EPA science advisers flag PFAS, microplastics gaps in draft CCL 6

A draft review dated 28 September 2026 from the US Environmental Protection Agency's Science Advisory Board calls on the agency to justify how it selected 88 contaminants for possible federal drinking water regulation, singling out PFAS, microplastics, neonicotinoid insecticides and cyanobacteria as gaps in the current method.

The document reviews the draft sixth Contaminant Candidate List, which EPA announced on 2 April 2026 and published in the Federal Register on 6 April. It comprises 75 individual chemicals, four chemical groups and nine microbes — seven more entries than the final CCL 5's 81. The public comment period closed on 5 June. The full SAB was scheduled for a quality review at a public meeting on 19 October. The September version had not been approved by the chartered board and does not represent EPA policy.

The CCL is the first step in deciding whether a contaminant becomes regulated under the Safe Drinking Water Act. Listing imposes no obligations on utilities. EPA must, however, draw from the list to make regulatory determinations on at least five contaminants every five years.

What does the board want changed on PFAS?

The SAB reviewed the list and its three technical support documents at the request of EPA's Office of Water, through an augmented Drinking Water Committee that met between June and August. It acknowledges significant improvements over previous cycles but asks for more transparency on how contaminants were screened, selected and grouped.

The PFAS conflict is concrete. The draft CCL 6 retains the structural PFAS definition used for CCL 5, and the proposed group listing will exclude PFAS already subject to national drinking water regulations when the final list is published. The board states that trifluoroacetic acid, which it describes as the most abundant organofluorine compound in the environment, meets none of the definition's three structural criteria. Two other ultrashort-chain compounds, PFMOAA and PFPrA, also fall outside the definition — although EPA appears to treat them as PFAS elsewhere.

As a key revision, the SAB asks EPA to state whether excluding TFA is a deliberate policy choice. If not, the board says, the agency should list such compounds individually or revise the definition. Seven ultrashort-chain organofluorine compounds, including TFA, PFMOAA and PFPrA, appear on the proposed sixth Unregulated Contaminant Monitoring Rule, which EPA put forward on 1 July 2026 with 30 contaminants — the legal maximum per cycle.

Why do microplastics and insecticides raise questions?

EPA describes the microplastics listing, new to CCL 6 alongside pharmaceuticals, as a first step and admits data gaps including the absence of a health-based definition and a validated analytical method. The SAB argues microplastics are better understood as a source or vector of exposure than as a contaminant in the sense of the Safe Drinking Water Act. Chemical hazards may also arise from additives, monomers and degradation products that vary by plastic type and change as particles move through the environment and treatment plants. The board asks EPA to clarify whether tyre-wear additives such as 6PPD and its byproduct 6PPD-quinone fall under the group listing or require individual assessment. For future cycles, it suggests a separate evaluation process for microplastics and other groups that do not fit the standard chemical framework.

Only two neonicotinoids, clothianidin and thiamethoxam, made the draft list. The SAB wants an explanation for the absence of imidacloprid, which it calls the neonicotinoid used in the largest volumes worldwide and the one with the most extensive record of occurrence in drinking water. It suggests treating neonicotinoids as a group, as with PFAS and disinfection byproducts, given their shared mechanism of toxicity.

On DBPs, the board asks how EPA moved from eight high-scoring byproducts to a group of 27 unregulated DBPs, and why iodoacetic acids were left out. The report notes monoiodoacetic acid is more genotoxic than each of the regulated haloacetic acids.

What happened to cyanobacteria and microbes?

Cyanobacteria and their toxins appeared on CCL 1 and CCL 2; from CCL 3 onward only cyanotoxins were assessed. On 19 March 2026 EPA published final decisions not to regulate microcystins and cylindrospermopsin, concluding occurrence data did not show either toxin at levels of public health concern, though systems may struggle during severe blooms.

None of the nine microbes on the draft CCL 6 is a cyanobacterium. As a key revision, the SAB asks EPA to explain the exclusion and recommends including cyanobacteria in future cycles, citing how common harmful algal blooms are in US source waters. It also questions the shift toward confirmed waterborne disease outbreaks as the main microbe filter, which dropped Helicobacter pylori after every previous CCL, and recommends reconsidering Vermamoeba vermiformis, an amoeba linked to a Legionnaires' disease outbreak at a Minnesota community groundwater system.

For later cycles, the board wants the list to anticipate risks rather than rely on documented outbreaks, adding watershed factors such as agriculture and occurrence data from wastewater, stormwater and saline sources as utilities turn to reuse. It flags antimicrobial resistance genes and prions as contaminants fitting neither framework.

EPA says it will weigh public comments and the SAB's input before finalizing. CCL 5 was published on 14 November 2022; the statutory five-year cycle puts the final CCL 6 in November 2027.