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By Markham Heid

You’ve probably heard about the Great Pacific Garbage Patch. It’s the mass of plastic debris—now twice the size of Texas—that’s floating in the ocean between California and Hawaii. As if it that weren’t bad enough, four more large collections of plastic waste are spreading in the open waters of our blue planet.

While these minor continents of floating trash are the most startling indicators of global plastic contamination, they’re only part of the story—and maybe not the most concerning part. “I’m at least as worried about plastic pollution in terrestrial environments as I am about pollution in water bodies,” says Roland Geyer, PhD, a professor of industrial ecology at the University of California, Santa Barbara.

You can’t see them, but microscopic bits of plastic waste are gradually smothering our surfaces, suffusing our air, and saturating our ground soils. “Plastic doesn’t biodegrade like glass or paper into these more basic chemical elements, it just turns into smaller and smaller pieces of plastic,” Geyer explains.

A 2017 study in the journal Science Advances estimated that of the 8300 million tons of plastic that humans have thus far produced, we’ve managed to reuse or recycle just 9 percent of it. Another 12 percent has been incinerated, while 79 percent is still with us—in some form or another.

Geyer points out that the large-scale production and use of plastics only began in the 1950s, and the global ubiquity of cheap, disposable plastic packaging and goods is an even more recent phenomenon. “We’re just starting to look at how microplastics may adversely affect soil health or plant growth, for example,” he says.

We’re similarly ignorant when it comes to the consequences of microplastic contamination in our bodies—though it seems like that contamination is widespread.

For a study published in 2019, European researchers examined stool samples collected from eight healthy adults. All eight samples contained microplastics—mostly the type found in plastic water bottles and caps. Late last year, another study found microplastic particles in the placentas of four pregnant women.

Earlier this month, researchers at Health Canada—the Canadian government’s version of the U.S. Department of Health and Human Services—published a study framework intended to help researchers around the globe assess the threat of microplastic exposures on human health.

“There are three different ways that microplastics could cause toxicity,” says Sabina Halappanavar, PhD, first author of the study and a research scientist with Health Canada.

Plastic particles—depending on their size and shape—may penetrate tissues in ways that cause cell damage or an immune response, which are often the first steps in a progression that can lead to disease or dysfunction, Halappanavar explains. These particles could also carry chemicals that may be harmful to human health. Finally, they may serve as vectors for illness-causing pathogens, such as viruses.

She’s careful to say that, right now, we know very little about the average person’s microplastic exposures—let alone what these exposures may be doing to us. “What makes something toxic is often the amount or volume of exposure, and also the duration and frequency,” she says. These measures are likely to vary from person to person based on location and other factors.

Sorting out the effects of all this—on us, and on all other living things—is going to take a lot more time. But while hard-and-fast answers are in short supply, some experts have already highlighted microplastic exposures as a threat to human lung and respiratory health. Others have implicated microplastics as a potential driver of gut microbiome dysbiosis.

Dysbiosis refers to imbalances in the type, number, or interaction of bacteria in the human gastrointestinal tract. Researchers have linked such imbalances to diabetes, obesity, inflammatory bowel disease, colorectal cancer, and other medical conditions that were once relatively rare, but have been increasing progressively since the 1950s.

The drivers of these diseases are multifactorial. Western-style dietary patterns and the overconsumption of sugar have both been linked to gut dysbiosis and all its attendant health issues. But it’s possible that microplastic exposure—in our food supply, in our water, and in the air we breathe—may be contributing to the development of these and other medical conditions.

It would be nice if the problem of plastic contamination were getting better. Unfortunately, it’s getting worse. “Global plastic production and use is on a relentless growth curve,” says UCSB’s Geyer.

That’s true in countries with developing economies, he says. But it’s also true in the U.S., which has long been—and remains—the greatest contributor to the world’s burden of plastic waste. “It’s just this perfect storm of affluence ticking up, and plastic being so convenient and cheap that we can afford to use it and throw it away,” he says.

According to a report from the U.S. Environmental Protection Agency, Americans generated roughly 36 million tons of plastic waste in 2018—a nearly 13% increase from 2010. Much of this came from single-use packaging—food or beverage containers, for example, or household goods such as shampoos, liquid soaps, or cleaning products. Another major source is plastic toys and other cheap goods that, while technically not “single use,” are not built to last, Geyer says.

He acknowledges that we probably can’t live without plastic. “It is a phenomenally useful, convenient material,” he says. “But it comes with a big environmental price tag.”

Unless we can learn to live with less of it—much, much less of it—that price tag may soon be greater than our bodies and planet can afford to pay.

Markham Heid is a freelance health writer. His work has appeared in TIME magazine, The New York Times, and elsewhere. He’s a regular contributor at Elemental, a Medium publication, where an alternative version of this story first appeared.