Two toxic contaminants present in California’s ambient air appear to be much stronger carcinogens than previously known, state environmental health officials announced Thursday.
The draft finding from the state’s Office of Environmental Health Hazard Assessment says that acrolein and ethylene oxide may pose an estimated cancer risk more than 10 times higher than benzene, a serious carcinogen linked to leukemia and other cancers.
It is the first step in a review process before final risk values are adopted, and it arrives at a time federal air-quality regulations are being reined in.
“If the early air monitoring results bear out, and if the draft cancer values developed are close to what eventually becomes final, then each air contaminant poses an unacceptable cancer risk,” said Kris Thayer, OEHHA’s director.
The update reflects the state’s evolving understanding of its most dangerous pollutants, which has shifted over the decades from visible pollutants, such as smog, to more invisible ones that cause cancer, heart disease and other health harms.
It comes only two months after the Trump administration’s Environmental Protection Agency moved to roll back standards on ethylene oxide, or EtO, in an effort to save millions of dollars in compliance costs for facilities that use the chemical for medical sterilization. The administration said it acted to “safeguard the supply of essential medical equipment,” but experts said the move will also expose more people to health risks.
It also follows a new national report from the American Lung Assn. that found 82% of Californians live in counties with unhealthful air, nearly double the national average.
“This is an important step to better understanding the harms of pollutants impacting Californians’ health,” said Will Barrett, assistant vice president for nationwide clean air policy at the American Lung Assn., who reviewed the state’s findings for The Times. “Following the latest available health science to determine risk is crucial to protecting health.”
Ethylene oxide is a colorless gas often used in the sterilization of medical devices, particularly those that can’t be cleaned using steam or radiation.
Acrolein can be formed when materials burn, such as cigarettes, e-cigarettes and vapes, wood, plastics and gasoline for cars, trucks, ships and aircraft. It can also be released by cooking fats and oils at high temperatures, and has been found in water produced by oil and gas operations and is an ingredient in some pesticides used in irrigation canals.
People can take steps to protect themselves from acrolein exposure in everyday life by avoiding smoking tobacco or using e-cigarettes and vaping products, avoiding smoke from fires or exhaust from diesel and gasoline vehicles and equipment — much of which can also help reduce exposure to ethylene oxide, officials said. When cooking with oils or fats, people should avoid very high temperatures and use a range hood fan when possible.
While both chemicals have been present in the state’s air for years, the new assessments from OEHHA are based on the latest science on health risks, officials said. Both acrolein and ethylene oxide were found to pose an estimated cancer risk exceeding 800 in 1 million — on par with the cancer risk that diesel exhaust was estimated to pose when it first emerged as a major public health concern in the 1990s, the agency said.
In response to the findings, Gov. Gavin Newsom’s May budget revision, released Thursday, includes $2.5 million in funding for the California Air Resources Board and OEHHA in support of research to help reduce people’s exposure to acrolein and ethylene oxide. The funding will help the state identify and track major sources of the chemicals and turn the findings into public health policy outcomes, officials said.
OEHHA’s assessment provides the first cancer risk value for acrolein since it was classified as probably cancer-causing to humans by the International Agency for Research on Cancer in 2020. Ethylene oxide was already identified as a carcinogen by the state, but the new assessment updates its risk levels based on the new research. The risk calculations are based on air monitoring data, which vary across the state depending on location, nearby sources and other factors.
Officials said the findings underscore the state’s efforts to strengthen environmental protection measures for residents at a moment when federal officials seek to loosen them.
“Especially in light of some of the national rollbacks we’re seeing on protections for public health, it really underscores how important the work that we’re doing here in California is,” said Courtney Smith, principal deputy executive officer with the Air Resources Board. “Not only for protecting the health of Californians, but also to ensure that there is rigorous, solid science available to other entities as well who may want to pursue additional protections.”
On Friday, California Atty. Gen. Rob Bonta joined a multi-state coalition in a letter opposing the EPA’s plan to roll back national standards for EtO emissions. “The science is clear” about its risks, Bonta said in a statement.
“Communities of color and low-income communities are disproportionally impacted because commercial sterilization facilities are more likely to be located in their neighborhoods,” Bonta said. “No community should have to live with this exposure, and we urge the Trump administration to reverse course immediately and continue to implement strong health protections and oversight of ethylene oxide use.”
Short-term exposure to EtO by inhalation can cause headaches, dizziness, nausea, fatigue respiratory irritation and other adverse health effects, according to the federal Agency for Toxic Substances and Disease Registry. Longer-term exposure increases the risk of cancers of the white blood cells, such as non-Hodgkin’s lymphoma, as well as breast cancer.
Inhaling acrolein can cause nose and throat irritation and a decreased breathing rate. Chronic exposure, such as through cigarette smoke, has been linked to the development of asthma, chronic obstructive pulmonary disease and respiratory cancers.
The findings also come as California continues to receive poor grades on air quality. The American Lung Assn. annual State of the Air report found that the five U.S. counties with the worst smog pollution are all in California. Bakersfield was the metropolitan area with the worst level of year-round particle pollution for the seventh year in a row, while Los Angeles was the city with the worst ozone pollution, as it has been for 26 of the last 27 years.
“Californians face the most significant smog and soot challenges in the nation, but our air agencies have followed the science to build policies and programs to make real headway,” Barrett said. The state’s latest assessment “speaks to the need for ongoing local efforts while the federal government ignores the science and opens the door for more pollution. California must continue to invest in things like cleaning up truck fleets, broader public education and the underlying science to guide policies to protect health.”
Thursday’s announcement kicks off a 45-day public comment period, after which the draft assessments may be revised before undergoing additional public comment, peer review by the state’s Scientific Review Panel on Toxic Air Contaminants, and eventual adoption.
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Hayley Smith
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