EPA Declines To Require Microplastics Monitoring Under Its Proposed UCMR 6

On July 1, 2026, the U.S. Environmental Protection Agency (EPA) published its proposed Sixth Unregulated Contaminant Monitoring Rule (UCMR 6) that — despite years of pressure from states and advocacy groups — does not include microplastics. Under the Safe Drinking Water Act (SDWA), the UCMR is the mechanism EPA uses to require public water systems to monitor for unregulated contaminants and generate nationwide occurrence data that informs whether a contaminant should later be regulated. The proposed UCMR 6 would require monitoring for certain PFAS and other organofluorine compounds, several pesticide metabolites, and a range of semivolatile and purgeable organic compounds. Microplastics, which EPA included earlier this year on its draft Contaminant Candidate List 6 (CCL 6), were absent from the list — an issue EPA expressly addressed in the UCMR proposal.

In declining to include microplastics on the proposed UCMR 6, EPA pointed to the absence of a reliable way to monitor microplastics. Specifically, the agency explained that “there is no validated EPA or consensus drinking water analytical method with the proper quality control data, accuracy, and precision that could be used for UCMR 6, and it is not feasible to develop a drinking water analytical method within the statutory timeframe.” Without such a method, EPA reasoned, water systems would be unable to successfully monitor for microplastics, and requiring them to do so would sacrifice the opportunity to collect occurrence data on other contaminants for which validated methods already exist.

EPA also acknowledged in its UCMR 6 proposal that seven governors had submitted a November 2025 petition to include microplastics on the UCMR 6. The SDWA generally requires the agency to add a contaminant recommended by seven or more governors to the UCMR unless doing so would prevent the listing of contaminants of higher public health concern. EPA framed the proposed CCL 6 listing, rather than UCMR 6, as the appropriate first step toward understanding what public health risk microplastics may pose, stating the CCL listing would prioritize the research needed to develop analytical methods and support monitoring of microplastics in a future UCMR.

Because the UCMR is updated only about every five years, EPA’s decision — unless the agency changes course before the rule is finalized — likely forecloses nationwide federal microplastics monitoring until at least the next cycle. EPA is accepting public comments through August 31, 2026 and will hold public webinars on August 11 and 12, 2026.

For companies that manufacture, use, or otherwise place plastic-containing products into commerce, the lack of a current monitoring requirement for microplastics at the federal level is unlikely to slow the broader trajectory. State regulatory activity and private litigation focused on microplastics continue to expand, and the CCL 6 listing keeps microplastics on the federal research agenda. As new regulatory requirements and litigation risks take shape, companies should monitor these developments and consider discussing their implications with experienced regulatory and litigation counsel. 

© Arnold & Porter Kaye Scholer LLP 2026 All Rights Reserved. This Blog post is intended to be a general summary of the law and does not constitute legal advice. You should consult with counsel to determine applicable legal requirements in a specific fact situation.