Levels of a cancer-causing air pollutant in a heavily industrialized region of Louisiana are much higher than previous estimates, according to new research.
Ethylene oxide is a gas used for chemical manufacturing and medical-grade sterilization that some industrial facilities release into the air as a by-product. Long-term exposure to the chemical increases the risk of multiple types of cancer, including leukemia, lymphoma, and breast cancer. It’s a huge concern for residents living in a stretch of southeastern Louisiana between Baton Rouge and New Orleans dubbed “Cancer Alley.”
But ethylene oxide is difficult to measure, and there’s a dearth of reliable data showing just how much is actually in the air.
A new study published in Environmental Science and Technology is the first to provide real-time, high-resolution measurements in southeastern Louisiana. In some places, levels of the chemical were as much as a thousand times higher than what the EPA considers safe.
The levels the group found are “appalling,” said Anne Rolfes, director of Louisiana Bucket Brigade, a nonprofit organization working to reduce pollution from the petrochemical industry in Louisiana.
“It’s Really Cool That These Instruments Exist”
Scientists have traditionally measured concentrations of ethylene oxide by capturing air in large steel canisters, then later analyzing the components of those air samples.
“New measurement technologies really needed to be utilized.”
But recent research has shown that such methods may not be reliable because the surface of the canisters seems to interact with and change concentrations of ethylene oxide and other gases. As a result, useful data on ethylene oxide are virtually nonexistent, even in places that most need these measurements, such as southeastern Louisiana, said Ellis Robinson, an air quality scientist at Johns Hopkins University and coauthor of the new study.
“We really didn’t have any good measurement data on it,” said Peter DeCarlo, an atmospheric scientist at Johns Hopkins University and coauthor of the new study. “New measurement technologies really needed to be utilized.”
Instead of using steel canisters, the research team attached two recently developed spectrometers to vehicles. They drove these mobile laboratories along a 70-mile (113-kilometer) route between New Orleans and Baton Rouge 23 times in February 2023. The instruments collected real-time chemical composition data on a parts per trillion scale.
“It’s really cool that these instruments exist and we can do this,” DeCarlo said.
Quantifying Air Quality
The EPA estimates that long-term exposure to concentrations of ethylene oxide over 11 parts per trillion is harmful to human health.
In the new study, the team found levels exceeding that threshold virtually everywhere along the route. In every census tract the team measured, ethylene oxide levels were higher than estimates from the EPA’s 2019 Air Toxics Screening Assessment, which is a modeling tool that simulates the distribution of air pollutants on the basis of the National Emissions Inventory, a database of air pollution emissions at the census tract level compiled from state, local, and tribal air agencies. The National Emissions Inventory is updated every 3 years. The EPA does not have any on-the-ground ethylene oxide measurements from the region.
In some places, the concentration of ethylene oxide the research team measured was up to 10 times higher than EPA estimates. That’s concerning for public health, DeCarlo said. Close to industrial facilities, levels were as high as 40 parts per billion—more than a thousand times higher than the EPA’s threshold.
The differences between EPA estimates and the study team’s measurements make a “very strong case for continuing to take measurements like this to better characterize ambient air,” said Elisabeth Galarneau, an air quality research scientist at Environment and Climate Change Canada who was not involved in the new study. “These high-resolution measurements for ethylene oxide are really fundamentally changing our understanding of ambient concentrations,” she explained.
The new findings could differ from EPA’s estimates for various reasons. It’s possible that the concentrations of ethylene oxide that the team measured in February aren’t entirely representative of ethylene oxide concentrations throughout the year. And because the team was limited to sampling on roadways, the concentrations may not represent levels of the chemical that would be found on farm fields or at industrial sites where road access is limited.
However, the team analyzed the spatial and temporal biases in their data, found that they were minimal, and determined that a more likely explanation for the discrepancy is that there are inaccuracies in the data that the EPA’s modeling tool is based on, DeCarlo and Robinson said.
Emissions and Effects
Using their data and a different EPA risk assessment tool called the Risk-Screening Environmental Indicators (RSEI) model, the team evaluated the health risks posed by ethylene oxide in the area. The RSEI model considers emissions data from the EPA’s Toxics Release Inventory as well as the toxicity properties of more than 400 chemicals.
“What it tells us is how important it is to reduce those emissions of ethylene oxide.”
The research team estimated that ethylene oxide is responsible for 68% of the total health hazards posed by industrial facility air emissions in the region, mainly stemming from the chemical’s carcinogenic traits.
“That’s an enormous fraction of the total hazard,” DeCarlo said. “What it tells us is how important it is to reduce those emissions of ethylene oxide.”
The EPA has taken recent action to lower such emissions: In March, the agency announced a rule tightening standards for nearly 90 commercial facilities nationwide that use and emit the chemical. The agency estimates that the rule will reduce cancer risk from ethylene oxide by about 90%. “The agency will continue to work closely with advocates and affected community members to ensure those lived experiences along with science and data informs our efforts to protect overburdened communities,” Shayla Powell, a representative for the EPA, wrote in an email.
The new study shows that laws and safety levels aren’t having their intended effect, though, Rolfes said. She added that she wants the EPA and Louisiana Department of Environmental Quality (LDEQ), which is responsible for air quality monitoring in the state, to take the lead on more on-the-ground measurements of ethylene oxide. LDEQ declined to comment for this story.
—Grace van Deelen (@GVD__), Staff Writer
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