03/12/2025

How Microplastics Could Be Affecting Our Food Supply

The Washington Post | Shannon Osaka | March 13, 2025

How Microplastics Could Be Affecting Our Food Supply

Microplastics are floating in the air around us, surging through rivers and streams, and burrowing deep into soils. And now, a new study suggests that all those tiny pieces of plastic are also disrupting the growth of plants.

A paper published in the Proceedings of the National Academy of Sciences on Monday found that the tiny plastic particles could be slashing photosynthesis rates globally. Microplastics, the scientists estimated, are responsible for a reduction in photosynthesis of 7 to 12 percent worldwide in plants and algae. That cut in photosynthesis, the researchers warned, could also impact large-scale crops that humans depend on, such as wheat, corn and rice.

“It certainly is very alarming — they’re saying microplastics are having this very dramatic effect on crops and productivity,” said Mary Beth Kirkham, an agronomy professor at Kansas State University who was not involved in the paper.

Scientists are still working to understand how microplastics — defined as pieces of plastic less than 5 millimeters in size, or around the size of a pencil eraser — are affecting ecosystems around the world. Researchers say, however, that the small shards may be making their way onto crops and agricultural land. Tiny pieces of plastic have been found in most food products, from burgers to seafood, and one study estimated that in Europe alone, 63,000 to 430,000 tons of plastics are likely to pollute agricultural land through sewage sludge used for fertilizer.

But there haven’t been many studies on how microplastics affect plants’ growth. In the new paper, scientists from Nanjing University in China and other researchers around the globe created a database of plant responses to microplastics from 157 studies. Those studies found “strong and consistent” decreases in total chlorophyll content and in chlorophyll-a, both markers of photosynthesis.

They then used modeling and machine learning to extrapolate those findings to crops around the world. The scientists estimated that microplastics cost the world about 60 million tons of rice, 76 million tons of wheat and 109 million tons of corn every year — or about 9.6 percent of global crop yields.

Still, the authors of the paper caution that the estimates are preliminary. “There is currently no cause for undue alarm,” Baoshan Xing, a professor of agriculture at the University of Massachusetts at Amherst, said in an email. The current research, he noted, is based largely on findings from laboratory experiments, not field studies.

Willie Peijnenburg, a professor of environmental toxicology at Leiden University in the Netherlands, says that most laboratory experiments use tiny spherical plastic particles but that, in the real world, those particles could come in many shapes and sizes. “In the real environment, plastics will weather,” he said. “That again has an effect on the toxicity of the particles.”

Crop yields have been on the rise for many years. Corn yields, for example, increased by 47 percent between 1981 and 2010; soybean yields have increased by about the same amount. If microplastics are interfering with the photosynthesis of major crops, that means those yields might have been even higher in a world without microplastics in the soil, water and air.

Kirkham said that although the findings are concerning, it is premature to estimate how much microplastics are affecting global crops. “Sometimes the experiments have been done with leaves and plant parts, and we haven’t measured the photosynthesis in a normal environmental situation,” she said. “We need to drill down on these experiments, just to see exactly how the experiments have been carried out.”

Variations in soils and between two types of photosynthesis — C3 and C4 — could also affect how plants respond to microplastics, Kirkham added.

Small-scale studies have found that plants change when exposed to the tiny shards of plastic. In one of Kirkham’s studies, she compared wheat plants exposed to cadmium — a toxic heavy metal — and those exposed to both cadmium and microplastics. The plants exposed to microplastics took up 1.5 times the cadmium as those without, indicating that the microplastics were probably absorbing the cadmium and carrying it into the wheat.

“Microplastics are what we call vectors in the soil — the cadmium associates with the microplastics,” she said.

Other research has shown that exposure to particularly tiny pieces of plastic, or “nanoplastics,” inhibited growth in a type of mustard plant. The plastics can affect how plants pull nutrients and water from the soil and how they absorb carbon dioxide from the atmosphere.

Xing said that although some studies show mixed results, the paper found a clear link. “We identified a constant trend across rigorously designed trials,” he said, adding that scientists need to do further investigation into how microplastics affect plants.

“People say all these microplastics are just organic materials — innocuous,” said Kirkham. “But we don’t know that.”