Air Pollution, Birth Defects, and the Risk in China (and Beyond)

A woman and child walk in the Forbidden City during heavy pollution in Beijing Photograph by Ed Jones/AFP via Getty Images

After one particularly prolonged spell of smoggy Beijing air in late January, the Atlantic Monthly’s James Fallows posted a provocative piece online titled, “China’s Pollution: The Birth Defect Angle.” In it, he quoted troubling anecdotal e-mails from readers suggesting that China’s degraded environment was taking a heavy toll on the living and the unborn alike. Yet the short piece ended with a question, not a scientific conclusion: Do we know if prolonged exposure to polluted air, water, or food causes birth defects?

It turns out that several scientists, both inside and outside China, have been studying that question in recent years—and their answer is yes. That doesn’t mean that every woman giving birth in a polluted environment, or every child born, will experience lasting health problems, but the trend lines across a population are clear. Depending on the level of pollution and the frequency of exposure, observed impacts range from a rise in severe congenital birth defects to a greater frequency of preterm births and low birth weights, correlated with increased risk for infant mortality and for diabetes and cardiovascular disease later in life.

Tong Zhu, now a Princeton Global Scholar, together with research partners at Peking University Health Science Center and the University of Texas at Austin, recently published results of a 10-year investigation of severe birth defects in one of China’s most polluted regions: coal-rich and coal-darkened Shanxi province. Specifically, the team was investigating the alarming frequency of congenital neural tube defects, in which portions of an infant’s brain, skull, or spine are missing or do not connect properly. Most babies born with this condition live only a few weeks.

In the U.S., for every 10,000 live births, there are 7.5 infants with neural tube defects. In Shanxi province, that number is 18 times higher: 140 infants. “We wanted to understand what’s really behind the problem,” says Tong, who previously worked at Peking University in Beijing. “We wanted to find out what chemicals caused this.”

Over a 10-year period, the researchers gathered placentas from 80 stillborn or newborn infants in Shanxi with the disorder. Based on their analysis, they confirmed that those infants had been exposed in utero to significant levels of pesticides, industrial solvents, and especially polycyclic aromatic hydrocarbons (PAHs), which are released into the air when fossil fuels are burned. In Shanxi, abundant coal is used for power plants as well as for home cooking and heating. “We found higher concentrations [of the chemicals] in the placentas of infants with the birth defects” than in other infants, explains Tong, who says there is a “clear association” between the environment the mother is exposed to and birth outcomes. Their findings (pdf) appeared in the Aug. 2, 2011, issue of the Proceedings of the National Academy of Sciences.

Another significant study (pdf), published in the October 2008 issue of Environmental Health Perspectives, had a silver lining. Co-authors at Columbia University in New York, Chongqing University of Medical Sciences, Fudan University in Shanghai, and Shanghai Jiao Tong University studied two sets of women who delivered babies in a district of China’s Chongqing municipality. A heavily polluting coal-fired power plant in the district was closed in the intervening period, allowing the researchers to compare the birth outcomes before and after its shutdown—and they found a notable difference.

“The fetus is extremely sensitive to exposure to toxic chemicals,” says Frederica Perera, one of the study’s authors and the director of the Columbia Center for Children’s Environmental Health. “The organs and brain are rapidly developing, and the metabolic and DNA repair systems are not as efficient as in adults—there is less ability to clear out toxic chemicals.”

The researchers enrolled two cohorts of nonsmoking mothers and newborns in 2002 and 2005. All the women lived within 2 kilometers of the site of Tongliang power plant, which was closed in 2004. Samples of umbilical cord blood were collected at the time of delivery and analyzed to record the presence of PAHs, mercury, and lead. The children were followed until their second birthday, when standardized tests known as Gesell Developmental Schedules were given to assess their behavioral and intellectual development. The children born in 2002, when the power plant was still operating, on average showed developmental delays, especially in motor skills. Those born in 2005 did not exhibit the same setbacks. “It’s actually a good-news story,” says Perera. “The government shut down the power plant, and you could see immediate improvements” in child and maternal health. The takeaway, she emphasizes, is that policy changes can have swift impact.

While China attracts frequent headlines for its smoggy skies, it’s hardly the only country where air pollution is a concern. A study (pdf) published in the March 2013 issue of Environmental Health Perspectives looked at urban air pollution and birth outcomes in nine countries, including the U.S., South Korea, Brazil, Spain, and Italy. The authors examined 3 million total birth records.

The researchers established a correlation between elevated levels of particulate air pollution and elevated numbers of babies delivered at low birth weights in each of the 14 cities in 9 countries studied. They found a correlation between low birth weight and high PM 10 levels (particulate matter less than 10 micrometers in diameter), and separately, a similar correlation with high PM 2.5 levels (particulate matter less than 2.5 micrometers in diameter). For instance, each increase in PM10 of 10 micrograms per cubic meter was associated with a 3 percent increase in babies with low birth weight. “On an individual level, the risk per person is perhaps not so great, but on a population level—when you consider hundreds of thousands of people impacted—it’s very significant and costly for a government and health-care system to manage” the long-term health implications, says lead author Payam Dadvand of the Centre for Research in Environmental Epidemiology in Barcelona, Spain. Their study did not include research sites in China, where air pollution levels are generally higher than in the nine countries studied.

Global satellite-derived map of PM2.5 averaged over 2001-2006. Map Courtesy Aaron van Donkelaar and Randall Martin at Dalhousie University, Halifax, Nova Scotia, Canada

For a useful global comparison, researchers at Canada’s Dalhousie University have used NASA satellite data on air pollution—yes, aerosols can be detected from space—to create a color-coded world map showing average PM2.5 levels for the years 2001-06. Northern China—including the cities Beijing and Tianjin and adjacent provinces Hebei and Shanxi—is not the world’s only air-pollution hot spot, but it’s among the most consistently hazardous.

Some Chinese officials have recently begun to discuss the problem. The director of the family planning agency in Shanxi province, where Princeton’s Tong examined neural tube defects, told China Daily in 2009: “The problem of birth defects is related to environmental pollution, especially in eight main coal zones.” Hu Yali, a professor at Nanjing University, estimated that pollution accounted for 10 percent of birth defects in China. The vice-minister of China’s national family-planning ministry, which is now being folded into the health ministry, told China Daily, “The number of newborns with birth defects is constantly increasing in both urban and rural areas.” Quite often, China’s most polluted regions, including Shanxi, are among its poorest—local parents have scant resources to care for healthy or sick children.