For decades, Republican lawmakers and industry lobbyists have tried to chip away at the small program in the Environmental Protection Agency that measures the threat of toxic chemicals.

Most people don’t know IRIS, as the program is called, but it is the scientific engine of the agency that protects human health and the environment. Its scientists assess the toxicity of chemicals, estimating the amount of each that triggers cancer and other health effects. And these values serve as the independent, nonpartisan basis for the rules, regulations and permits that limit our exposure to toxic chemicals.

Now IRIS faces the gravest threat to its existence since it was created under President Ronald Reagan four decades ago.

Legislation introduced in Congress would prohibit the EPA from using any of IRIS’ hundreds of chemical assessments in environmental rules, regulations, enforcement actions and permits that limit the amount of pollution allowed into air and water. The EPA would also be forbidden from using them to map the health risks from toxic chemicals. The bills, filed in both the U.S. Senate and House of Representatives earlier this year, are championed by companies that make and use chemicals, along with industry groups that have long opposed environmental rules. If it becomes law, the “No IRIS Act,” as it’s called, would essentially bar the agency from carrying out its mission, experts told ProPublica.

“They’re trying to undermine the foundations for doing any kind of regulation,” said William Boyd, a professor at UCLA School of Law who specializes in environmental law. Boyd noted that IRIS reports on chemicals’ toxicity are the first step in the long process of creating legal protections from toxic pollutants in air and water.

“If you get rid of step one, you’re totally in the dark,” he said.

If the act passes, companies could even use the law to fight the enforcement of environmental rules that have long been on the books or permits that limit their toxic emissions, environmental lawyers told ProPublica.

The attack on IRIS has a good chance of succeeding at a time when Republicans are eager to support President Donald Trump’s agenda, according to environmental advocates who monitor Congress. The bills dovetail with the anti-regulatory efforts that have marked the second Trump administration, which has begun to dismantle climate protections, nominated industry insiders to top positions in the EPA and announced plans for unprecedented cuts that could slash the agency’s budget by 65%.

Project 2025, the ultraconservative playbook that has guided much of Trump’s second presidency, calls for the elimination of IRIS on the grounds that it “often sets ‘safe levels’ based on questionable science” and that its reviews result in “billions in economic costs.” The policy blueprint echoes industry claims that IRIS does not adequately reflect all of the research on chemicals; there are sometimes significant differences between the program’s conclusions and those of corporate-funded scientists.

IRIS has long been a target of industry and has at times been criticized by independent scientific bodies. More than a decade ago, for example, the National Academies of Sciences, Engineering, and Medicine took issue with the organization, length and clarity of IRIS reviews; a more recent report from the same group found that IRIS had made “significant progress” in addressing the problems.

IRIS’ work stands out in a world where much of the science on toxic chemicals is funded by corporations with a vested stake in them. Studies have shown that industry-funded science tends to be biased in favor of the sponsor’s products. But IRIS’ several dozen scientists do not have a financial interest in their findings. Their work has had a tangible impact on real people. The program’s calculations are the hard science that allow the agency to identify heightened disease risk due to chemicals in the air, water and land. And these revelations have, in some cases, led to stricter chemical regulations and grassroots efforts to curtail pollution.

“Bitter Battles”

IRIS, which stands for Integrated Risk Information System, was created in 1985. Until that point, different parts of the EPA had often assessed chemicals in isolation, and their methods and values were not always consistent.

At first, IRIS just collected assessments completed by various divisions of the EPA. Then, in 1996, it began conducting its own, independent reviews of chemicals. Its scientists analyze studies of a chemical and use them to calculate the amount of the substance that people can be exposed to without being harmed. IRIS sends drafts of its reports to multiple reviewers, who critique its methods and findings.

As the tranche of assessments grew, so did its value to the world. States began relying on IRIS’ numbers to set limits in air and water permits. Some also use them to prioritize their environmental efforts, acting first on the chemicals IRIS deems most harmful. Countries that don’t have the expertise to assess chemicals themselves often adopt IRIS values to guide their own regulations.

Today, IRIS’ collection of more than 500 assessments of chemicals, groups of related chemicals, and mixtures of chemicals is the largest database of authoritative toxicity values in the world, according to Vincent Cogliano, a recently retired scientist who worked on IRIS assessments for more than 25 years.

From the beginning, industry scientists challenged IRIS with calculations that showed their chemicals to be less dangerous.

“There were a lot of pretty bitter battles,” said Cogliano, who remembers particularly intense opposition to the assessments of diesel engine exhaust and formaldehyde during the 1990s. Critiques of IRIS assessments intensified over the years and began to slow the program’s work. “It took so long to get through that there were fewer and fewer assessments,” said Cogliano.

In 2017, opposition to IRIS escalated further. Trump’s budget proposal would have slashed funding for the program. Although Congress funded IRIS and the program survived, some of its work was halted during his first presidency. Trump appointed a chemical engineer named David Dunlap to head the division of the EPA that includes IRIS. Dunlap had challenged the EPA’s science on formaldehyde when he was working as the director of environmental regulatory affairs for Koch Industries. Koch’s subsidiary, Georgia-Pacific, made formaldehyde and many products that emit it. (Georgia-Pacific has since sold its chemicals business to Bakelite Synthetics.) While Dunlap was at the EPA, work on several IRIS assessments was suspended, including the report on formaldehyde. IRIS completed that report last year.

That assessment proved controversial, as ProPublica documented in its investigation of the chemical late last year. In calculating the risks that formaldehyde can cause cancer, IRIS decided not to include the chance that the chemical can cause myeloid leukemia, a potentially fatal blood cancer. The EPA said IRIS made this decision because it lacked confidence in its calculation; the agency admitted that the omission drastically underestimated formaldehyde’s cancer risk.

“The Depth of the Poisoning”

Still, some of IRIS’ assessments have made a huge difference in parts of the country.

In 2016, IRIS updated its assessment of a colorless gas called ethylene oxide. The evaluation changed the chemical’s status from a probable human carcinogen to plainly “carcinogenic to humans.” And IRIS calculated the uppermost amount of the chemical before it starts to cause cancer, finding that it was 30 times lower than previously believed.

The EPA used that information to create a map, which showed that people living near a sterilizing plant in Willowbrook, Illinois, had an elevated cancer risk because the facility was releasing ethylene oxide into the air. Once locals learned of their risk, they kicked into action.

“That knowledge led us to be able to really activate the groundswell of community members,” said Lauren Kaeseberg, who was part of a group that held protests outside the plant, met with state and local officials, and testified at hearings. Not long after the protests, Illinois passed legislation limiting the release of the pollutant, the local plant shut down and the cancer-causing pollution was gone from the air.

Around the country, the pattern has been repeated. After IRIS issues its estimate of the amount of a chemical that people can safely be exposed to without developing cancer and other diseases, the EPA uses that information to map the threats from chemicals in air. IRIS’ evidence showing that people have an elevated risk of cancer has sparked some hard-hit communities to fight back, suing polluters, shuttering plants and demanding the offending chemical be removed from their environment.

In St. John the Baptist Parish, Louisiana, residents had long felt as if they had more than their share of sickness. The small rectangle of land near the Mississippi River abuts a chemical plant that emits foul-smelling gases. For decades, as they breathed in the fumes, residents suffered from respiratory problems, autoimmune diseases, cancers and other ailments. In 2016, after IRIS assessed the toxicity of chloroprene, one of the chemicals coming out of the plant’s smokestacks, the people of St. John discovered the main source of their problems. The IRIS assessment showed that chloroprene was a likely carcinogen and caused damage to the immune system. With this information, the EPA concluded that St. John had the highest cancer risk from air pollution in the country.

“I didn’t realize the depth of the poisoning that was taking place until EPA came to our community in 2016 and brought us that IRIS report,” said Robert Taylor, who has lived his entire life in St. John. When the agency representatives arrived, Taylor’s wife had cancer and his daughter was bedridden with a rare autoimmune condition. A lifelong musician who was then 75, Taylor began organizing his neighbors to demand a stop to the deadly pollution. (His wife died in December.)

The assessments of chloroprene and ethylene oxide — and the activism they sparked around the country — eventually led the EPA to crack down. Last year, the agency announced several rules that aimed to reduce toxic emissions. The rules call for changes in how companies produce and release chemicals — the type of reforms that can be expensive to undertake.

The Biden administration sued Denka, the company that owns the chloroprene-releasing plant in St. John, in an effort to force it to curb the amount of the chemical it released. But the Trump administration intends to drop that suit, according to The New York Times.

For its part, Denka sued the EPA over one of the rules in July, asking the court for more time to implement the changes. The company argued that the agency was on a “politically motivated, unscientific crusade” to shut down the plant.

Critics of IRIS have used similarly barbed language in their recent attacks. In his press release introducing what he calls the “No Industrial Restrictions in Secret Act” in the House, Rep. Glenn Grothman, R-Wis., wrote that “Unelected bureaucrats in the Biden Administration have disrupted the work of Wisconsin’s chemical manufacturers and inhibited upon the success of the industry through the abuse of the EPA’s IRIS program.” The press release said the bill is supported by Hexion, which has a plant in his district. Hexion makes formaldehyde, a chemical that increases the cancer risk nationwide.

Neither Grothman nor Sen. John Kennedy, R-La., who introduced the Senate version of the bill, responded to questions from ProPublica, including how they think the EPA could regulate chemicals if the bill passes. The EPA did not answer questions for this story.

The American Chemistry Council, which represents more than 190 companies, sent a letter to Lee Zeldin in late January calling on the EPA administrator to disband IRIS and prohibit the use of its assessments in rules and regulations. IRIS “has been increasingly used to develop overly burdensome regulations on critical chemistries,” the letter states, going on to argue that the program lacks transparency and “has often fallen short of scientific standards.” (The letter was first reported by Inside EPA.) The American Petroleum Institute, the Extruded Polystyrene Foam Association, the Independent Lubricant Manufacturers Association, the Fertilizer Institute and the Plastics Industry Association were among the dozens of organizations representing industries financially impacted by IRIS’ chemical assessments that signed the letter.

“Off the Deep End”

Industry groups have also criticized IRIS for being slow and overstepping its authority. And they have noted that outside organizations have found fault with it.

In addition to the National Academies criticism in 2011 about the clarity and transparency of its reports, IRIS has responded to recommendations from the Government Accounting Office, according to a report the congressional watchdog issued last week. The GAO, which monitors how taxpayer dollars are spent, placed IRIS on its “high risk list” in 2009. But the GAO did so not because it was vulnerable to waste, fraud and abuse — the reasons some programs land on the list — but because the watchdog decided IRIS wasn’t doing enough assessments of dangerous chemicals. Since 2009, the GAO made 22 recommendations to IRIS, all of which have been implemented, according to the agency’s website. The new report acknowledged improvements but noted that the program’s current pace of finalizing assessments “likely cannot increase without more resources.” According to the GAO report, in 2023 and 2024, IRIS had reported needing 26 additional staff members to meet the demand for chemical assessments.

Defenders of the program say the criticisms mask a simple motive: protecting industry profits rather than public health.

“It’s blatant self-interest,” said Robert Sussman, a veteran attorney who worked at the EPA as well as for environmental groups and chemical companies. “What they’re really trying to do here is prevent the EPA from doing assessments of their chemicals.”

While he has witnessed many attempts to scale back the EPA’s power in his 40-year career, Sussman described the current effort to eliminate its use of IRIS’ chemical assessments as “completely off the deep end.”

Weaker bills targeting IRIS were introduced into both the House and Senate in February of last year but did not have the political support to advance. Now, after the election, the possibility of success is entirely different, according to Daniel Rosenberg, director of federal toxics policy at the Natural Resources Defense Council, an environmental nonprofit.

“I don’t think there’s any doubt that if it does pass Congress — and it now could — the president will sign it,” said Rosenberg. But Rosenberg added that he believes that if the public understood the consequences of doing away with the science at the core of the EPA’s work, people could potentially sway their lawmakers to stand up to the attack on IRIS.

“The current political alignment is clearly very favorable to the chemical lobby, but their actual agenda has never been popular,” said Rosenberg. “There’s never been a case where people are in favor of more carcinogens in their environment.”