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Persistent Pollutants

EPA releases draft safe daily dose for Chemours’s GenX chemical

Number is four times as high as agency’s level for PFOA or PFOS

by Cheryl Hogue
November 15, 2018 | A version of this story appeared in Volume 96, Issue 46


A human hand holds a drinking glass under a running water faucet.
Credit: Shutterstock
Wells and a river that provide drinking water in southeastern North Carolina are tainted with fluoroethers.

The U.S. Environmental Protection Agency is proposing a safe daily level for people to ingest of Chemours’s GenX fluoroether surfactant and its acid. The draft number suggests drinking or eating these chemicals is safe at a level four times as high as recommended for the industrial substances perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), but that level is still extremely low.

Chemours makes and uses GenX, which it substitutes for PFOA as a polymerization aid, at a plant in Fayetteville, N.C. The chemical is the ammonium salt of hexafluoropropylene oxide dimer acid (HFPO-DA). HFPO-DA is found in the Cape Fear River downstream of the Chemours facility as well as in nearby groundwater, rain, and treated drinking water.

EPA issued on Nov. 14 the so-called draft chronic reference dose of 80 ng/kg of body weight per day for the two fluoroethers combined. A reference dose is a maximum acceptable human exposure level likely not to cause appreciable health risks during a lifetime. The agency’s numbers are based on laboratory animal studies showing adverse effects in the liver, kidney, blood, and immune system and in fetuses.

In contrast, EPA chronic reference doses for PFOA and PFOS, substances no longer used but still found widely in drinking water supplies, are 20 ng/kg per day each. The agency in 2016 used those numbers to set a health advisory level of 70 ppt for the chemicals individually or together in drinking water.

Based on those 2016 calculations, the draft dose level for the two fluoroethers translates to a drinking water concentration of about 300 ppt, says Laurel Schaider, a researcher at the Silent Spring Institute, which studies the links between chemical exposure and women’s health. Translating a dose level into a drinking water concentration requires making assumptions such as the amount of water people drink each day and whether they’re exposed to the chemical through other routes, and regulators could make different assumptions than Schaider, she notes.

In addition to hazard assessment for GenX, EPA also released a draft chronic reference dose for perfluorobutanesulfonic acid (PFBS), used as a substitute for PFOS. That draft number is 10,000 ng/kg per day, based on thyroid and kidney effects in laboratory animals. Using the assumptions from the agency’s PFOS calculations, this amount to about 37,000 ppt in drinking water, Schaider says. PFBS has been detected widely in drinking water, waste water, and food packaging, EPA says.

The agency is accepting public comments on its draft toxicity assessments through mid-January and will finalize them in the future.


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