For decades, a small program in the Environmental Protection Agency conducted the painstaking scientific work of assessing the toxicity of chemicals. 

The calculations done by scientists at IRIS, as it was commonly known, underpin vast numbers of chemical regulations, permits and other environmental rules in the U.S. and abroad.

Now the Trump administration is suggesting that their library of more than 500 chemical assessments can’t be trusted, opening the door to weakening hundreds of efforts to protect people from harmful chemicals at the state and federal level. The second-guessing could extend even to long-settled standards, environmental scientists said, such as how much arsenic is allowed in drinking water and how much lead is acceptable in paint and soil.

In an internal memo obtained by ProPublica, David Fotouhi, the deputy administrator of the agency, sharply criticized IRIS this week and directed EPA offices that have used any of the chemical assessments the program has produced to review them. He also advised “external entities” that have used the IRIS assessments to consider undertaking similar reviews and cautioned against using them in future regulations.

The six-page memo said the EPA would be adding “disclaimer language” to the website of the program — the Integrated Risk information System — stating that its toxicity findings are not necessarily meant to be used in regulation.

“This creates the opportunity for companies that pollute to push back on rules and regulations they don’t like,” said Robert Sussman, an attorney who has worked for chemical companies and environmental groups as well as the EPA. “Anybody who wants to ignore a regulation, permit or enforcement action can now just point to this memo and say the IRIS number it was based on wasn’t valid. It’s a huge setback for the process of protecting people from chemicals.” 

Fotouhi’s memo echoes industry criticism that the program’s scientists are far too conservative in gauging the toxicity of chemicals. Before President Donald Trump appointed him as the second highest official at the EPA, Fotouhi worked as a lawyer representing companies accused of causing toxic pollution. 

In an emailed statement, the EPA press office wrote that Fotouhi has complied with all applicable government ethics obligations and said his directive would not put people at risk or allow anyone to ignore environmental regulations. Any revisions to permits or regulatory standards must go through a process that includes public participation, the office noted.

“Science is at the heart of the Agency’s work, and this memo reaffirms that point clearly and unequivocally,” the press office wrote. 

The EPA created IRIS in 1985 as the nation’s clearinghouse for information on the toxicity of chemicals. Its assessments quantify the highest safe level of exposure to a chemical before it triggers health effects, including, in many cases, cancer. The agency previously prided itself on the program’s impartiality and, in an effort to protect its science from the influence of industry, purposefully kept the program separate from the agency offices that craft regulation. 

The memo now tasks those offices with conducting toxicity assessments and brings an end to the program that has powered the EPA’s efforts to protect people from harmful chemicals. 

IRIS assessments earned a reputation for being extremely detailed and undergoing numerous rounds of review by many scientists. The EPA offices routinely relied on them to set the amount of a particular chemical that industrial facilities are allowed to emit. States use IRIS assessments to decide which chemicals deserve their immediate attention and to calculate limits in rules and regulations. And IRIS reports guide environmental regulation in countries that don’t have the resources to fund their own scientists to review chemicals.

The memo is the latest attack on the program. The Heritage Foundation’s Project 2025 called 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.” And last year, congressional Republicans introduced industry-backed legislation that would prevent the EPA from using IRIS assessments in environmental rules, regulations, enforcement actions and permits. (The bills were not put to a vote.) 

IRIS 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.

Still, IRIS’ work stood 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. 

Over the past year, the EPA has essentially shut down IRIS by reassigning most of the dozens of the scientists who worked in the program to other parts of the agency. And the administration has refused to publish a report on a “forever chemical” known as PFNA, which was completed by IRIS in April 2025. 

But, until now, the EPA had not challenged the science in IRIS assessments. The memo changes that. Although the agency will continue to post the documents on its website, it calls their validity into question, arguing that the toxicity levels calculated in IRIS reports are overly cautious and fail to include the perspective of all “stakeholders.” 

This approach produces values that are more protective than they need to be, according to Fotouhi. “When many conservative assumptions are stacked on top of each other, the cumulative effect can produce an estimated ‘safe’ exposure level that is orders of magnitude below naturally occurring levels in the environment,” he wrote.

Fotouhi pointed specifically to ethylene oxide, a chemical used to sterilize medical equipment — and one used by Medline, a company he used to represent as an attorney at the firm Gibson, Dunn & Crutcher, according to financial statements he filed and that are contained in ProPublica’s database of Trump administration officials’ disclosures. IRIS updated its assessment of ethylene oxide in 2016, after it reviewed the medical literature and found that the chemical was a more potent carcinogen than previously believed. 

The EPA’s updated cancer risk estimate set off waves of concern — and lawsuits — in communities around the country where people are highly exposed to the chemical. And it led the Biden administration to issue more protective regulations. Companies that use or manufacture ethylene oxide and their representatives complained to the EPA and questioned the science that cost them so dearly. 

Under Trump, the agency, which has been championing industry, has already paused those efforts to protect the public from ethylene oxide. But this latest step, which threatens to destabilize health protections built on hundreds of IRIS assessments, is a boon to countless companies emitting a huge variety of toxic chemicals, according to Maria Doa, a scientist at the Environmental Defense Fund who spent more than 20 years working on chemical regulation at the EPA.

“This is the EPA adopting the industry’s talking points,” Doa said. “And it’s going to leave a lot of people at risk.”