Fetal Deaths Climb With Air Pollution

alarming statistics

The Alliance For A Clean Environment

Printable Version

Fetal Deaths Climb with Air Pollution
Science News, Vol. 153

Over the past decade, a host of studies has shown that a day or two after concentrations of certain key air pollutants rise, so do deaths among people with respiratory and heart disease, especially elderly people. Now, a Brazilian study has uncovered evidence of a similar vulnerability at the opposite end of the age spectrum–in the womb.

Physicians in São Paulo must report all miscarriages that occur during the third trimester of pregnancy. On most days, there are about 8, though the count can run as low as 1 or as high as 18.

Luiz A.A. Pereira of the University of São Paulo and his colleagues compared daily tallies of these fetal deaths in 1991 and 1992 to daily concentrations of major urban air pollutants: nitrogen dioxide (NO₂), sulfur dioxide (SO₂) carbon monoxide (CO), dust size particulates, and ozone. Though the São Paulo area has dirty air, “levels of pollution there are not that different from what you see in many big cities in (North America),” even in the United States, observes Dana Loomis of the University of North Carolina at Chapel Hill, a coauthor of the study.

Overall, the team found no association between miscarriage rates and either ozone or particulates. However, the number of fetal deaths rose 3 days after measurable increases in each of the other pollutants. NO₂ proved most strongly linked to those variations in miscarriage rates, even after accounting for such possible confounding factors as heat and humidity.

It would appear “that about 20 percent of the fetal deaths may be attributed to the NO₂,” Pereira told Science News. He cautions, however, that “since there is a high correlation among these pollutants” –combustion usually spews copious amounts of all three –it’s unwise to expect, at least at this stage, that any one pollutant is solely responsible.

Indeed, the researchers will report in the June Environmental Health Perspectives, “the most robust association” emerged when they considered variations in NO₂, CO, and SO₂, together, not as individual risk factors.

In a second experiment, Pereira’s team measured carboxyhemoglobin in the umbilical-cord blood of 47 healthy babies born to nonsmokers. Carboxyhemoglobin-produced when CO replaces oxygen in hemoglobin, the oxygen-carrying component of blood-proved most abundant in newborns delivered on days when outdoor CO concentrations were highest.

Since carboxyhemoglobin reduces the blood’s ability to carry oxygen, high outdoor CO concentration may impair a fetus’ ability to get oxygen, the researchers say. In fact, Pereira notes, hypoxia, or insufficient oxygen, was the reported cause of most fetal deaths.

These carboxyhemoglobin data suggest that the study’s links between combustion pollutants and fetal death “were not spurious,” says Richard A. Levinson, associate executive director of the American Public Health Association in Washington, D.C.

The new findings also threaten to reshape discussions of pollution’s social costs. In terms of the impacts of pollutants on years of life lost, most analysts “have focused on the elderly,” observes Loomis. “It would be a completely different story if fetal mortality were implicated.” – J. Raloff