseases associated with PM10-2.5 exposure. The researchers used a database assembled for 108 U.S. counties (population larger than 200,000 in 2000) with daily cardiovascular and respiratory disease admission rates, temperature and dew-point temperature, and monitoring of PM10-2.5 and PM2.5 concentrations. Admission rates were constructed from the Medicare National Claims History Files, for a study population of approximately 12 million Medicare enrollees living on average 9 miles from pairs of PM10 and PM2.5 monitors.
There were 3.7 million cardiovascular disease and 1.4 million respiratory disease admissions from January 1999 through December 2005. A 10-µg/m3 increase in PM10-2.5 was associated with a 0.36 percent increase in cardiovascular disease admissions on the same day. However, when adjusted for PM2.5, this association was no longer statistically significant (0.25 percent), the study found. A 10-µg/m3 increase in PM10-2.5 was associated with a nonstatistically significant unadjusted 0.33 percent increase in respiratory disease admissions and a nonstatistically significant 0.26 percent increase in respiratory disease admissions when adjusted for PM2.5. The unadjusted associations of PM2.5 with cardiovascular and respiratory disease admissions were 0.71 percent for same-day exposure and 0.44 percent for exposure 2 days before hospital admission. There were no statistically significant differences in the regional average effects of PM10-2.5 for either outcome, nor were there any significant associations of PM10-2.5 or PM2.5 and cause-specific cardiovascular disease and respiratory disease outcomes.
The National Ambient Air Quality Standard (NAAQS) for particulate matter proposed by EPA in 2005 would have replaced the daily PM10 standard with a daily PM10-2.5 standard, but that proposed standard was not retained in the final proposal because of a need for further evidence. "Currently, national evidence concerning the health risks of short-term exposure to PM10-2.5 is limited, although there is long-standing recognition of how size influences patterns of deposition within the respiratory tract," the authors write. "We did not find statistically significant associations between same day PM10-2.5 concentration and emergency hospital admissions for cardiovascular or respiratory diseases when we adjusted for PM2.5. Nevertheless, we recommend that these findings be considered when the NAAQS for particulate matter is next reviewed, and that the monitoring of PM10 continue so that further studies can be performed."