Is it time to crack down on ethylene oxide emissions?

Ethylene oxide is a basic chemical building block for a slew of modern products, including plastics and medicines. This seven-atom molecule is the simplest epoxide. But not much is simple in the debate over how much of this flammable gas—which is carcinogenic when inhaled—is safe for the public to breathe.

The issue is coming to a head now because the US Environmental Protection Agency is under a court-imposed deadline to revise, by early next year, regulations on hazardous air pollution for plants that manufacture ethylene oxide.

On one side of this controversy are makers of ethylene oxide. They have found a partner in the Texas Commission on Environmental Quality (TCEQ) to support their assertion that the gas is a far less potent carcinogen than the EPA concluded in 2016. Texas is home to 5 of the nation’s top 10 emitters of ethylene oxide, according to 2017 chemical release data, the most recent information available.

On the other side are environmentalists, community activists, and some federal and state lawmakers who are relying on the EPA’s externally peer-reviewed scientific analysis of ethylene oxide’s hazards. Regulation based on this analysis would likely require makers of the substance to ratchet down their emissions significantly.

Made from petroleum or natural gas, ethylene oxide is a key material in the manufacture of plastics, glycols, detergents, solvents, adhesives, and pharmaceuticals. It is also used as a pesticide to fumigate spices. In addition, commercial sterilization companies use ethylene oxide to render medical devices free of germs.

The chemical sector accounted for more than three-quarters of the 2017 nationwide emissions of ethylene oxide, as reported to the EPA under the community right-to-know law. That year, chemical and plastics manufacturers released 84 metric tons (t) of the chemical at 71 facilities, nearly half of which are in Texas or Louisiana.

Most ethylene oxide from chemical and plastics plants moves into the atmosphere through chimneys, stacks, or vents, says Neil Carman, clean air director at the Sierra Club’s Lone Star Chapter. But a significant amount also leaks from pumps, valves, and other pressurized connections, adds Carman, a former air pollution inspector in Texas. Data reported to the EPA show that about 27%, or 23 t, of ethylene oxide released from these facilities in 2017 consisted of these fugitive emissions.

According to the American Chemistry Council (ACC), which lobbies on behalf of chemical manufacturers, 15 of the sites are ethylene oxide production facilities owned by nine companies. Ethylene oxide production involves more than 45,000 jobs and pours about $3.5 billion in direct value into the US economy, the ACC says.

At the same time, communities of color and low-income neighborhoods have disproportionately high levels of exposure to ethylene oxide from industrial facilities, the EPA’s National Environmental Justice Advisory Council says in a May letter to the agency. The advisory group urged the agency to decrease emissions of the gas to protect public health.

The EPA is under a court order to decide by March 13, 2020, whether and how much to tighten existing emission limits for hazardous air pollutants, including ethylene oxide, from manufacturers of miscellaneous organic chemicals. Those standards were finalized in 2006.

The EPA’s 2018 National Air Toxics Assessment also points to the need to address ethylene oxide emissions. Federal and state regulators use this risk-based assessment as a screening tool to identify areas, pollutants, or polluters for further scrutiny. The most recent results, made on the basis of emission data from 2014, indicated that lifetime cancer risk in some US census tracts was significantly higher than the national average. Those tracts collectively are home to half a million people.

For ethylene oxide pollution specifically, the assessment says that the gas is “a potential concern” in several parts of the US. “Based on an examination of available data, EPA does not expect ethylene oxide levels in the air in these areas to be high enough to cause immediate harm to health,” the agency says on a web page dedicated to the chemical.

But over time, people breathing in ethylene oxide pollution could develop health woes, the EPA warns.

“Long-term exposure to ethylene oxide can irritate the eyes, skin, nose, throat, and lungs, and harm the brain and nervous system,” leading to problems including headaches, memory loss, and numbness, the EPA says separately from the assessment. “Studies show that breathing air containing elevated ethylene oxide levels over many years increases the risk of some types of cancers.” These include white-blood-cell cancers such as non-Hodgkin’s lymphoma, myeloma, and lymphocytic leukemia, as well as breast cancer, the agency says.

The National Air Toxics Assessment relied on an EPA hazard analysis for ethylene oxide done in 2016. In that analysis, the agency classified the chemical as a human carcinogen because of studies that found increased risk of white-blood-cell cancers in workers exposed to the chemical. That hazard analysis determined that there is a one-in-a-million chance of developing cancer from inhaling 0.1 parts per trillion (ppt) of ethylene oxide over a lifetime. How that 0.1 ppt value would translate into rules under the Clean Air Act is unclear because the EPA regulates hazardous air pollutants like ethylene oxide by requiring installation of the maximum emission controls available.

The ACC, the chemical manufacturers’ group, is attacking the 0.1 ppt number, calling it “overly conservative . . . to the point of absurdity.” In part, the ACC argues that estimates of historical exposures of workers to ethylene oxide were inaccurate. In a September 2018 letter to the EPA, the ACC asked the agency to withdraw the National Air Toxics Assessment’s cancer-risk estimates for ethylene oxide and to revise them with “scientifically-supportable risk values.” The EPA hasn’t yet responded to the ACC’s request.

Environmental advocates disagree with the ACC’s position.

“EPA scientists reached a well-supported conclusion on the potent cancer risk from this air pollutant after a multiyear process and independent peer review,” says Emma Cheuse, an attorney for the nonprofit environmental law group Earthjustice. “EPA has no scientific reason to try to ignore the evidence of cancer risk from ethylene oxide.”