A growing body of research from around the world indicates that smog is exacting a much greater toll than previously known on infants and unborn babies.
Scientists have long known that the extreme levels of air pollution found in the developing world can harm babies, and that lesser pollution in U.S. cities can sicken or kill the elderly and infirm.
The new research shows that the harmful effects of dirty air can extend even into the womb.
More than a dozen studies in the United States, Brazil, Europe, Mexico, South Korea and Taiwan have linked smog to low birth weight, premature births, stillbirths and infant deaths.
In this country, the research has documented ill effects on infants even in cities with modern pollution controls, including Los Angeles.
The findings have helped prompt California officials to seek more stringent smog controls.
"Smog can harm the health of babies," said Beate Ritz, an epidemiologist at UCLA's Center for Occupational and Environmental Health. "This should make us pause. Air pollution doesn't just impact asthmatics and old people at the end of life, but it can affect people at the beginning of their life, and that can disadvantage people throughout their life."
A UCLA study conducted by Ritz and scheduled for release Dec. 28, for the first time links air pollution and birth defects in Southern California.
Other experts say that although worldwide research shows a strong correlation between air quality and infant illnesses, it does not establish a conclusive cause-and-effect connection.
Most of the studies have been analyzed by disinterested scientists--a process called peer review--and have been published in leading journals or will be soon. The studies differ on which pollutants are of most concern.
Some implicate gases, others blame particles, and some point to both.
"The research is suggestive, but preliminary. It's something to be concerned about, but nothing to panic about," said Tracey Woodruff, a senior scientist for the U.S. Environmental Protection Agency and an author of one of the research papers.
"It's something we need to pay attention to."
Some Skeptical, Others Troubled
Frederick W. Lipfert, a New York environmental consultant hired by auto makers, the steel industry, the U.S. Department of Energy and the Electric Power Research Institute to critique several of the reports, downplayed the findings.
"These studies raise more suspicions than smoking guns," he said.
Nonetheless, the research, especially the studies focusing on U.S. cities where pollution levels have been declining, is regarded by health experts as troubling.
"We know there are serious health effects from low levels of air pollution," said Aaron Cohen, an epidemiologist and principal scientist for the Health Effects Institute in Boston, a joint enterprise of the EPA and several pollution-generating industries, including oil companies and utilities.
"When something affects babies and children, everybody takes it seriously. I think it's a high priority that we follow up on these studies," Cohen said.
In the latest research from UCLA, Ritz and a team of researchers found that women exposed to high levels of ozone and carbon monoxide were three times more likely than others to have babies with cleft lips and palates and defective heart valves.
The researchers looked at thousands of pregnant women in the Los Angeles area from 1987 to 1993, and compared those living in areas with relatively dirty air to those living in cleaner areas.
Virtually the entire study area, bounded roughly by San Bernardino, Santa Ana and Santa Clarita, met federal standards for carbon monoxide, and much of the region complied with ozone requirements.
The study, to be published in the American Journal of Epidemiology, found that the greatest risk occurs during the second month of pregnancy, when a fetus gains most of its organs and much of its facial structure.
The Clean Air Act regulates smog levels to protect certain sensitive groups, including children, the elderly and people with respiratory ailments, but not babies or fetuses.
Pollutants inhaled by pregnant mothers can reach fetuses through the umbilical cord, research has found.
Most of the studies about smog and babies came after the Clinton administration set new federal limits for ozone and microscopic particles.
EPA officials say that before those standards can be strengthened, more research is needed to determine which pollutants are most harmful and at what stage of pregnancy they do the most damage.
State Officials Push for Action
However, California officials say they have seen enough. Melanie Marty, chief of the air toxicology and epidemiology unit at the state Office of Environmental Health Hazard Assessment, said the studies linking smog and harm to babies are part of a body of evidence the state is relying on to recommend that the Air Resources Board lower the statewide standard for airborne particle pollution by 33%.
"These studies are very suggestive of effects in infants, and in terms of public health, you want to protect against that rather than wait for the most perfect study in the world," Marty said.
Recently, more and more scientists--many of them women--have been investigating whether ill effects of smog persist even where the pollution has been reduced, as in much of the United States.
A study by scientists from the Harvard School of Public Health and the University of Basel in Switzerland concluded that as many as 11% of infant deaths in the United States--about 3,000 per year--may be a result of microscopic particles in the air.
The study, which has yet to be published, expands on earlier research by the EPA and Centers for Disease Control that looked at 4 million infants in 86 metropolitan areas and compared the incidence of mortality with fluctuating rates of particulate pollution.
That study concluded that as particulate matter increased in the air, the infant mortality rate rose by 10% to 40%.
Carbon Monoxide, Underweight Babies
In a separate study, a team of researchers from the United States and Sweden found that pregnant women in five U.S. cities who were exposed to elevated levels of carbon monoxide during their third trimester were 31% more likely to give birth to underweight babies.
They found that when concentrations of carbon monoxide increased by 1 part per million, the risk climbed by nearly one-third.
The researchers, from Johns Hopkins University, the Centers for Disease Control and Prevention and the Nordic School of Public Health in Sweden, examined 90,000 births and air pollution trends between 1994 and 1996 in Boston; Hartford, Conn.; Philadelphia; Pittsburgh; Springfield, Mass.; and Washington, D.C.
The findings were published in June in the journal Environmental Health Perspectives.
Another study by UCLA researchers, which was published last year and focused on Southern California, concluded that mothers are 20% more likely to have a baby prematurely when exposed to elevated amounts of microscopic particles in the final six weeks of pregnancy.
The analysis, which examined 97,518 newborns between 1989 and 1993, found the highest rate of premature births in eight communities where smog levels were among the highest in the nation though generally in compliance with federal standards.
The communities are Anaheim, Burbank, central Los Angeles, El Toro, Glendora, Hawthorne, Long Beach and Santa Clarita.
The researchers adjusted the findings to account for a variety of factors often related to premature birth, including the mother's age, access to prenatal care, smoking and illnesses such as lung disease, diabetes and hypertension. They excluded births by caesarean section.
In a 1998 study of pregnant women in Sao Paulo, Brazil, scientists found that women exposed to high levels of nitrogen and sulfur oxides were 18% more likely to have their pregnancies terminate in stillbirths.
Nitrogen and sulfur oxides, produced by fuel combustion in vehicles and factories, is more abundant in Sao Paulo than in U.S. cities.
The Sao Paulo researchers also found evidence of carbon monoxide in the umbilical cords of 47 nonsmoking mothers.
The levels of carbon monoxide rose and fell with daily air pollution levels. Carbon monoxide can cut off oxygen to a fetus, leading to death.
The discovery of carbon monoxide in umbilical cords helps explain how air pollutants reach a fetus and cause damage.
"There really is evidence that levels of air pollution encountered in large cities worldwide may be hazardous to the fetus," said Dana Loomis, a co-author of the study and an epidemiologist at the University of North Carolina.
"This is something that has not been recognized before. It was always assumed the fetus was isolated in the womb from things in the environment."
The EPA is weighing the emerging body of research as it considers whether to tighten its standard for airborne particles.
"We do see the trend. There is a growing body of literature finding an association of conventional air pollution and infant mortality," said John D. Bachmann, associate director of science policy in the EPA's air division.
"Our review is in mid-process, and we are looking at all of this."