The U.S. Environmental Protection Agency (EPA) is adding per- and polyfluoroalkyl substances (PFAS), microplastics, pharmaceuticals, and other hazards to the Sixth Contaminant Candidate List (CCL 6) for drinking water.

Stakeholders can submit comments on the draft CCL 6 for 60 days under docket number EPA-HQ-OW-2022-0946 at regulations.gov. EPA will also consult with its independent Science Advisory Board before finalizing the list, which is expected to be signed by November 17, 2026. 

What is the Contaminant Candidate List?

The drinking water CCL is a list of contaminants that are not currently subject to any proposed or promulgated national primary drinking water regulations, but are known or anticipated to occur in public water systems. EPA is required to publish an updated CCL every five years.

Contaminants listed on the CCL may require future regulation under the Safe Drinking Water Act (SDWA), but the CCL itself does not impose any requirements on public water systems. EPA uses the CCL to identify priority contaminants for regulatory decision-making and information collection.

New Contaminants Added to CCL 6

Announced on April 2, EPA is including four contaminant groups in CCL 6—microplastics, pharmaceuticals, PFAS, and disinfection byproducts—as well as an additional 75 chemicals and nine microbes that may be found in drinking water.

For the first time, EPA is designating both microplastics and pharmaceuticals as priority contaminant groups in the CCL.

Trump Admin EPA Withdrew Biden-Era PFAS Limits for Drinking Water

Prior to EPA’s unveiling of CCL 6, the Trump Administration's EPA rolled back legally enforceable maximum limits for PFAS in drinking water that were finalized under the Biden Administration in April 2024. These limits would have included PFOA, PFOS, PFNA, PFHxS, and HFPO-DA (also known as GenX Chemicals), which are known to exist in U.S. drinking water and have harmful health effects.

In May 2025, EPA rescinded the regulations for PFNA, PFHxS, GenX chemicals, and PFBS. EPA also extended the compliance deadline for PFOA and PFOS from 2029 to 2031.

Some estimates based on EPA contaminant testing data suggest that as many as 30 million Americans are served by water systems with PFAS concentrations exceeding limits for one of the four PFAS that EPA rescinded.

HHS Announces Initiative to Address Microplastics in Humans

On the same day as EPA's CCL 6 announcement, the U.S. Department of Health and Human Services (HHS) unveiled the Systematic Targeting Of MicroPlastics (STOMP) initiative under the Advanced Research Projects Agency for Health (ARPA-H), a nationwide $144 million program to create the definitive toolbox for measuring, researching, and affordably removing microplastics and nanoplastics (MNPs) in the human body.

Led by Ileana Hancu, Ph.D. and Shannon Greene, Ph.D., STOMP will focus on three technical areas across two phases: Measurement and Mechanism (Phase 1) and Removal (Phase 2).

1. Phase 1 will focus on understanding microplastics in the human body and developing measurement methods, including a clinical test that will quantify individual microplastic burden to support monitoring and interventions. This work will produce a risk stratification mechanism for plastic materials, ranking them by biological harm to help decision-makers identify and prioritize interventions.
2. Phase 2 will commence once Phase 1 illuminates which MNPs present the greatest risk to public health and how they affect human health. The goal is to develop methods to mitigate the harm caused by MNPs in the human body, once those harms are better understood.

Update, April 2, 2026: The article has been edited to include the STOMP announcement.