Rainwater is no longer safe to drink anywhere on Earth by US contamination guidelines, according to a team of environmental scientists.

That's because rainwater across the planet now contains hazardous chemicals called per- and polyfluoroalkyl substances (PFAS). In a paper published in the journal Environmental Science & Technology on August 2, researchers at University of Stockholm, which has been studying PFAS for a decade, found evidence that these substances have spread throughout the entire atmosphere, leaving no place untouched.

There are thousands of PFAS, all human-made, used in food packaging, water-repellant clothing, furniture, carpets, nonstick coating on pots and pans, fire-extinguishing foams, electronics, and some shampoos and cosmetics. During manufacturing and daily use, they can be released into the air. They also leach into ocean water and get aerosolized in sea spray. From there, they spread through the atmosphere and fall back to Earth in rain.

They're often called "forever chemicals" because they linger for a long time without breaking down, allowing them to build up in people, animals, and environments.

PFAS have been found in Antarctica and in Arctic sea ice. Their prevalence across the planet is a hazard to human health, since peer-reviewed studies have linked them to some cancers, decreased fertility, reduced vaccine response, high cholesterol, and developmental delays in children.

Like microplastics, it is difficult to identify all the long-lasting health effects of PFAS exposure because they include so many different compounds and they are so prevalent in the environment. The new paper suggests that everybody on Earth is at risk.

Under EPA limits, 'rainwater everywhere would be judged unsafe to drink'

A woman and her granddaughter stand beside a rainwater tank used for washing and cleaning in San Miguel Xicalco, on the outskirts of Mexico City, Mexico, on March 4, 2016.Henry Romero/Reuters

Perhaps the most notorious among these substances are perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). In June, based on new evidence about health impacts, the Environmental Protection Agency significantly tightened its guidelines for how much PFOA and PFOS can safely be present in drinking water.

Previously, EPA had set the acceptable level for both substances at 70 parts per trillion. The new guidelines cut that by a factor of up to 17,000 — limiting safe levels to 0.004 parts per trillion for PFOA and 0.02 parts per trillion for PFOS.

The University of Stockholm researchers assessed the levels of PFOA, PFOS, and two other PFAS in rainwater and soil across the planet, and compared them to regulators' limits. Both substances' levels in rainwater "often greatly exceed" EPA limits, the study authors concluded.

"Based on the latest US guidelines for PFOA in drinking water, rainwater everywhere would be judged unsafe to drink," Ian Cousins, the lead author of the study and professor at the University of Stockholm Department of Environmental Science, said in a press release.

"Although in the industrial world we don't often drink rainwater [directly], many people around the world expect it to be safe to drink, and it supplies many of our drinking water sources," Cousins added.

The paper also found that soil across the globe was "ubiquitously contaminated" with PFAS. Because PFAS persist for so long and cycle through the planet's oceans, atmosphere, and soil so effectively, the researchers expect levels will continue to be dangerously high.

Ultimately, the researchers conclude that PFAS have exceeded the safe "planetary boundary" for human health.

"It is vitally important that PFAS uses and emissions are rapidly restricted," they wrote.