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Persistent Pollutants

PFOA in rain worldwide exceeds EPA advisory level

Amounts of PFAS in precipitation called “practically irreversible”

by Cheryl Hogue
August 2, 2022 | A version of this story appeared in Volume 100, Issue 27

A hard rain falls on a wheat field next to a two-lane highway, with mountains in the background.
Credit: Shutterstock
Even in remote areas, precipitation contains levels of PFOA higher than the EPA recommends for drinking water, reserachers say.

Rain and snow around the world contain higher concentrations of a toxic, persistent industrial chemical than the US Environmental Protection Agency’s advisory level for the substance in drinking water, a new study says (Env. Sci. Technol. 2022, DOI: 10.1021/acs.est.2c02765).

Previous studies show that precipitation in urban, rural, and remote areas of Antarctica and Tibet had more than 0.004 part per trillion (ppt or ng/L), which is the EPA’s lifetime exposure health advisory level for perfluorooctanoic acid (PFOA).

The EPA introduced the PFOA advisory level, which isn’t a regulatory limit that US drinking water suppliers must meet, in June. The EPA sets such levels as recommendations for when water utilities should notify customers of contaminants. To set the level for PFOA, the agency relied on data linking exposure to this substance to suppression of people’s immune responses to vaccines, cardiovascular harm, and interference with the development of fetuses and babies. The EPA plans to issue mandatory limits, which the Safe Drinking Water Act requires to take into account analytical and economic factors, for PFOA and five other per- and polyfluoroalkyl substances (PFAS) later this year.

“Based on the latest US guidelines for PFOA in drinking water, rainwater everywhere would be judged unsafe to drink,” says Ian Cousins, an environmental organic chemistry professor at Stockholm University, who led the research.

The American Chemistry Council is taking the EPA to court over the advisory levels for PFOA and a related compound, perfluorooctanesulfonic acid (PFOS), in drinking water. The industry organization, which includes companies that may be liable for cleanup of the chemicals, claims the agency did not use the best available peer-reviewed data to establish those levels. PFOS poses health hazards similar to PFOA’s, according to the EPA.

Meanwhile, 3M, formerly the major US manufacturer of PFOA and sole maker of PFOS, phased out production of the molecules two decades ago, Cousins and his colleagues note. These two chemicals and several other PFAS are known to be cycling between surface water—notably oceans—and the atmosphere.

Such cycling means that levels of PFAS in rainwater “will be practically irreversible,” the paper concludes.

PFOA and PFOS have been included in foams used to extinguish liquid fuel fires. PFOA was also a processing aid for making fluoropolymers. PFOS was used in water- and stain-proofing applied to leather and fabrics.

Precipitation across most of the world, with the exception of Antarctica and Tibet, exceeded the EPA’s health advisory level of 0.02 ppt for PFOS, the study says. Similarly, the researchers found that precipitation in much of the world exceeded the Danish drinking water limit of 2 ppt for a combination of four PFAS—perfluorononanoic acid, perfluorohexane sulfonic acid, PFOA, and PFOS.



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