“Forever chemicals”, more scientifically known as per- and polyfluoroalkyl substances (PFAS), are now so widespread that new research estimates it's unsafe to drink rainwater anywhere across the globe. Having spread globally in the atmosphere (now existing even in the air inside homes and schools), these human-made and harmful chemicals can be detected in rainwater and snow even in Earth’s most remote locations.

PFAS in rainwater were evaluated in a perspective article published in Environmental Science & Technology that looked at the concentrations of four PFAS in samples of rainwater, soil, and surface water from across the globe. The resulting concentrations revealed that the levels of PFAS greatly exceeded guidelines from the US Environmental Protection Agency Lifetime Drinking Water Health Advisory.

“Based on the latest U.S. guidelines for PFOA in drinking water, rainwater everywhere would be judged unsafe to drink,” said lead author Ian Cousins, a professor at the Department of Environmental Science, Stockholm University, in a statement.

“Although in the industrial world we don’t often drink rainwater, many people around the world expect it to be safe to drink and it supplies many of our drinking water sources.”

The regulation of PFAS in drinking water has decreased over the past two decades in light of new information regarding their toxicity. However, as the levels here have been relaxed it seems the environmental levels have increased, making what would’ve once been suitable drinking water out in the wild no longer safe to consume.

“There has been an astounding decline in guideline values for PFAS in drinking water in the last 20 years,” said Cousins. “For example, the drinking water guideline value for one well-known substance in the PFAS class, namely the cancer-causing perfluorooctanoic acid (PFOA), has declined by 37.5 million times in the U.S.”

PFAS get their nickname “forever chemicals” from their tendency to hang around. This has been demonstrated many times, but perhaps most notably by the presence of PFAS harmful to human health that have persisted in the atmosphere despite being phased out by a major manufacturer.

This is in part due to the foreverness of forever chemicals (though we are working on ways to get rid of PFAS), but also because there are processes in nature that will repeatedly recycle PFAS from the environment so that their levels remain consistent.

“The extreme persistence and continual global cycling of certain PFAS will lead to the continued exceedance of the above-mentioned guidelines,” said co-author Professor Martin Scheringer, who works from ETH Zurich in Switzerland and RECETOX, Masaryk University in the Czech Republic.

“So now, due to the global spread of PFAS, environmental media everywhere will exceed environmental quality guidelines designed to protect human health and we can do very little to reduce the PFAS contamination. In other words, it makes sense to define a planetary boundary specifically for PFAS and, as we conclude in the paper, this boundary has now been exceeded.”