Leaked EPA Memo Targets IRIS Chemical Database, Risk Assessments for 500+ Substances Under Review

The Trump administration's Environmental Protection Agency is questioning the scientific validity of more than 500 chemical toxicity assessments compiled over decades by the IRIS program, according to an internal memo obtained by ProPublica. The move signals a potential effort to dismantle the scientific foundation underpinning hundreds of federal and state environmental regulations governing chemical safety. EPA Administrator Lee Zeldin is spearheading the review, which critics warn could unravel decades of settled risk science relied upon by regulators across the country.

IRIS, the Integrated Risk Information System, has for years conducted the painstaking scientific work of calculating how much exposure to chemicals like arsenic, lead, and industrial solvents harms human health. These assessments form the backbone of enforceable standards governing everything from drinking water contaminants to acceptable levels of toxic metals in soil. The internal memo suggests the Trump administration views the existing library of assessments as untrustworthy, raising the prospect of reopening long-settled standards—including those for arsenic in drinking water and lead in paint—that have guided cleanup efforts and enforcement actions for years.

The directive places significant pressure on state environmental agencies, many of which have built their own chemical safety frameworks around EPA's IRIS assessments. International regulators also frequently cite IRIS evaluations when setting their own standards. Scientists warn that reexamining assessments that underwent rigorous peer review could delay critical regulatory actions, create uncertainty for industries operating under existing permits, and shift the burden of proof regarding chemical safety onto affected communities. The EPA has not yet specified which specific regulations might be revisited or on what timeline.