Infant mortality rates improve as air quality improves, study shows

Tiny particles in the air probably have a greater impact on infant health than has previously been realized, according to new research published by a University economist, who specializes in environmental regulation, and his colleague.

Their study, which is the largest, most comprehensive study ever conducted on the connection between infant mortality and pollution, examines a sharp reduction in manufacturing and, in turn, particulate air pollution during the 1981-82 recession. Their research suggests that approximately 2,500 additional infants survived to at least 1 year of age than would have without the improvement in air quality.

The scholars, Michael Greenstone, Assistant Professor in Economics, and Kenneth Chay, associate professor of economics at the University of California, Berkeley, reported their findings in the paper, “The Impact of Air Pollution on Infant Mortality: Evidence from Geographic Variation in Pollution Shocks Induced by a Recession,” published in the August issue of the Quarterly Journal of Economics.

Examining data from the recession, they found a striking reduction in infant deaths in counties in which the particulates fell drastically when compared to counties that were similar demographically but did not experience a big drop in the particles. The particles, called total suspended particulates, or TSPs, range in size from barely visible dust particles to those much smaller in size. They include both road dust and other suspended toxic and nontoxic materials.

As part of the federal government’s efforts to promote clean air, the Environmental Protection Agency has set strict standards for TSPs in the air and measures them accordingly. Greenstone and Chay used the TSP figures, coupled with other data, as the source of their study.

“We decided to look at infants rather than adults because at this vulnerable stage of life, pollution may have substantial effects on life expectancy. Further, it is possible to construct complete histories of infants’ exposure to pollution,” Greenstone said. “In contrast, pollution exposure may only slightly hasten the death of already sick adults and the elderly. Further, adults and the elderly may move several times during their lifetime so their lifetime exposure to pollution is unknown, which undermines the credibility of any link between measures of current pollution and current health.”

For the study, the scholars looked at death records from 1,050 of the nation’s most populous counties from 1978 through 1984. They then created matches of counties where 1980-1982 changes in income and other factors were similar and compared the 1980-1982 changes in infant mortality in counties where large drops in TSPs were reported by the EPA and counties in which little change in TSPs was reported.

They found that even a small drop in TSPs reduced infant mortality. A drop of 1 microgram (one millionth of a gram) per cubic meter resulted in five more children surviving for every 100,000 births. For example, Chay and Greenstone’s results suggest that in Chicago, where TSPs dropped 16 micrograms per cubic meter between 1980 and 1982, 70 additional infants survived to the age of 1 in 1982. This reduced the number of infant deaths by about 5 percent.

“The counties that had the largest TSP reductions also had the biggest declines in infant mortality within one year of birth in the 1980 to ’82 period,” the researchers wrote. In contrast, up until about 1980, infant mortality was declining at about the same rate in counties with and without large reductions in TSPs during the recession, indicating that the paper’s findings are not due to differences in trends in infant mortality that predate the sharp 1980-1982 reduction in TSPs.

“Taken together, the evidence provides suggestive evidence of a direct link between particulate pollution and infant mortality,” the paper reported.

Medical researchers have been unable to determine what aspects of air pollution adversely impact the health of mothers and their children. Greenstone and Chay’s research may provide some insights on the mechanism. They found that 60 to 70 percent of the reduced mortality is due to reductions in mortality 24 hours after birth and 80 percent to lower mortality at 28 days. They take this as evidence that maternal exposure to particulates while a baby is in utero may affect fetus development. But, they also determine that the peril is unlikely to be due to low birth weight.

In the last 15 years, the EPA has changed its priorities to more heavily restrict the smallest TSPs. Separate data on small particles was unavailable in the early 1980s, so the research does not establish if the size of particles is a factor.

After the 1981-82 recession, the ambient concentration of TSPs rose modestly nationwide, but has not reached the same level it was before that recession. Thus, the 1980Ð82 recession may have permanently reduced the national infant mortality rate. While the economic hardships imposed by recessions are well documented, Greenstone and Chay said their research appears to indicate a silver lining.