Why a ‘safe’ PFAS level in drinking water is so ambiguous

If Hemlock’s home were in New Jersey instead of Michigan, her contamination level wouldn’t just be considered unsafe, it would be four times above a proposed legal limit of 14 ppt for PFOA in drinking water there.
The testing has prompted tough questions about what level of PFAS is safe to drink, with state agencies offering sometimes confusing guidance about the toxicity of contaminants considered "possible" or "probable" carcinogens, but which are still being studied.
The EPA’s interim advisory level was 400 ppt — about five times the eventual lifetime health advisory set at 70 ppt in 2016.
In Belmont, Wolverine initially only offered whole house water filtration systems to homes testing above 70 ppt before agreeing to provide them to any home with any level of PFAS in a testing area southeast of the company’s House Street landfill.
Clapp, a retired environmental health professor at Boston University School of Public Health and adjunct professor at the University of Massachusetts Lowell, has studied the health effects of PFAS and co-authored research with Harvard professor Philippe Grandjean, whose estimate of 1 ppt as the safe PFAS level in drinking water is embraced by public health advocates unhappy with the EPA threshold.
Minnesota — home to 3M, which manufactured the chemicals Wolverine used at the tannery — updated its standards in May to 35 ppt for PFOA and 27 ppt for PFOS.
Is 2 ppt safe?
Is 15 ppt safe?
In Michigan, for now, DHHS says 70 ppt is the "safe" level.
"We’re going with 70 ppt because it’s a well-calculated number," said Groetsch.

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