Canadian Water and Wastewater Association eBulletin

EPA releases draft PFAS toxicity assessments

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The U.S. Environmental Protection Agency (EPA) announced draft toxicity assessments on Nov. 14 for GenX chemicals and perfluorobutane sulfonic acid (PFBS). GenX and PFBS are members of the broader per- and polyfluoroalkyl substances group.  

The draft assessments reflect available data suggesting:

  • GenX chemicals are carcinogenic.
  • While there is not sufficient evidence to state that PFBS is carcinogenic, it appears the thyroid and kidney are sensitive to PFBS.

EPA’s assessments include proposed reference dose values for subchronic and chronic exposures. Subchronic refers to repeated exposure for more than 30 days, up to approximately 10% of the lifespan in humans, while chronic reflects lifetime exposure.

The reference doses provided by EPA reflect an assessment of the hazard posed and dose-response relationship associated with GenX and PFBS but are not a complete characterization of the risk posed. The toxicity values proposed are higher than the RfDs EPA used to calculate the PFOS and PFOA drinking water health advisories.

The draft RfD for chronic GenX exposure is 0.00008 mg/kg-day; this compares to 0.0001 mg/kg-day used by North Carolina in setting its Drinking Water Provisional Health Goal at 140 ng/L. This RfD is also somewhat higher than those used to calculate the PFOA and PFOS drinking water health advisories (0.00002 mg/kg-day). The draft RfD for chronic exposure to PFBS is 0.01 mg/kg-day. Following publication in the Federal Register, there will be a 60-day comment period.