In the 1970s, acid rain was one of the most serious environmental threats in North America and Europe. The air was so laden with pollution from coal power plants and cars at the time that it turned the rain toxic. Downpours killed fish, destroyed forests, eroded statues, and damaged buildings, sparking public outcry.
“Acid rain is a particularly alarming demonstration of the simple adage that what goes up must come down,” former Colorado Senator Gary Hart said in 1979. “With acid rain,” he said, “what comes down is much worse than what went up — worse in its potential damage to trees and crops, worse in its potential damage to fresh‐water lakes and fish and tourism.”
A few decades later, acid rain had largely disappeared.
Beginning around 1990, the US and Europe passed legislation that limited the amount of acid-forming pollutants — such as sulfur dioxide and nitrogen oxides — that power plants could emit. Laws requiring car manufacturers to put catalytic converters into new vehicles, which reduced harmful emissions, were also taking effect. That brings us to today: While precipitation in some regions is still unnaturally acidic, on the whole, acid rain is largely a problem of the past and a major environmental success story.
Now, however, there’s another problem with our rain — and it’s even more alarming.
While precipitation has become less acidic, a growing body of evidence suggests that it’s now full of many other pollutants that pose a risk to public health, including microplastics. And unlike the compounds that cause acid rain, these pollutants are almost impossible to get rid of.
The new pollutants in our rain
As government regulators focused on reigning in air pollution, companies were busy generating new sources of pollution, including plastics and PFAS, the so-called forever chemicals. PFAS, which stands for perfluoroalkyl and polyfluoroalkyl substances, are a large group of compounds used, among other things, to make fabric stain-resistant and pans nonstick.
Over time, these modern-era substances — which famously take decades to millennia to degrade — have leached into the environment, reaching every corner of the planet, no matter how tall or deep. Microplastics, PFAS, and some other compounds, such as pesticides, are now so widespread that they’ve essentially become part of our biome, not unlike bacteria or fungi.
They’re so common, in fact, that they’re even found in the rain.
A number of studies, for example, have documented microplastics in rain falling all over the world — even in remote, unpopulated regions. For one 2020 analysis in the journal Science, researchers documented microplastics in rainwater that fell on several national parks and wilderness areas in the Western US. Most of the plastic bits were microfibers, such as those shed from polyester sweaters or carpeting on the floor of a car. The researchers estimated that more than 1,000 metric tons of plastic from the atmosphere fall on parks in the West each year, including both as rainfall and as dry dust. That’s equivalent to roughly 120 to 300 million plastic water bottles, according to the study.
The largest source of those microplastics was highways, said Janice Brahney, a biogeochemist at Utah State University who led the Science study. Roads are often littered with plastic waste that gets broken down by cars and kicked up into the air. Those particles are typically lighter than soil, so once they become airborne, they can easily move around in the atmosphere and get grabbed by rain as it falls.
Another important source of plastic rain is the ocean, Brahney said. Several million tons of plastic enter the ocean each year, much of which breaks down into microplastics. When waves crash on the beach or bubbles burst on the sea surface, it sends microscopic plastic particles into the air.
Plastic rain is an environmental threat that’s harder to fix than the last one. “It’s much worse than the acid rain problem,” Brahney said. “With acid rain, we could stop emitting acid precursors and then acid rain would stop falling. But we can’t stop the microplastic cycle anymore. It’s there and it’s not going away.”
The story of PFAS is similarly bleak: Researchers have detected these chemicals in rain across the planet from the US and Sweden to China and even Antarctica, often at levels above drinking water guidelines. For a study published in 2024 — titled “It’s raining PFAS in South Florida” — researchers analyzed rainwater that fell around Miami and found more than 20 PFAS compounds, including PFOS and PFOA. Although these two PFAS were phased out in the US years ago due to public health concerns, the researchers still found them at concentrations beyond government health advisory levels for drinking water, underscoring the remarkable persistence of forever chemicals.
For another article, published in 2022, scientists reviewed studies of PFAS in rainwater and similarly found concentrations of these chemicals at levels above what US and Danish regulators say is safe for drinking water. The authors concluded that, based on health advisories, no untreated rainwater would be considered safe to drink.
“For us to get rid of PFAS, we probably have to go back in time,” said Natalia Soares Quinete, a chemist at Florida International University who was involved in the 2024 study. Even though the government is increasingly regulating PFAS, she said, “I don’t see us completely getting rid of those chemicals.”
The good news is that most people — especially in wealthy countries like the US — don’t rely on untreated rainwater. What is concerning is that rain ends up in groundwater, rivers, and reservoirs that feed into municipal water systems.
Treatment plants help a lot, typically removing upwards of 70 percent of microplastics in water, but some still pass through. A study published earlier this year, for example, found a small amount of microplastics in bottled water and tap water in France. Similarly, typical filtration plants for municipal water remove some but not all PFAS. Authors of a 2023 study by the US Geological Survey, a federal agency, estimate that at least 45 percent of the country’s tap water has at least one type of PFAS present.
Treatment facilities don’t have the technology to treat all of the microplastic compounds, let alone the technology to measure them, Brahney said. “There are tens of thousands of chemicals involved, and we only understand a fraction of them,” she said.
Whether or not you’re at risk from microplastics, PFAS, and other chemicals is all about exposure — how much of those substances you’re breathing in or consuming. There’s not much of them in a single glass of tap or a bottle of water. The problem is that there are many other pathways that these pollutants can take to enter your body, such as through food. And over time they add up.
How to protect yourself from polluted rain
Avoid drinking untreated rainwater and eating snow, no matter how pristine it looks!
If you can afford to filter your water, you should. Standard filters like reverse osmosis — which runs water through a semi-permeable membrane — typically remove a large portion of microplastics and PFAS.
Opt for tap over bottled water to avoid ingesting microplastics. Tap water is also way better for the planet.
A recent study found that the human brains contain as much as a typical plastic spoon’s worth of microplastic, by weight. Scientists still don’t understand what impact that might have on human health, but they suspect that microplastics could be linked to cancer, heart and kidney disease, and Alzheimer’s.
Meanwhile, nearly all Americans have a measurable amount of PFAS in their blood, according to US health officials, though concentrations of some of them — including PFOA and PFOS — are declining. On the whole, forever chemicals are associated with a range of ailments including increased cholesterol, decreases in birth weight, and kidney cancer.
All of these contaminants can also be harmful to wildlife, which unlike most of us, do rely on untreated water. One study, for example, linked exposure to PFAS to impaired immune systems in alligators. “If we have these contaminants in our rainwater they’re getting into our groundwater,” Brahney said. “They’re infiltrating our soils. Every organism is interacting with rainwater.”
Ultimately, what all of this research reveals is that the planet is dirty, even if the filth can be hard to see. These chemicals are in the rain because they’re abundant in the environment — and they’re in the environment because they’re in the rain. And while there’s ongoing research, we don’t yet fully understand how those pollutants impact our bodies and our ecosystems. We just know they’ll be around for a very, very long time.
“To be honest, I cry, because there’s no walking this back,” Brahney said of microplastic pollution. “These particles don’t break down at a time scale that would be relevant. So yeah, we’re not escaping that.”
#PFAS #microplastics #pesticides #pollutants #rain
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