PFOA and PFOS Regulation: Why These Two PFAS Face Different EPA Treatment

The EPA’s proposed PFAS drinking water rule keeps MCLs for PFOA and PFOS at 4 parts per trillion, while proposing to rescind standards for four other PFAS. This difference has created a key question for water utilities, chemical suppliers and procurement teams: why does the EPA treat PFOA and PFOS differently?

The answer sits in two areas. First, monitoring data shows broader occurrence and higher exceedance rates for PFOA and PFOS. Second, the EPA argues that the regulatory process for the other four PFAS did not follow the required Safe Drinking Water Act sequence.

PFOA and PFOS Remain the Core Regulatory Focus

PFOA and PFOS have long received the most attention in PFAS regulation because they appear more frequently in drinking water monitoring data. The EPA’s proposal maintains the existing MCLs for both substances at 4 parts per trillion.

This signals that the agency still sees PFOA and PFOS as the strongest candidates for national enforceable limits. For water systems, this means monitoring, treatment planning and compliance work for these two PFAS remain central.

Why the Other Four PFAS Face Proposed Rescission

The EPA proposes rescinding standards for four other PFAS because it identifies both evidentiary and procedural concerns. According to the EPA’s Federal Register notice and supporting Exponent analysis, UCMR 5 monitoring data showed that exceedances for PFHxS, PFNA and GenX occurred far less often than exceedances for PFOA and PFOS.

One key figure stands out. Only 64 water systems out of 9,238 monitored exceeded the PFHxS limit. The EPA uses this lower frequency to support a different regulatory treatment for these compounds.

The agency also argues that the rulemaking process for the four rescinded PFAS did not follow proper Safe Drinking Water Act sequential procedural requirements. This procedural issue forms a major part of the proposed rollback.

UCMR 5 Data and the Occurrence Gap

UCMR 5 monitoring plays a major role in the EPA’s reasoning. The data provides a broad view of how often different PFAS appear in public water systems.

The EPA’s position rests on a clear distinction:

• PFOA and PFOS show higher exceedance rates, which supports maintaining national MCLs.

• PFHxS, PFNA and GenX show much lower exceedance frequency, which supports reassessing their regulatory treatment.

• The lower occurrence rate raises questions about whether the same nationwide standard structure fits all six PFAS equally.

This does not mean the other PFAS lack concern. It means the EPA sees a weaker case for applying the same MCL framework without further procedural support.

The Safe Drinking Water Act Procedural Argument

The Safe Drinking Water Act requires a sequential process for setting drinking water standards. The EPA argues that the regulatory path used for the four other PFAS did not fully follow those required steps.

Independent analysis from sources including Jones Day has also focused on this procedural issue. The central argument is that drinking water regulation must follow the statute’s required order before enforceable limits become legally durable.

For procurement teams, this matters because procedural defects can create uncertainty. A standard that faces legal challenge may affect investment timing, project approval and long term treatment contracts.

What the Two-Tier PFAS Approach Means

The proposed approach creates a practical two-tier structure. PFOA and PFOS remain under enforceable MCLs, while four other PFAS move into a different regulatory position pending further action.

For water utilities, this may shape near term compliance priorities. Systems that detect PFOA or PFOS above 4 parts per trillion still need to plan for treatment, monitoring and reporting.

For suppliers, demand may stay strongest for technologies and chemicals used in PFAS removal from drinking water. Activated carbon, ion exchange and related treatment inputs may remain important where PFOA and PFOS drive compliance needs.

Why This Matters for Chemical Buyers

Chemical buyers should track this rulemaking closely because PFAS regulation affects purchasing decisions across water treatment, testing and environmental services.

Key procurement implications include:

• Treatment demand may focus first on PFOA and PFOS. Utilities may prioritize systems where these two compounds create direct compliance exposure.

• Testing programs may continue expanding. Water systems still need accurate detection to understand PFAS profiles.

• Regulatory uncertainty may delay some capital spending. Buyers may wait for final EPA action before committing to major projects involving the four other PFAS.

• State rules may still move independently. Some buyers may face stricter local requirements even if federal rules change.

The Bottom Line for Procurement Teams

The EPA’s proposed PFAS rule does not treat all PFAS the same because the agency points to different occurrence data and different procedural concerns. PFOA and PFOS remain regulated at 4 parts per trillion because the EPA sees stronger evidence and a clearer regulatory foundation for those limits.

The four other PFAS face proposed rescission because UCMR 5 data shows fewer exceedances and because the EPA argues the earlier rulemaking process did not follow proper Safe Drinking Water Act sequencing. For buyers, the key task now is to separate short term compliance needs from longer term regulatory uncertainty.

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