EPA’s decision, paired with a newly unveiled research program from the Department of Health and Human Services, increases scrutiny on these emerging contaminants.

By Julia A. Hatcher, Tom Lee, Hunter J. Kendrick, and Casey Lynn Kirk

On April 2, 2026, the US Environmental Protection Agency (EPA) Administrator, Lee Zeldin, announced the draft Sixth Contaminant Candidate List (CCL 6) at a joint event1 with Department of Health and Human Services (HHS) Secretary Robert F. Kennedy Jr. This announcement focused on the draft CCL 6’s inclusion — for the first time — of microplastics and pharmaceuticals as priority contaminant groups for evaluation under the Safe Drinking Water Act (SDWA).

The announcement signals a new chapter of federal attention on exposure to these emerging contaminants through drinking water. EPA published a Federal Register notice on April 6 officially announcing availability of the draft CCL 6, and interested parties have until June 5, 2026, to submit public comments.2 Thereafter, in addition to consideration of public comments, EPA will consult with its independent Science Advisory Board before finalizing the list, which EPA expects to do by November 17, 2026. Meanwhile, at this same April 2 event, HHS announced the launch of STOMP: Systematic Targeting of MicroPlastics, a $144 million program to develop methods for measuring and studying the impacts of micro- and nano-plastics in, and for removal from, the human body.

The announcement of the draft CCL 6 and STOMP at this joint event indicates a high degree of coordination between EPA and HHS with respect to the addition of microplastics to the CCL. Moreover, the framing at the event of the decision as a core element of the Make America Healthy Again (MAHA) agenda,3 underscores the political salience of the issue of microplastics and pharmaceuticals in drinking water. 

The Safe Drinking Water Act and the Contaminant Candidate List

The SDWA directs EPA to publish the CCL — a roster of currently unregulated contaminants that are known or anticipated to occur in public water systems and that may require future regulation — and to update the list every five years. In making CCL selections, the SDWA directs EPA to focus on those contaminants in drinking water that “present the greatest public health concern”4 and to give particular consideration to the effects of contaminants on vulnerable subpopulations, including infants, children, pregnant women, and the elderly. The CCL is the first step in the SDWA regulatory framework and does not, in itself, impose any regulatory requirements on public water systems. Instead, the CCL functions as a prioritization and pipeline mechanism with several important downstream consequences:

  1. The CCL serves as a source of contaminants for the Unregulated Contaminants Monitoring Rule (UCMR), a rule that EPA must issue every five years with a list of no more than 30 unregulated contaminants that public water systems must monitor to fill data gaps on their occurrence in drinking water. EPA considers the CCL in selecting UCMR contaminants, but a CCL listing is not a prerequisite for inclusion in the UCMR; data generated from the UCMR can inform future CCL listings.
  2. Each contaminant on the CCL must be evaluated by EPA at some point to determine whether establishing a Maximum Contaminant Level (MCL) through a National Primary Drinking Water Regulation (NPDWR) would present a “meaningful opportunity”5 to reduce public health risk. The SDWA requires EPA to conduct this evaluation for at least five CCL contaminants every five years. In general, few CCL contaminants evaluated by EPA advance to such regulation, and instead, most CCL contaminants receive what is known as a “negative”6 determination (i.e., that it is not necessary to regulate via an NPDWR).
  3. For contaminants where the data do not yet support establishment of an MCL through an NPDWR (or a “negative” finding of no regulation), EPA may issue either a screening-level health benchmark or a health advisory. While both are non-enforceable, a health advisory is a more fulsome technical document that EPA often issues to provide guidance for a contaminant being targeted by EPA for likely future regulation via an NPDWR. Health benchmarks, on the other hand, assist states, tribes, and public water systems in screening to determine whether levels of a particular contaminant in a particular system may pose potential human health risks and are not necessarily a harbinger of such future regulation. 
  4. A CCL listing by EPA can catalyze coordinated and complementary research and data collection between EPA and other federal agencies. For example, contaminants identified as priorities by EPA may be incorporated into health surveillance efforts, such as the Centers for Disease Control and Prevention’s National Health and Nutrition Examination Survey (NHANES), which monitors the presence of chemicals in the human body across the US population. The announcement of the HHS STOMP program and the draft CCL 6 at a joint event indicates a high degree of coordination between EPA and HHS with respect to the addition of microplastics to the CCL. 

Proposed Addition of Microplastics and Pharmaceuticals to the CCL 6

The process for developing the CCL is a rigorous, multi-step process that includes consultation with the scientific community (including EPA’s Science Advisory Board), public notice and an opportunity for comment, and consideration of data in the National Contaminant Occurrence Database. For CCL 6, EPA solicited nominations from the public in a 2023 Federal Register notice. However, EPA received only limited public nominations in response to this notice, and as a result, appears to have drawn most of its new CCL additions based on other sources. EPA received one nomination for the inclusion of microplastics that was accompanied by three data sources, all indicating potential concern for exposure to microplastics, and three other comments from individuals supporting the addition of microplastics and pharmaceuticals to CCL 6.7

At the April 2 event announcing the draft CCL 6 and in the subsequent EPA CCL 6 News Release, EPA Administrator Lee Zeldin characterized the announcement as a core element of the Make America Healthy Again agenda,8 which has focused on issues related to toxic chemicals, food safety, and water quality.

Microplastics

In its April 6 Federal Register notice announcing the draft CCL 6’s availability, EPA identified the following questions as significant data gaps the agency believes exist for microplastics in drinking water:

  1. What “microplastics” are most associated with adverse health effects? EPA identified “the need to determine the characteristics of the microplastics (i.e., colors, polymers, shapes, sizes, etc.) most associated with adverse health effects in humans from exposure in drinking water.”9 Definitions at the state level developed to date have been cast broadly.10 Hence, any definition EPA approves that is more focused on materials that may actually present human health risks could serve as a template for states seeking to pursue their own regulations.
  2. How should entities test for microplastics? After answering the important definitional question above, EPA will need to develop a validated analytical method to reliably detect concentrations of those particular microplastics in drinking water that may be most associated with adverse health effects.
  3. What to do about microplastics in mixtures? EPA recognizes that microplastics often do not exist in isolation, and any evaluation of microplastics in drinking water will require an assessment of how microplastics occurring in mixtures may impact the detection of specific microplastics and the evaluation of their health impacts.
  4. Where do microplastics come from? After defining and better understanding the potential risks posed by microplastics in drinking water, EPA will need to determine their sources, in part to inform potential control strategies.

As EPA’s explanation for its draft CCL 6 listing makes clear, the inclusion of microplastics as a contaminant group will prompt more study and evaluation of how this family of materials should be defined in terms of human health risk potential and, if warranted, eventually regulated. Notably, the significant data gaps identified by EPA suggest a relatively long timeline until EPA would have sufficient data to evaluate whether to impose drinking water controls for particular microplastic compounds and sources.

Pharmaceuticals

As EPA noted in its April 6 Federal Register notice announcing the draft CCL 6’s availability, “[s]ince 2012, the EPA has led a Federal workgroup on pharmaceuticals in water alongside USDA, FDA, and USGS to exchange information on pharmaceuticals in the environment and to support the coordination of joint studies. The EPA committed to understanding contaminants in drinking water and has identified pharmaceuticals as an Agency priority.”11 EPA indicated that, as part of pursuing that priority, it will propose to include “a pharmaceuticals group on the draft CCL 6 to further prioritize research and information needed to identify which specific pharmaceuticals are occurring in drinking water and may be of greatest public health concern. For the purposes of the draft CCL 6, the EPA considers pharmaceuticals to include any substances defined as a ‘drug’ under the Federal Food, Drug, And Cosmetic Act (1938).”12

In the EPA CCL 6 News Release, EPA indicated that “antidepressants, hormones, antibiotics, and other drugs that enter water systems through human waste and improper disposal”13 will be a focus of the agency’s evaluation under CCL 6. EPA also emphasized that it is releasing human health benchmarks for 374 pharmaceuticals to give regulators a screening tool for evaluating potential risks when drug residues are detected.

PFAS, Microbes, and More

In addition to microplastics and pharmaceuticals, the draft CCL 6 includes two other contaminant groups — per- and poly-fluoroalkyl substances (PFAS) and disinfection byproducts — along with 75 individual chemicals and nine microbes. The inclusion of PFAS as a contaminant group in the draft CCL 6 continues the approach taken in the CCL 5. Notably, for this group, EPA defines PFAS based on the structural definition used in several of its Toxic Substances Control Act rules, which is a narrower definition than the one endorsed by the Organisation for Economic Co-operation and Development (OECD) and found in many U.S. state PFAS laws.

On the draft CCL 6, 38 of the 75 individual chemicals were also on the final CCL 5, meaning that nearly half of the chemicals on the draft CCL 6 would, if retained on the final CCL 6, be new to the program. These new-to-the-program chemicals include several agricultural pesticides (adding to the significant number of such pesticides being carried over from the final CCL 5); alloys and naturally occurring substances associated with the mining, metal, and energy industries; and compounds used in the production of rubbers, plastics, and acrylic fibers. The draft CCL 6 also would add nicotine to the program, which when present in drinking water from some sources would be encompassed by the pharmaceutical group listing (e.g., nicotine as a pharmaceutical ingredient in smoking cessation therapies), while from other sources would not be (e.g., nicotine from tobacco products).

Looking Ahead: What This Could Mean for Industry

Although CCL listing is an early step in a typically long regulatory process, the trajectory of PFAS as it relates to the CCL over the past two decades offers the most recent point of reference. Perfluorooctanoic acid (PFOA), one of the most well-known PFAS, was first placed on the CCL (CCL 3) in 2008.14 At the time, that listing was widely viewed as a preliminary, informational step. In the years that followed, however, PFOA’s presence on the CCL helped catalyze research and increasingly consequential regulatory and legal actions pertaining to PFOA in drinking water: inclusion in the UCMR monitoring program, issuance of health advisories, and ultimately finalization of an NPDWR with an enforceable MCL for PFOA in 2024. In the years since the CCL listing, companies that historically manufactured, processed, or used PFOA have faced significant private litigation, including related to impacts on drinking water. Although settlements worth billions of dollars have been reached with many public water systems, the potential exists for additional future litigation given the massive costs of compliance with the MCL. PFOA’s trajectory from CCL listing to the enforceable standard spanned roughly 16 years — but the business and legal consequences began accumulating well before the final NPDWR rule.

It is unclear whether this trajectory has any relevance at all to the newly added draft CCL 6 categories of microplastics or pharmaceuticals. As noted above, EPA’s study of pharmaceuticals in drinking water has been ongoing since 2012, and EPA’s issuance at the time of the draft CCL 6 of the screening-level health benchmarks for 374 pharmaceuticals indicates that the agency’s process is moving forward, but regulation, if any, of pharmaceuticals in drinking water may still be some years away.

As for microplastics, it is notable that public awareness and concern about microplastics have surged in recent years, driven by a steady stream of studies of varying types and degrees of quality indicating their presence in drinking water, food, and the human body. In November 2025, the governors of seven states also submitted a petition requesting that EPA include microplastics in the upcoming UCMR 6.15 Although it will likely be too soon for any particular microplastics to be identified and included in UCMR 6 given the need for additional study identified by the draft CCL 6 listing, the MAHA movement has currently amplified the political salience of the issue, as reflected by EPA and HHS holding an event to announce the draft CCL 6 release and STOMP. Hence, EPA and other agencies are expected to face pressure to continue to move forward in this area.

Moreover, some industry groups have publicly stated their support for a science-driven and coordinated response to microplastics. For example, the American Chemistry Council (ACC) issued a press release following the EPA and HHS event stating that “we support science-driven monitoring of microplastics in drinking water and research to better understand potential impacts. People want clear answers on microplastics, and any drinking water monitoring program must address several existing hurdles, including developing clear definitions, ensuring adequate lab capacity, and standardizing sampling and testing methods to be used consistently across the country.”16 ACC also continued to call on Congress to pass the Plastic Health Research Act in order to “establish a coordinated federal agency approach to microplastics research and support sound science-based policymaking.”17

The inclusion of pharmaceuticals and microplastics on the draft CCL 6 is a meaningful first step toward potential future EPA regulation of these compounds in drinking water, although as noted above, that regulation — if any — may still be some years away.

Latham & Watkins will continue to monitor and provide updates in this area.