Toxic Plumes from Aliso Canyon Gas Blowout Harmed Babies, Study Shows

22 09 2025 | 22:44Liza Gross / INSIDE CLIMATE NEWS

Infants born to pregnant women exposed to the massive Southern California gas leak were more likely to be underweight, a risk factor for serious long-term health conditions.

Scientists studying the health effects of one of the largest blowouts of natural gas in U.S. history just confirmed what residents long suspected: the massive release of fossil gas carried serious health risks.

On October 23, 2015, employees of SoCalGas discovered a leak in a well at the utility’s Aliso Canyon underground gas storage facility, about 25 miles northwest of Los Angeles. Billowing clouds of toxic gases and the climate super-pollutant methane filled the air for nearly four months as SoCalGas workers tried to fix the leak in a pipe hundreds of feet underground.

Pregnant women who lived within 6 miles of the uncontrolled emissions during their final trimester had up to a 50 percent higher chance of having low birth weight babies than normal, researchers at the University of California, Los Angeles reported in a new peer-reviewed study. Mothers who lived closest to the leak were twice as likely to have underweight babies as women who lived farther away.

Low birth weight—when newborns weigh less than 5.5 pounds—increases a child’s risk of dying before their first birthday and their chances of having developmental issues in adolescence and chronic health problems as adults.

The UCLA research is part of the five-year Aliso Canyon Disaster Research Health Study, launched in 2022 to understand the short- and long-term health consequences of exposure to emissions from the underground gas storage facility, built in a depleted oil field.

“These facilities, when they’re located close to large residential populations, have the potential to generate substantial health effects that may be felt for generations,” said Michael Jerrett, co-principal investigator of the project and director of the UCLA Center for Occupational and Environmental Health. 

The blowout forced two schools to close, displaced more than 8,000 families near the disaster site and triggered thousands of complaints to the L.A. County health department about diverse health ills, including headaches, nausea, vomiting, nosebleeds, respiratory symptoms and dizziness among many other ailments.

This study provides information that’s needed to have “a complete and accurate debate” about the possible costs and benefits of continuing to use large amounts of natural gas in the energy system, Jerrett said. “And this is really the first study that I think has shown that this part of the life cycle of natural gas holds its own potential risks for catastrophic release and potentially large population health exposures to air toxics.”

The team focused on low birth weight partly because it’s such a well-studied indicator of the health of mothers and their babies. Low birth weight babies who survive are more likely to have neurodevelopmental problems, such as autism spectrum disorder and attention-deficit and hyperactivity disorders, and face increased risk of developing chronic adult conditions such as hypertension, type 2 diabetes and heart disease.

Next month marks the 10th anniversary of the catastrophic leak. At the height of the disaster, the failed well—which had been designed to extract oil, not to store Aliso Canyon’s high-pressure gas—released an estimated 58 metric tons of methane per hour, rates comparable to methane emissions rates for the entire U.S. oil and gas industry. 

 

Chemical monitoring detected “exceptionally high concentrations” of methane and ethane, major components of natural gas, the study authors noted, along with potentially harmful odorants that are added to the gas to aid in leak detection, as well as a suite of toxic air contaminants found in natural gas, including the carcinogen benzene. 

In an earlier study, Jerrett and his colleagues detected particles, thought to originate from “well kill” efforts, with air monitors, and found the same metals in soil near the storage facility and in indoor dust samples in L.A.’s Porter Ranch, directly downwind of Aliso Canyon. Residents of the neighborhood also reported seeing oily residue on cars, homes and playgrounds.

Seth Shonkoff, executive director of PSE Healthy Energy who was not involved in the research, called the study novel, well designed and well executed. 

The findings were surprising in their magnitude, said Shonkoff, an expert on the health effects of oil and gas systems, but consistent with new information about what chemicals are found in natural gas along with methane.

 

Companies often don’t disclose what’s in gas, so Shonkoff’s team recently collected and analyzed gas samples from oil and gas facilities around the world, from extraction sites to storage facilities like Aliso Canyon and distribution systems that deliver gas to homes and businesses. 

“Ninety-nine percent of gas samples collected and disclosed by industry and in regulatory filings indicate that there are hazardous air pollutants commingled in natural gas,” Shonkoff said. 

Many of these compounds are associated with low birth weight, preterm birth and miscarriage, he said. And particles, like those found in Jerrett’s earlier study, he added, “are also widely recognized as contributors to preterm birth and low birth weight.”

A Natural Experiment

The nature of the Aliso Canyon disaster offered health researchers a special opportunity. Because it involved a defined exposure period for a distinct population within a specific geographic area, the team could conduct the type of natural experiment that typically isn’t possible with environmental exposure research.

Many studies have linked air pollution to low birth weight, including in Los Angeles. The team took advantage of their access to millions of birth records across the state, along with the defined timing of the exposure, to distinguish between the effects of L.A.’s polluted air and those of natural gas.

They compared birth outcomes for pregnant women who lived in the community during the disaster to women who lived there before and after, as well as to women who lived in unaffected L.A. communities and to women in the rest of the state. 

“We compared women who were giving birth around the same time and no matter who we compared to, we saw the spike,” said study co-author Kimberly Paul, an epidemiologist and UCLA assistant professor of neurology. “The difference of what was happening during this spike was the blowout.”

The researchers weren’t surprised to see the effect primarily in women in late stages of pregnancy because that’s when babies undergo rapid growth and development. They didn’t see associations with low birth weight for women exposed during earlier stages of pregnancy, but they did see a 20 percent increase in male babies born to those women. 

That was unexpected, Paul said, because the proportion of male and female babies at birth in a population is “a very, very stable measure.” Seeing a change in sex ratio suggests that the blowout may have distorted that ratio by leading to more miscarriages of female fetuses among the women who were exposed during their early stages of pregnancy.

The study’s findings are in line with “a fairly strong” body of literature finding adverse birth outcomes associated with living near different types of oil and gas infrastructure, said Shonkoff, who helped conduct an exhaustive review of epidemiology studies for California oil and gas regulators when the state considered its drilling buffer zone law. 

“Adverse birth outcomes were a primary and consistent outcome among epidemiologic studies,” he said.

“The Community Deserves Answers”

Aliso Canyon released more than 100,000 metric tons of methane over four months, Shonkoff said. “But there are major releases of natural gas happening all over the United States and all over the world, and we are learning more and more about them every day.” 

This study’s strong and rigorous design shows that methane super-emitters are not only climate problems but very likely contribute to disease, he said. “We need to pay very close attention to developing rules and regulations that put an end to methane super-emitters across the oil and gas supply chain.”

There’s been an ongoing debate about the continued use of natural gas as an energy source and its potential role as a bridge fuel in the transition to renewable energy, Jerrett said. Finding “significant and measurable health effects” on infants born to women exposed during the Aliso Canyon crisis, he said, gives the government, the community and the gas company better information about whether they should be shutting down the facility. 

More than 53,000 Americans live within a city block of underground gas storage facilities, researchers reported in 2019. 

“If there are ongoing leaks from these facilities, or emissions that are like the Aliso Canyon natural gas leak disaster where there’s this catastrophic fugitive release, the chance of having adverse effects on large populations really increases,” Jerrett said.

Many of these facilities are cited near historically marginalized communities where low-income and pregnant women of color have higher rates of low birth weight babies linked to disproportionate exposure to environmental and social stressors. 

“If you’re in one of these communities, and then there’s a methane super-emitter event, that increased risk gets put on top of the risks that are already there,” Shonkoff said. “And you would expect to see even higher rates of these adverse birth outcomes.”

With climate change turning more and more wildfires, floods and other natural hazards into catastrophic events, Jerrett hopes the study will become a model for how to reconstruct exposures after disasters.

“It’s really important to be able to go back and better understand what those impacts are on populations,” he said, “so that as we go forward and we’re thinking about measures that might be used to control climate emissions or in some other way protect nearby populations from those disasters, we have full information about the possible impacts.”

Jerrett’s team is now conducting detailed clinical assessments and analyzing data from emergency room visits, air monitors, health registries and complaints during the leak to see if they detect an uptick in cancer, autism or other conditions potentially linked to oil and gas exposure.

But several analyses will have to wait until the team’s request for samples from the California Biobank Program gets fulfilled. The samples will allow them to do nontargeted molecular analyses to detect subtle disease markers at the cellular level. The biobank placed a temporary moratorium on requests for research purposes due to staffing shortages. Jerrett’s team has been waiting 18 months for the requested samples.

“We really feel like the community deserves answers,” Jerrett said. “They’re the ones that are living with these risks, and they’ve been very adamant that they want us to look at clinical and biological markers. We’re trying to deliver as much of that as we can.”

Cover photo:  A view of the Porter Ranch area of Los Angeles on Jan. 8, 2016, where natural gas had been leaking from the Aliso Canyon storage facility since Oct. 23, 2015. Credit: Ted Soqui/Corbis via Getty Images

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