Pregnant women living near the Aliso Canyon gas blowout were more likely to have babies with low birth weight

Women in their final trimester of pregnancy who lived within 6.2 miles of the Aliso Canyon Natural Gas Storage Field blowout - the largest uncontrolled release of toxic air pollutants from an underground gas storage facility in U.S. history - had a nearly 50% higher-than-expected chance of having a low-birth-weight baby, according to a new study by UCLA researchers.

The Aliso Canyon disaster began Oct. 23, 2015, and lasted until Feb. 11, 2016. During those 112 days, approximately 109,000 metric tons of methane and other toxic air pollutants, including benzene and heavy metals, were emitted into the atmosphere near the Porter Ranch neighborhood in northwestern Los Angeles County. Residents reported experiencing foul odors, oily mists and a range of health symptoms both during the blowout and after returning home following evacuations from the area.

In their peer-reviewed study, published today in the journal Science Advances, the UCLA researchers reviewed all Los Angeles County birth records from October 2010 to October 2019, a total of more than a million births.

The researchers focused on 666 births among women who lived within the 6.2-mile-radius impact zone downwind of the facility and who were exposed to the blowout for at least one month during the last 12 weeks of their pregnancy. Among those births, they found that 64 babies, 9.6%, were born with low birth weight (less than 5.5 pounds).

This compares with 6.6% of babies born with low birth weight in the years prior to the blowout in the impact zone - a 45.5% higher likelihood during the blowout.

Across the rest of Los Angeles County, outside the impact zone, 6.8% of babies were born with low birth weight during the period of the blowout; the likelihood was a 41.2% higher for babies born inside the zone.

When excluding low-birth-weight babies born prematurely and looking only at low-birth-weight babies born after at least 37 weeks of gestation - called "term low birth weight" - the prevalence was 66% higher than expected for women exposed in their last trimester. Prior to the blowout, 2.7% of babies were born with term low birth weight in the rest of Los Angeles County and 2.6% in the Aliso Canyon impact zone. During the blowout, however, 4.5% of babies in the impact zone were term low birth weight.

"The nature of the blowout - with a known start date and end date,and a definable geographic area - allowed us to assess the potential effects with a high level of precision," said the study's lead author Kimberly Paul, one of the investigators on the UCLA Aliso Canyon Health Disaster Study team. Paul is an assistant professor-in-residence of neurology at the David Geffen School of Medicine at UCLA.

Thousands of environmental samples taken during and after the blowout showed elevated levels of pollutants known to affect birth weight, including heavy metals and volatile organic compounds such as benzene. At the blowout's peak, an estimated 58 metric tons of methane were released per hour. This was on par with the daily emissions of 4.5 million cars, the study reported.

Low birth weight often correlates with poor fetal growth and nutrition, and hundreds of studies have linked it to in utero pollution exposures. Low birth weight is also associated with developmental and behavioral disorders such as autism spectrum disorder and attention-deficit/hyperactivity disorder, and it increases the risk of several leading adult diseases such as hypertension, diabetes and coronary artery disease.

The researchers also observed a relationship between proximity to the gas plume and birth weights even within the semi-circular impact zone, which they divided into three sections for comparisons. In the two sections of the impact zone where the gas plume was most concentrated, 11.1% of women exposed during their final trimester of pregnancy had a low-birth-weight baby. This figure was more than 70% higher than the occurrence of low birth weight in the same region prior to the blowout and more than 70% higher than the rest of L.A. County during the blowout.

"In the years since the blowout, people in the community have wondered about whether - and how - the blowout might have affected their health," Paul said. "Our results provide evidence that the increase in low-birth-weight babies can be attributed to the gas leak."

Following the blowout, the prevalence of low-birth-weight babies in the affected area returned to expected levels, the study showed.

"Increasing evidence points to in utero and early-life environmental exposures as critical determinants of health through a person's life," said Michael Jerrett, principal investigator of the UCLA Aliso Canyon Disaster Health Research Study and a professor of environmental health sciences at the UCLA Fielding School of Public Health. "Some of the children develop normally, but the risk of all these adverse outcomes goes up when they are born with low birth weight."

In November 2022, the Los Angeles County Department of Public Health awarded a UCLA-led research team a five-year contract of approximately $21 million to assess the short- and long-term health effects of the gas blowout. The study about adverse birth outcomes is the first to be published.

"We know the community has waited a long time for answers, and this is a first substantial step to help them understand the health impacts of this disaster," Jerrett said. "We thank the community members for their feedback and patience throughout this process."