GAO Spotlight Pushes Microplastics Into Federal Policy Focus as Health Risks Remain Unclear

A new Government Accountability Office spotlight is putting microplastics squarely on the federal agenda, reflecting growing concern across Washington that tiny plastic particles may pose a public health and environmental risk even as scientists still cannot say how much typical human exposure harms people.

In its two-page report released Tuesday, “Science & Tech Spotlight: Microplastics in the Body and Environment,” the GAO said more than 24 million tons of plastic enter the environment worldwide each year. As larger plastic items break down, they form microplastics — particles smaller than 5 millimeters — and nanoplastics, which are smaller than 1 micrometer. The report points to major sources including vehicle tires, synthetic fabrics, plastic bottles and paint. Smaller particles can be inhaled, ingested or absorbed through the skin, and can enter organs, blood and cells, the GAO said.

What that means for human health is still unsettled. The GAO said exposure to microplastics is associated with health problems in humans and other organisms, but researchers have not determined the extent to which the particles actually cause those problems. One of the clearest human studies so far, published in 2024 in The New England Journal of Medicine, found that patients whose arterial plaques contained microplastics or nanoplastics had a higher risk of heart attack, stroke or death. But that study was observational, meaning it showed a correlation and did not prove the particles caused those outcomes.

That uncertainty helps explain the GAO’s main conclusion: the biggest gaps are not just in toxicology, but in basic measurement and removal. Current testing methods often require extensive laboratory sample preparation, making on-site detection difficult. Methods also are not fully standardized across laboratories, making results harder to compare. And while some technologies, such as reverse osmosis, can remove microplastics from water, the GAO said those approaches may be difficult or costly to scale for public drinking-water systems.

The report arrives as several federal agencies have taken steps this year that treat microplastics as an emerging issue worth closer study. On April 2, the Environmental Protection Agency added microplastics to its draft Sixth Contaminant Candidate List, or CCL 6, under the Safe Drinking Water Act. The list is EPA’s periodic inventory of unregulated contaminants that may warrant future attention. Inclusion can shape research and monitoring priorities and could inform later regulatory decisions, but it is not a drinking-water standard or final rule.

EPA Administrator Lee Zeldin said at the time that “by placing microplastics and pharmaceuticals on the Contaminant Candidate List for the first time ever, EPA is sending a clear message: we will follow the science, we will pursue answers, and we will hold ourselves to the highest standards to protect the health of every American family.”

Also on April 2, the Department of Health and Human Services, through its research arm ARPA-H, announced STOMP — short for Systematic Targeting Of MicroPlastics — a $144 million program aimed at developing ways to measure microplastics and nanoplastics in the human body, understand their effects and remove them. Alicia Jackson, director of ARPA-H, said in a statement: “Microplastics are in every organ we look at — in ourselves and in our children. But we don’t know which ones are harmful or how to remove them. Nobody wants unknown particles accumulating in their body. The field is working in the dark. STOMP is turning on the lights.”

The Agriculture Department followed on May 28 with the Great American Cotton Plan, a policy initiative promoting domestic cotton under a “Plant Not Plastic” message. The effort ties to concerns that synthetic fabrics shed microfibers, though it is a materials and agricultural push rather than a scientific finding about health effects.

Taken together, the actions show a federal response that is still centered on research, monitoring and possible future regulation, not settled conclusions or immediate nationwide standards. That reflects the science itself: much of the evidence on harmful effects comes from animal or laboratory studies, often at exposure levels higher than what people typically encounter, and agencies say standardized testing is still lacking. For now, Washington’s message is that microplastics are serious enough to measure more carefully — and still uncertain enough that the government is not yet ready to draw firm lines about everyday risk.