EPA’s draft Sixth Contaminant Candidate List prioritizes microplastics and pharmaceuticals in drinking water

On April 2, 2026, the United States Environmental Protection Agency (EPA) issued a pre-publication notice of its draft Sixth Contaminant Candidate List (CCL 6) under the Safe Drinking Water Act (SDWA). On April 6, EPA published the draft CCL 6 in the Federal Register and opened a public comment period through June 5, 2026.

The draft CCL 6 reflects a shift in EPA’s drinking water priorities. For the first time in the program’s history, the Agency has designated both microplastics and pharmaceuticals as priority contaminant groups for evaluation, alongside other key chemicals and microbes. EPA announced the draft CCL 6 list together with the US Department of Health and Human Services (HHS) and presented it as part of the Trump Administration’s Make America Healthy Again initiative.

While a chemical’s listing on the draft CCL 6 does not, in itself, impose limits or obligations, it signals where EPA intends to focus research, data collection, and inter-agency coordination, shaping drinking water policy, monitoring programs, and enforcement risk over the coming decade.

This alert summarizes the key elements of draft CCL 6, explains the CCL’s role within the SDWA regulatory framework, and highlights considerations for stakeholders likely to be affected by EPA’s evolving priorities.

How the CCL works under the SDWA

Under the SDWA, every five years, EPA must publish a list of unregulated contaminants found, or expected to be found, in public water systems that may warrant regulation.

For listed chemicals, EPA evaluates:

• Potential adverse health effects
• Known or anticipated occurrence in public water systems at levels and frequencies of concern
• Whether the regulation of that chemical would provide a meaningful opportunity for risk reduction

EPA may also use an Unregulated Contaminant Monitoring Rule (UCMR) to gather nationally representative occurrence data.

Listing a substance in a CCL is the first step in regulating it in drinking water, but the path from CCL listing to enforceable standards is often long and uncertain. For example, the limited per- and polyfluoroalkyl substances (PFAS) standards finalized in 2024 followed multiple CCL and UCMR cycles and reflected an atypical convergence of scientific development, litigation pressure, and policy prioritization. The EPA has announced its intent to rescind maximum contaminant levels (MCLs) for certain PFAS, including: 1) Perfluorohexanesulfonic acid (PFHxS), 2) Perfluorononanoic acid (PFNA), and 3) Hexafluoropropylene oxide dimer acid (HFPO-DA GenX)

The EPA would retain the standards for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) but extend the compliance deadline until 2031.

In March 2026, EPA declined to regulate any of the nine contaminants evaluated from the fifth CCL. In practice, while the CCL signals agency interest, EPA’s regulatory determinations are driven by analytical feasibility, treatment availability, cost considerations, and litigation durability – not CCL listing alone. The draft CCL 6 may be understood as guiding research and prioritization rather than predicting possible regulatory changes.

Key elements of draft CCL 6

The draft CCL 6 emphasizes both contaminant groups and individual contaminants. It includes four contaminant groups:

• Microplastics
• Pharmaceuticals
• PFAS
• Disinfection byproducts

It also includes 75 individual chemicals and nine microbes. EPA’s use of contaminant group listings allows it to advance research without committing to specific chemical definitions, analytical methods, or regulatory endpoints. The inclusion of pharmaceuticals reflects a decade of public attention, inter-agency work, and EPA’s completion of non-enforceable human health benchmarks to inform screening and prioritization.

While other federal laws (e.g., the Toxic Substances Control Act of 1976) have focused on reorienting regulation of PFAS to a risk-based, chemical-specific initiative, EPA has reaffirmed a group-based approach to evaluating PFAS via the draft CCL 6, citing the impracticability of evaluating PFAS individually in this context where “data are scarce for the majority of the PFAS.”

The draft CCL 6 also lists various plastic-related additives and industrial chemicals, including:

• Nonylphenol, 4-tert-octylphenol, bisphenol A, benzyl butyl phthalate, triphenyl phosphate, and tris(2-chloroethyl) phosphate
• Numerous pesticides
• Industrial solvents and intermediates
• Several metals and inorganic substances, such as manganese, cobalt, tungsten, lithium, iodide, strontium, vanadium, silver, and zinc
• Eight microbial contaminants, including three protozoa, five bacteria, and one virus

EPA identifies significant data gaps that must be addressed to support future regulatory decisions, including:

• A lack of a health-based definition tying microplastic characteristics to risk
• The need for validated analytical methods
• The challenge of assessing microplastics within complex environmental mixtures

The absence of validated, nationally deployable analytical methods has historically constrained EPA’s ability to advance contaminants for mandatory monitoring under the UCMR or to defend regulatory determinations in litigation. Method development and laboratory capacity may be limiting factors for future federal action on microplastics.

Publication of the draft CCL 6 in the Federal Register opened a 60-day public comment period. Comments may be submitted on or before June 5, 2026 to docket number EPA-HQ-OW-2022-0946 at regulations.gov. The EPA will also consult with the independent scientists of the Science Advisory Board before finalizing the list, which is expected to be signed by November 17, 2026.

Stakeholder considerations: Affected sectors and UCMR monitoring

Entities likely to be affected include:

• Polymer and chemical manufacturers that produce or formulate plasticizers, flame retardants, surfactants, and related additives
• Pesticide and agricultural chemical manufacturers with listed active ingredients
• Pharmaceutical manufacturers and supply chain participants
• Public water systems, particularly small systems, which often face disproportionate monitoring and treatment burdens as UCMR monitoring expands across successive cycles

Manufacturers and upstream actors may face heightened scrutiny before enforceable standards are proposed, as occurrence data, health benchmarks, and state-level initiatives develop in parallel. Public water systems, by contrast, often experience the most acute operational impacts once UCMR monitoring requirements expand, even in the absence of federal MCLs.

Implications for pharmaceuticals

The draft CCL 6 has several practical implications for pharmaceutical compounds. EPA now recognizes pharmaceuticals – including antidepressants, hormones, antibiotics, and other drugs – as a priority drinking water contaminant group, noting that these substances may enter water systems through human waste and improper disposal. EPA is also releasing human health benchmarks for 374 pharmaceuticals, providing states, Tribes, and local water systems a reference tool to assess risk. While non-binding, these pharmaceutical benchmarks could influence state and local regulatory decision-making and risk-assessment practices.

EPA now also recognizes microplastics – tiny plastic particles reported to be in human blood, breast milk, and organs – as a drinking water priority. Research into the health effects of microplastic exposure is in its initial stages, and scientists are assessing the extent of the threat to human health. Concurrently, HHS unveiled its Systematic Targeting of MicroPlastics (STOMP) initiative, a USD144 million program under the Advanced Research Projects Agency for Health to develop tools for measuring, researching, and potentially removing microplastics from the human body.

Chemical and plastics manufacturers are encouraged to review the CCL listing and the STOMP initiative, which may signal increased federal focus on microplastics as a public health concern. Pharmaceutical companies may note that the publication of human health benchmarks for 374 compounds, coupled with the prioritization of pharmaceuticals in the CCL, could increase scrutiny of pharmaceutical residues in waterways and drinking water.

Microplastics and the UCMR: Monitoring, methods, and potential data gaps

In late 2025, several governors petitioned EPA to include microplastics in the upcoming UCMR 6 cycle. The EPA transmitted its proposed UCMR 6 to the White House for inter-agency review, although it remains unclear whether microplastics will be included. If they are, certain public water systems would be required to monitor for microplastics using EPA-specified methods, generating national occurrence data that could inform subsequent CCLs and regulatory decisions.

EPA acknowledged that developing and validating testing methods is key to including microplastics in the UCMR. Method readiness and the SDWA’s statutory maximum of 30 UCMR contaminants may influence whether and how microplastics appear in UCMR 6.

The multi-state petition is particularly significant because the SDWA requires EPA to give additional consideration to such requests. Although inclusion is not guaranteed, the petition pushes EPA to assess method readiness and to consider including microplastics in a national monitoring cycle before establishing health-based regulatory thresholds.

Looking ahead

The draft CCL 6 is an early-stage action in a typically lengthy regulatory process. The path from listing to enforceable drinking water standards could take years and face legal challenges.

Key uncertainties remain. For microplastics, the lack of a validated, nationwide analytical method suitable for UCMR is a threshold issue. For pharmaceuticals, EPA’s group listing signals priority but does not identify specific drugs or ingredients for action. UCMR 6 content is not yet public, and it is still unknown whether microplastics will be included, in what form, and with what methods.

The practical impact of the draft CCL 6 may depend on the availability of funding for research and monitoring infrastructure, the implementation of enforceable regulations, and the consistency of these efforts over time.

Next steps

Potentially affected companies are encouraged to review the draft CCL 6 lists and technical support documents against their product portfolios, operations, and supply chains to identify connections to listed contaminants or groups. Where connections are identified, companies may wish to consider submitting comments no later than June 5, 2026 to inform EPA’s understanding of occurrence, exposure pathways, method feasibility, treatment practicability, and cost implications.

Entities involved in microplastics measurement, product stewardship, or treatment technologies may be positioned to contribute to the development of analytical methods and the resolution of data gaps EPA has identified, which could help shape whether and how microplastics are incorporated into UCMR 6.

Learn more

DLA Piper’s Environment, Health, and Safety team routinely advises businesses on regulatory and policy developments affecting plastic and pharmaceutical companies, as well as across industries.

For questions or more information about draft CCL 6, please contact the authors.