Inclusion of Microplastics in U.S. EPA Draft Contaminant Candidate List

Author: Aidan Decker

Microplastics, which are coming under increased public scrutiny, were included in the U.S. Environmental Protection Agency’s (U.S. EPA) draft Sixth Contaminant Candidate List (CCL 6) on April 2, 2026. CCL 6 is a list of contaminants that are currently not subject to any National Primary Drinking Water Regulations (NPDWR) but have been known or anticipated to appear in public water systems (PWS) and may require future regulation under the Safe Drinking Water Act (SDWA). This marks the first time that microplastics will be included in this list of contaminants and continues a trend towards federal drinking water regulations being imposed on microplastics. The draft CCL 6 includes 75 chemicals, four chemical groups, and nine microbes that U.S. EPA has identified for potential regulation under the SDWA.

Microplastics are a broad grouping of small plastic particles with a diameter between one nanometer and five millimeters. Microplastics are formed through the breakdown of larger pieces of manufactured plastic and, due to their small size, are ingestible by humans. Microplastics have recently been linked to increased cancer risk, cardiovascular disease, and other adverse health effects, raising public concern and a drive to further research and regulate these particles. Microplastics have been observed in ground, surface, and desalinated tap water, which is why a potential drinking water standard has opened as a primary pathway to microplastics being federally regulated.

What is the Contaminant Candidate List or CCL?

U.S. EPA has been releasing drinking water CCLs since 1998, and the SDWA requires U.S. EPA to publish a CCL once every five years. The selection process for CCLs considers public input and consists of a three-step process:

• A broad list of contaminants is built for potential consideration, known as the CCL Chemical Universe;
• The CCL Chemical Universe is screened based on available health and occurrence information; and
• This information is evaluated in greater detail with the aid of U.S. EPA experts to finalize the CCL.

When CCL 6 is published on or before November 17, 2026, the included contaminants will not immediately be subject to any regulations. Instead, U.S. EPA will later separately determine whether the contaminants from the CCL should be regulated, which is referred to as a Regulatory Determination. The Regulatory Determination requires U.S. EPA to make a formal decision on whether to initiate a process to develop an NPDWR for at least five contaminants per CCL.

Future Regulatory Pathways for Microplastics

The addition of microplastics to the CCL 6 corresponds closely with a recent petition from seven U.S. governors to add microplastics to the Unregulated Contaminant Monitoring Rule 6 (UCMR 6). If microplastics are added to UCMR 6, they will undergo a testing period between 2027 and 2031, which will provide the data necessary to inform regulators on whether drinking water standards should be developed. Managers of PWS should pay close attention to whether they should expect to test their water for microplastics in the next few years.

Based on the attention being given to microplastics publicly and now by U.S. EPA, it is likely that NPDWRs will eventually be developed for microplastics. Standards may include Maximum Contaminant Level Goals (MCLGs) and Maximum Contaminant Levels (MCLs). MCLGs are the level of a contaminant below which there is no known or expected risk to health and are non-enforceable limits. MCLs are enforceable standards that set limits on drinking water concentrations of contaminants, factoring in best available treatment technology and cost.

Regulations imposed on per- and polyfluoroalkyl substances (PFAS) can offer insight on where microplastic regulations may be heading. The potential severity of health effects, ubiquity in drinking water, and public discourse surrounding microplastics aligns closely with PFAS. Several PFAS were included in UCMR 5 (2021) in CCL 4 (2016), and in CCL 5 (2021). U.S. EPA followed up in April 2024 by establishing MCLs for six PFAS in drinking water. While potential regulations for microplastics are still years away, it is probable that U.S. EPA will not stop its scrutinization of microplastics with CCL 6.

What Does This Mean for My Facility?

Should enforceable regulations be developed for microplastics, potential changes will be expected for owners of PWS along with many other facilities across the country. To meet MCLGs and MCLs, control technology with high capital and maintenance costs such as granular activated carbon filtration, ion exchange, or microfiltration may be required to be installed. Testing for microplastic removal technology has for the most part been conducted at the laboratory stage. It is expected that controls used to remove microplastics from water will evolve to become more scalable and cost-effective by the time their use is required. Monitoring requirements would also come with associated labor and financial burdens if deemed necessary to comply with NPDWRs. There is much uncertainty in how microplastic regulations will develop over the coming years, so it is important to stay up to date on how U.S. EPA proceeds following the publication of CCL 6.

Final Thoughts

ALL4 continues to track and keep our readers informed about important environmental regulatory updates. For questions related to the content in this article or about microplastics in drinking water, please reach out to Aidan Decker at adecker@all4inc.com or 571-554-8246. For any regulatory questions related to water or for strategical support on water-related issues, please refer to our Water Tech Team Lead, Lizzie Smith, at lsmith@all4inc.com or 770-999-0269.