– Neighbors used to barely notice the drab, low-slung industrial building across the river from downtown. The only concern was word years ago about a gas used inside being explosive enough to level the building.

Even after the Environmental Protection Agency concluded that the gas is responsible for some of the nation’s biggest cancer risks from toxic air pollution, it was months before residents knew they had an ethylene oxide problem.

EPA scientists had determined the lifetime cancer risk in one Grand Rapids census tract is nearly four times greater than the national average. But the Trump administration buried the finding in a report quietly released in 2018.

Nobody at the EPA told people in the middle- and working-class neighborhood known as Kielbasa Valley that they were potentially at risk. Nor did the agency investigate the facility that had reported emitting the cancer-causing gas: a medical device manufacturer.

“It’s like we’ve been forgotten. Or maybe they just don’t care,” said Lorna Conkle, who lives a block from the facility.

More than a half million Americans exposed to toxic air pollution face cancer risks exceeding agency guidelines, EPA data said. Ethylene oxide is the chief chemical of concern.

Yet facilities emitting the toxic gas operate under federal regulations that haven’t been updated to reflect the risk it poses. As a result, neighbors for the most part don’t know they are breathing pollution that can potentially trigger breast cancer, leukemia and lymphomas.

Some of the communities the EPA found to be at risk are near sprawling petrochemical complexes in Louisiana and Texas where ethylene oxide is produced by industry giants, including Dow Chemical, Shell, Huntsman and Union Carbide (now a subsidiary of Dow). Others live close to nondescript buildings owned by lesser-known companies that use the toxic gas to sterilize medical products.

The only source of ethylene oxide scrutinized by the EPA is Sterigenics, a sterilization facility in Willowbrook, a Chicago suburb where residents and officials demanded action after learning they were living in a pollution hot spot.

Faced with a public outcry and bipartisan pressure, the EPA deployed air monitoring equipment at parks, schools and homes near Sterigenics. Three months of testing confirmed that pollution from the facility could trigger more than 10 cases of cancer for every 10,000 people exposed during their lifetimes — a rate 10 times higher than what the EPA considers acceptable.

“We have been very proactive,” said Cathy Stepp, the Trump administration’s top EPA official in the Midwest.

However, federal officials have refused to monitor air quality in other communities that stand out in the National Air Toxics Assessment, a report compiled by EPA scientists. There are 73,057 census tracts in the U.S., with 2,500 to 8,000 people in each one. In 106 tracts, the data show, the risk of developing cancer from breathing toxic air pollution over a lifetime exceeds agency guidelines. Three entire counties in Louisiana face risks considered unacceptable.

The EPA didn’t require the sterilization industry to install pollution-control equipment until the late 1990s. Agency officials relaxed the regulations a few years later in response to explosions at plants in Indiana, Massachusetts, Virginia and Wisconsin. Industry representatives persuaded regulators that the controls were responsible for the blasts, though investigators found operator errors were to blame.

Cabinet members, including EPA Administrator Andrew Wheeler, are under White House pressure to eliminate regulations, not to adopt new ones. Trade groups have petitioned the administration to throw out the EPA’s scientific evaluation, hiring industry-friendly scientists whose research was rejected by two panels of independent scientists convened by the EPA.

If administration officials agree with industry lobbyists, the government would not require companies that make and use ethylene oxide to reduce their pollution.

“People are going to continue to suffer,” said Jennifer Sass, a senior scientist at the nonprofit Natural Resources Defense Council. “A bunch of corporations are having a temper tantrum because they don’t like what the science is telling us about this extremely dangerous chemical.”