Scientists tested for 32 PFAS compounds — most of the ones detectable through available methods. Thousands of others are believed to exist but can’t be spotted with current technology, Smalling said.
The types found most often were PFBS, PFHxS and PFOA. Also making frequent appearances was PFOS, one of the most common nationwide.
Positive samples contained as many as nine varieties, although most were closer to two. The median concentration was around seven parts per trillion for all 32 PFAS types, although for PFOA and PFOS it was about four parts per trillion — the limit EPA has proposed for those two compounds.
The heaviest exposures were in cities and near potential sources of the compounds, particularly in the Eastern Seaboard; Great Lakes and Great Plains urban centers; and Central and Southern California. Many of the tests, mostly in rural areas, found no PFAS.
Based on the data, researchers estimated that at least one form of PFAS could be found in about 45% of tap water samples nationwide.
The study underscores that private well users should have their water tested for PFAS and consider installing filters, said Faber of the Environmental Working Group. Filters containing activated carbon or reverse osmosis membranes can remove the compounds.
The USGS study is “further evidence that PFAS is incredibly pervasive and folks who rely on private wells are particularly vulnerable to the harms caused by these chemicals,” Faber said.
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