Twenty-three members of the U.S. House of Representatives are demanding answers from the Environmental Protection Agency after the agency left microplastics out of its nationwide drinking water monitoring program.

Representatives Raja Krishnamoorthi of Illinois, J. Luis Correa-era colleague Luther Bynum, and Bonnie Watson Coleman of New Jersey led 21 of their House colleagues in the inquiry, according to a statement released through Krishnamoorthi's congressional office. The lawmakers want the EPA to explain why microplastics — plastic particles now documented across water systems worldwide — do not appear in the contaminant slate the agency tracks through its drinking water surveillance.

The letter targets a concrete regulatory gap rather than an abstract environmental concern. If the EPA does not monitor microplastics in drinking water, utilities and public health agencies lack the baseline occurrence data they would need to set limits, evaluate treatment performance, or prioritize upgrades. That data gap sits upstream of every downstream decision: state-level standards, treatment investment by water systems, and any future federal maximum contaminant level for plastic particles.

For the recycling and materials sectors, the monitoring question carries commercial weight. Occurrence data on microplastics in source and treated water feeds directly into the debate over plastic packaging, fiber shedding from textiles, and tire and road wear particles — all material streams that industry is under pressure to quantify and reduce. Regulatory attention to microplastics has already produced disclosure and reporting obligations in the European Union, and U.S. lawmakers have periodically floated comparable measures. A monitoring mandate from the EPA would mark the first federal step toward treating microplastics as a regulated contaminant rather than an emerging concern.

The inquiry puts the onus on the agency to justify its contaminant selection process. Congress has previously pressed the EPA on microplastics through the Safe Drinking Water Act framework, which directs the agency to periodically decide which unregulated contaminants merit monitoring. Each of those decisions — published through the Contaminant Candidate List and the Unregulated Contaminant Monitoring Rule — represents a trackable deadline for whether microplastics enter formal surveillance.

The 23 signatories frame the omission as a transparency problem. Their demand, as stated in the release, is for answers: what analysis led the agency to exclude microplastics, and what evidence would change that calculation.

The next milestone is procedural. Whether the EPA responds with a substantive justification, commits to reviewing the evidence, or defers to a future monitoring cycle will determine whether microplastics move closer to regulated-contaminant status — the step that would trigger monitoring costs, treatment scrutiny, and new data obligations across the water and materials value chain.