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ORS favors 2005 WHO dioxin TEFs; summarizes PFAS-in-septic-system studies and risk-guidance status
Summary
The MassDEP Office of Research and Standards recommended use of the World Health Organization 2005 toxic equivalency factors (TEFs) for dioxin risk calculations, and summarized recent research linking PFAS to septic systems while updating the advisory committee on the status of the department's risk-characterization guidance.
Greg Braun of MassDEP’s Office of Research and Standards told the Wayside Cleanup Advisory Committee that the office recommends using the World Health Organization’s 2005 toxic equivalency factors (TEFs) for dioxin TEF calculations for now, and that the agency is tracking PFAS research on septic-system contributions to groundwater.
Dioxin TEFs: Braun said analysts investigated available TEF sets and analytical issues in laboratory reporting (EPA Method 8290A). "We basically came to the conclusion that the 2005 TEFs from the World Health Organization are the most appropriate TEFs to use at this time," he said, adding that WHO updates in 2022/2024 have not yet been broadly adopted by EPA or other agencies. ORS advised that if analytical reports list total homologs (4–7 chlorinated homologs), those homologs should be reported but not included in TEF calculations because the homologs lack sufficient toxicity data and do not appear to trigger the same toxic-receptor mechanisms.
PFAS and septic systems: Braun summarized recent studies and interim data that suggest septic systems can be a source of PFAS to groundwater, including work on Cape Cod, a statewide Wisconsin survey, a New York state community study, an Ohio septic-pump-out study and an ongoing New Hampshire community tank study. He noted recurring use of tracer compounds (acesulfame and other artificial sweeteners) and certain pharmaceuticals to indicate wastewater/septic-system contributions and said the literature shows PFAS precursors and consumer-product chemicals in septic waste streams.
Risk-characterization guidance progress: Braun reported that ORS has progressed on multiple chapters of the department's risk-characterization guidance (10 of 17 chapters complete or near-complete) but that Method 3 (risk-characterization review) remains a major internal-review bottleneck. He said ecological-risk chapters are nearing review and that the full guidance remains a work in progress, with internal review and comment resolution continuing.
Why it matters: The TEF decision affects how dioxin-like compounds are quantified for risk calculations; the septic-system PFAS research affects how the department locates diffuse wastewater sources; and the ongoing risk-characterization guidance will shape how MassDEP staff and licensees assess human-health and ecological risk under the MCP.
Ending: Braun asked stakeholders to submit substantive comments and signaled that ORS is open to targeted conversations with practitioners to resolve implementation questions as chapters reach formal review.
