A Growing Concern: Microplastic Pollution on Farm Fields

Scientists are showing that we are sending tons of tiny plastic particles into our soils each year, potentially affecting crops and our health.

Farmworkers planting strawberry seedlings in rows of plastic mulch

Credit: VW Pics/Getty

Jenna Gavigan tries not to wash her clothes as often as she once did. Since embarking on her master’s thesis on plastic pollution four years ago at the University of California, Santa Barbara, Gavigan has also cut back on the amount of clothing she buys. Her research evolved into a study—published in PLOS ONE in September—documenting the growing amount of microfiber plastic pollution on land, the first such study since people began stitching synthetic fibers into clothes in the middle of the 20th century.

The paper, Gavigan says, “gives the whole, entire history of microfiber emissions from apparel.” Studies show that these synthetic threads account for a significant portion of the microplastic pollution problem. The five enormous gyres of plastic swirling in oceans across the world have received a lot of attention in recent years, but less is known about the problems that microplastics—those itsy-bitsy particles roughly 5 millimeters in diameter or smaller—are posing in the terrestrial environment.

A growing body of research shows that those teensy plastic particles end up not just in waterways but also on farmland, raising concerns over our food supply and our well-being. Contaminated crops could potentially be one of myriad ways that plastic—from its production to its use to its “disposal”—is harmful to our health, especially for people of color and low-income communities, where exposure rates tend to be higher at each phase of the plastic life cycle.

Gavigan and her coauthors estimate that between 1950 and 2016, the amount of synthetic microfibers entering the world’s oceans, rivers, lakes, and soils comes in at 5.6 million metric tons.

Cumulative microfiber emissions worldwide from 1950 to 2016

Gavigan J, Kefela T, Macadam-Somer I, Suh S, Geyer R (2020) Synthetic microfiber emissions to land rival those to waterbodies and are growing. PLoS ONE 15(9): e0237839. https://doi.org/10.1371/journal.pone.0237839

When people wash their synthetic threads, microfibers are released and flow into wastewater treatment plants. From there, up to 99 percent of the microfibers, Gavigan’s research finds, wind up in sludge that treatment plants offer to farmers who spread it on their fields as fertilizer. The researchers conclude that 92 percent of all microfiber emissions on land come from these biosolids.

But clothing isn’t the only culprit. In addition to synthetic fabrics, soil plastic can come from car tires that degrade on roadways, from cosmetics that wash into wastewater and concentrate in sludge, and from tools that farmers use on their land, such as plastic mulch, seed coatings, and coverings that keep out weeds and pests.

Scientists are still unclear about the impacts that microplastics might have on crops and the people who eat them. “We are, unfortunately, confirming that yes, agricultural soils are a hot spot of plastic contamination,” says Luca Nizzetto, a researcher with the Norwegian Institute for Water Research, who coauthored an op-ed about the issue in 2016 for Environmental Science and Technology. According to the op-ed, as much as 300,000 tons of microplastics end up on North American farmlands each year. “We don’t know exactly the environmental implication,” Nizzetto continues. “We are at the beginning of this story.” But recent studies offer some clues.

Sewage sludge being applied to a farm field in Geneva, Illinois
Credit: City of Geneva via Flickr

Kansas State University plant physiologist and agronomist Mary Beth Kirkham conducted a lab experiment in 2019 involving wheat plants, microplastic, and cadmium, one of the most toxic elements in sewage sludge. (Sludge also contains toxinslike PFAS, which are associated with serious health issues and can contaminate cows and dairy products when applied to farmland.) Ingesting cadmium at a high enough level can make you throw up, but eating or drinking smaller amounts over time can lead to kidney disease.

Kirkham was so surprised by the results from the soil testing lab, she asked if the numbers were correct. The shoots grown with microplastic had 1.5 times more cadmium than the plants grown without. The microplastics act as an accelerant, “and we just aren’t testing for it,” she says. “I think it’s a serious problem. We’re producing billions of tons of plastics each year.”

As for issues of plant health and food production rates, Kirkham also found that plastic-contaminated soils had drainage problems, with water pooling on the surface. “I knew it was due to the fact that the microplastics were preventing infiltration,” Kirkham says. Then the plants began to die, so she had to end the experiment after just 30 days.

Mary Beth Kirkham and student Reshma Antony in a laboratory at Kansas State University
Credit: Dan Donnert

In other experiments, conducted by chemist John Scott at the Illinois Sustainable Technology Center, microplastics were found to harbor bacteria and pharmaceuticals. “Think of them as little sponges, soaking up everything around them,” says Scott, who has been studying microplastic pollution for the last six years. And that’s in addition to the chemicals, like BPA, used to make them in the first place.

To see how microplastics may be getting into farmlands, Scott is working with the U.S. Geological Survey in Iowa to test soils, streams near farms, and biosolids provided by wastewater treatment plants. Though he doesn’t expect results for about a year, what he finds could help provide a baseline that toxicologists can use to develop models and guidelines for how much microplastic farmland should be allowed to contain. “We know they’re ubiquitous and persistent; the big question is, are there adverse effects,” he says.

Another thing we know is that the microplastic problem is not going away anytime soon. Plastic production and use are at an all-time high. By 2050 we’ll have created 26 billion metric tons of plastic waste, “and it’s got to go somewhere,” says Scott.

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