EPA Develops Category-Based Approach to Accelerate PFAS Data Collection and Research

Earlier this year, Congress tasked EPA chemists with developing a process to prioritize per- and polyfluoroalkyl substances (PFAS) for research based on exposure risks, toxicity, and existing data. Under the Toxic Substances Control Act (TSCA), reporting, record-keeping, testing, and restrictions apply to chemicals of concern, including PFAS.

To address these requirements, EPA researchers created a category-based framework, grouping 128 PFAS into categories for streamlined data collection. This method, building on an earlier approach used for the National PFAS Testing Strategy, allows related PFAS to be assessed together rather than individually, with a model for classifying new substances.

The project results support EPA’s efforts to gather data on PFAS use via reporting rules and to issue TSCA test orders to generate toxicity data on specific chemicals within this large, under-researched group.

PFAS:

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals, widely used since the 1940s, that persist in water, air, and soil worldwide. Due to their durability and extensive use, PFAS are commonly detected in the blood of humans and animals. These chemicals are prevalent in:

• Drinking Water and contaminated waste sites.
• Consumer Products such as non-stick cookware, stain-resistant fabrics, paints, and cosmetics.
• Food Packaging including microwave popcorn bags and grease-resistant wrappers.
• Industrial Settings such as chrome plating, electronics, and textile manufacturing.
• Firefighting Foam used at airports and training facilities.

The EPA's PFAS Strategic Roadmap has prioritized action since October 2021, allocating $10 billion under the Bipartisan Infrastructure Law to combat emerging contaminants such as PFAS.

While studies link certain PFAS to harmful health and environmental effects, the toxicity of most remains unexamined. Ongoing research is crucial to understanding and mitigating these "forever chemicals".

CHEMICAL CATEGORY-BASED APPROACH:

EPA researchers developed a detailed categorization approach for PFAS using the following steps:

1. Initial PFAS List: The researchers applied the PFAS definition from the Toxic Substances Control Act (TSCA) to the Distributed Structure-Searchable Toxicity (DSSTox) database, retrieving a list of 13,054 PFAS. They also included 2,484 predicted PFAS degradation products from the non-confidential TSCA inventory, expanding the list to 15,538 PFAS.
2. Category Assignment: Using OECD structure-based classifications, each PFAS was assigned to a primary category. The primary categories were further divided into secondary categories based on chain length thresholds (≥7 vs <7).
3. Subcategorization by Chemical Fingerprints: Secondary categories were subdivided using chemical fingerprints to balance structural categories and similarity within each category, as measured by the Jaccard index.
4. Identification of Representative PFAS: From the 128 terminal structural categories created, a subset of representative PFAS was selected for data collection. Factors such as the availability of toxicity data, environmental monitoring, and the potential to identify responsible manufacturers/importers guided this selection.
5. Future Refinements: The approach includes potential updates using mechanistic data and physicochemical properties, aiming to improve hazard assessments and QSAR development. This categorization method helps identify high-priority PFAS for further research and regulatory action.

This systematic approach helps to prioritize PFAS for further analysis and supports efforts in environmental monitoring and risk assessment.