Collaboration in Civic Spheres

New report: urban traffic pollutants can lower birth weight

by Melissa Steffan August 16th, 2011

According to a new study from the National Institute of Environmental Health Sciences polluted air from diesel and gasoline combustion and paved road dust increases the likelihood of low birth weight among infants by as much as five percent for every 25 percent increase in carbon monoxide (CO), nitrogen dioxide (NO2) and polycyclic aromatic hydrocarbons (PAHs), and can contribute to other fetal development problems. A research team from University of California Los Angeles, University of California Berkeley, and University of Southern California determined that low birth weight was more prevalent among pregnant mothers exposed to the higher levels of carbon monoxide, nitrogen dioxide, and other traffic pollutants found in urban environments. The study, titled “Traffic-Related Air Toxics and Term Low Birth Weight in Los Angeles County, California,” was also supported by the California Air Resources Board, and published last week in the journal Environmental Health Perspectives.

According to the report, worldwide research shows some connections between low birth weight, or fetal growth restriction, and levels of traffic pollutants such as carbon monoxide (CO), nitrogen dioxide (NO2) and polycyclic aromatic hydrocarbons (PAHs). PAHs are ultrafine particles created by fuel combustion in vehicles and can be inhaled directly. In pregnant women, research shows that PAHs may cause “adverse changes in placental transport,” disturbing fetal development. Additional previous research suggests this may be particularly likely for pregnancies which are already facing higher odds of term low birth weight due to other factors, and that those odds are increased further based on residential proximity to traffic.

Between June 2004 and March 2006, researchers studied 100,938 births to women living within five miles of a government air quality monitoring station in Los Angeles County, and who were exposed to high levels of common traffic-related pollutants, including diesel and gasoline combustion and paved road dust, to assess the odds of low birth weight among children born to them. Researchers estimated the average exposure to air pollutants over the period of each pregnancy using three different methods: a traditional Chemical Mass Balance model that estimated emission rates of various pollutants; a list of known air pollutants provided from government data; and land use regression models, or dispersal projections, that classified exposure estimates based on geographic location. The study identifies three specific traffic emissions sources as concerns for fetal health and development. These pollutants include carbon monoxide (CO), nitrogen dioxide (NO2) and polycyclic aromatic hydrocarbons (PAHs).

Overall, the study found that the odds of low birth weight increased five percent for every 25 percent increase above baseline levels in exposure for the length of an entire pregnancy to CO, NO2, and PAHs. However, low birth weight was less common in infants to non-Hispanic mothers and to mothers with greater education. The study reported that female infants, first-born infants, and infants born to mothers younger than 25 years of age were more likely to have low birth weight. In addition, those infants born to mothers who received no prenatal care or used government programs for prenatal support were more likely to have low birth weight.

Researchers determined that, compared to rest of Los Angeles County, the women in this study were “younger, more likely to be Hispanic, more likely to be born in Mexico, less educated, and much more likely to use Medi-Cal or other government programs versus private insurance for prenatal care.” However, it is unclear what effect, if any, these factors may have had on infant birth weight in relation to air pollutants. The authors recommend additional research on the specific relationship between fetal development and these particular pollutants.


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