Déjà Vu in Drinking Water: Microplastics Regulation Follows the PFAS Playbook

[Artwork: Mandy Barker: Oceans. From Renoir to Microplastics. Museu Diocesa de Barcelona]

I've spent a lot of the past few years writing about per- and poly-fluoroalkyl substances (PFAS). Lately, I've noticed how familiar the microplastics story is; it’s like watching the same movie with different actors. f you want a preview of where microplastics regulation is headed, PFAS is basically the trailer.

Microplastics just made the federal watchlist for the first time

On April 6, 2026, the Environmental Protection Agency (EPA) published a draft of the Sixth Contaminant Candidate List (CCL6). For the first time in the list's 30-year history, microplastics showed up as a priority contaminant group alongside PFAS, pharmaceuticals, and disinfection byproducts. EPA Administrator Lee Zeldin announced it jointly with HHS Secretary Robert F. Kennedy Jr., which tells you this wasn't a quiet technical update - it was a coordinated federal signal. Public comment closed in June, and EPA aims to finalize the list by November 17, 2026.

That sounds like progress. It is progress. But watch what happened next.

EPA won't require anyone to actually monitor for microplastics

On July 1, 2026, EPA proposed the Sixth Unregulated Contaminant Monitoring Rule (UCMR6). This rule establishes the constituents that public water systems must monitor for. Microplastics were not on the list of the 2028–2030 sampling requirements.

What makes this notable isn't just the decision to not test for microplastics; it's how EPA got there. Seven governors formally petitioned in November 2025 to add microplastics onto the monitoring list. Under the Safe Drinking Water Act, EPA is generally required to honor a seven-governor petition, unless doing so would crowd out higher-priority contaminants. EPA sidestepped this by pointing to the lack of a validated test method, framing the CCL listing as the necessary first step before actual monitoring can take place.

The message is essentially this: EPA acknowledges that it's a priority, they just won't require the data that will tell us how big a problem it actually is. This is precisely the same sequencing that PFAS went through for years before enforceable limits arrived.

The science has been ahead of the policy for a while

The United States Geological Survey (USGS) has been quietly building a real dataset on microplastics, and some of it hits close to home for those of us in the Midwest. Back in 2016, USGS and the State University of New York at Fredonia (SUNY) collected and analyzed 107 water samples from 29 Great Lakes tributaries across Indiana, Michigan, Minnesota, New York, Ohio, and Wisconsin (including the Milwaukee River) and found microplastics in every single sample. The highest concentration of microplastics detected was 32 particles per cubic meter in the Huron River at Ann Arbor, Michigan.

Recently, USGS shifted the focus to agricultural streams. A statewide Iowa study in 2025 evaluated microplastics alongside PFAS, antibiotic-resistance genes (resistance markers), pharmaceuticals, and pesticides in small streams flowing through high-intensity agricultural watersheds. Every site that was tested detected measurable contamination, in addition to tissue-translocation risk (contaminants moving into fish or plant tissue, edible portions of contaminated fish carrying toxic loads to people, crops irrigated with contaminated watershed water getting into the food chain).

Microplastics aren't showing up in isolation — they're traveling in the same contaminant cocktail as everything else we've been tracking this year.

Groundwater has its own wrinkle, and it's a karst problem

This is the part I find most relevant to my own recent work. A 2022 study on karst groundwater systems found something that should catch the attention of anyone paying attention to development siting decisions in karst terrain: microplastics detected in groundwater correlate with direct hydraulic exchange with surface water through karst conduits more than with (slower) infiltration through soil.

In plain terms - in karst, groundwater can pick up surface contamination directly, avoiding the natural filtration in a typical granular aquifer.

States aren't waiting around

While federal rulemaking grinds through its multi-year process, states are moving forward on their own. This year, Colorado, Hawaii, Illinois, New Jersey, and Vermont introduced seven separate bills targeting microplastics in drinking water, surface waters, wastewater, personal care products, and even washing machines. It is expected that this trend will keep building, especially since federal actions are moving slower than the state-level appetites for it.

Why I'm watching this

The pattern here isn't subtle: such a broad detection of microplastics through studies conducted by USGS and academic researchers, followed by the CCL6 listing that acknowledges the risk, then the UCMR6 that neglects to list these contaminants, resulting in a gap that delays enforceable data collection, followed by states filling the vacuum on an individual state basis. The regulation of PFAS followed that exact sequence for the better part of a decade before associated maximum contaminant levels (MCLs) were established.

If microplastic regulation continues to stay on the same track as PFAS, the practical takeaway for anyone doing site characterization, expert witness, or local water policy work is this: don't wait for the federal monitoring requirement before you start asking the questions. The karst pathway alone is reason enough to treat microplastics as a significant consideration in any groundwater risk assessment, especially in areas involving fractured or carbonate geology - regardless of what EPA has or hasn't required (yet).

— Lori Huntoon, PG, Huntoon Environmental Risk Advisors