SANTA ANA, CALIF. — Air pollution may cause serious birth defects, disrupting fetal heart development in the second month of pregnancy, a new study by researchers at the University of California, Los Angeles shows.
The study makes a strong statistical link between birth defects in the Los Angeles basin and air pollution levels recorded by monitoring stations throughout the area.
"This is the first study I'm aware of linking ambient air pollution to birth defects in humans," said Jean Ospital, a health effects officer at the South Coast Air Quality Management District who read the study.
Both Ospital and the study's lead author, Dr. Beate Ritz, say follow-up studies will be needed to confirm the findings. The study makes only a statistical association; exactly which pollutants might have caused the heart defects, or how they interfered with heart formation, remain unknown.
But the large number of children included in the study more than 9,300 babies born between 1987 and 1993 in California's Los Angeles, Orange, San Bernardino and Riverside counties helped ensure that the trends the researchers spotted are likely to be real.
The study matched birth defects tracked by the California Birth Defects Monitoring Program with air pollution data gathered by 30 monitoring stations scattered through the four counties. Mothers who lived within 10 miles of a monitoring station were included.
Of the 9,357 births tracked for the study, 935 resulted in children with heart defects.
One particularly strong "signal" emerged from the data, the authors of the study said. When the levels of carbon monoxide or ozone gas were high, heart defects occurring in the second month of pregnancy when the heart forms jumped up as well, said John A. Harris, a co-author of the study and a pediatrician who is also head of the birth defects monitoring program, based in Oakland.
That is known as a dose-response relationship, when a higher dose in this case, of pollution corresponds closely to a specific problem, he said.
"When you see that in science, that is obviously very provocative," he said. "It's much less likely due to another factor, and much less likely due to coincidence."
The statistics show that the risk of such defects was two to three times greater during episodes of increased air pollution, Harris said. The researchers said in their paper, published Jan. 1 in the American Journal of Epidemiology, that statistical analysis gave them a 95 percent confidence level in their results.
The findings could mean that carbon monoxide and ozone are causing the defects, but not necessarily, Harris said. It could also mean that some other, unidentified pollutant, also present at high levels when carbon monoxide and ozone are high, is to blame.
In either case, auto exhaust is by far the most likely source.
The birth defects linked to pollution included abnormal heart valves, holes in the heart or severely deformed hearts. All of these defects interfere with the heart's ability to pump oxygen through the body; some require surgery before the first year of life, and often, repeated surgeries as the child grows.
Without surgery, such conditions often lead to early death.
Air quality has improved since the data for the study was collected; the Orange County results were gathered between 1987 and 1989.
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