Study links soot levels below EPA standards to higher death rate 

Source: Amanda Peterka, E&E reporter • Posted: Friday, June 5, 2015

A Harvard University study published yesterday links airborne soot to higher death rates in people over age 65, even at pollution concentrations below federal standards.

Researchers said their study was the first to examine how fine particulate matter (PM2.5) affects a broad population, including people in rural areas. Fine particles are about one-thirtieth the width of human hair.

Their results, they said, point to a need for further reducing fine particulate pollution. The study, they added, also shows that improving air quality beyond U.S. EPA standards that were last revised in 2012 could benefit public health.

“Most of the country is either meeting the EPA standards now, or is expected to meet them in a few years as new power plant controls kick in,” Harvard epidemiology professor and senior author Joel Schwartz said in a statement. “This study shows that it is not enough. We need to go after coal plants that still aren’t using scrubbers to clean their emissions, as well as other sources of particles like traffic and wood smoke.”

The Harvard T.H. Chan School of Public Health study was published by Environmental Health Perspectivesand was funded by the National Institute of Environmental Health Sciences and EPA.

There have been a few prior studies that have examined the health effects of exposures below EPA’s daily limit for fine particulates.

Previously, short-term exposure studies have been mostly limited to urban areas for lack of robust data on populations and air pollution levels, researchers said. But it’s difficult to generalize results to rural areas and even across cities because of exposure error issues.

Only recently have researchers begun studying groups of people who are representative of the broader U.S. population.

In its study, the Harvard team studied data from about 2.4 million Medicare recipients living in New England. Mortality records for different ZIP codes were obtained through the Medicare program for the years 2003 through 2008.

The researchers obtained air quality data from fine particulate matter ground monitors and satellite measurements. They matched the ZIP code mortality data with levels of fine particulate matter exposure.

The researchers conducted analyses of death rates at yearly exposures below 12 micrograms per cubic meter — the current yearly EPA standard — and short-term exposures below 35 micrograms per cubic meter — the federal daily limit. They also analyzed mortality rates for annual exposures below 10 micrograms per cubic meter and short-term exposures below 30 micrograms per cubic meter.

“To the best of our knowledge,” the researchers wrote, “this study is the first of its kind restricting the exposure and exploring the dose-response relationship between PM2.5 and mortality below the current EPA standards.”

Their conclusion: Every 10 micrograms per cubic meter in annual exposure was significantly associated with a 7.52 percent increase in mortality. The same increase in short-term exposure was linked to a 2.14 percent increase in mortality.

Both short- and long-term exposure led to higher death rates, even in the analyses that were restricted to pollution limits below EPA’s standards.

“Particulate air pollution is like lead pollution: There is no evidence of a safe threshold even at levels far below current standards, including in the rural areas we investigated,” Schwartz said. “We need to focus on strategies that lower exposure everywhere and all the time, and not just in locations or on days with high particulate levels.”

Limitations in the study include limited data about behavior, such as smoking, that could affect the results. The authors also did not examine other pollutants, including ground-level ozone, because of a lack of data.