A team of UCLA researchers has put a new spin on the 1970s rock classic “Dust in the Wind” — only this one is grittier and grimmer than Kansas’ original hit.
They found that wind picks up microplastics from human sewage-based fertilizers in higher concentrations than previously known, and may be an ‘underappreciated’ source of airborne plastic bits, flakes and threads.
“If you blow wind on a soil with microplastics, you would expect to see a similar amount of soil and microplastics in the dust,” says Sanjay Mohanty, a professor of civil and environmental engineering at UCLA. “But here we found less soil in the dust and much more microplastics. This means that every time the wind blows, the particles preferentially leave the soil.”
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That’s problematic, he said, because it means people may be breathing in these particles, which are between 1 and 5,000 micrometers, or 5 millimeters, in size. Most of these particles are likely coated with harmful chemicals such as plastic additives, heavy metals, pesticides and other chemicals that have flowed down drains or seeped from streets to storm drains.
It’s these “passenger” chemicals that pose the biggest health problem, Mohanty said, citing a growing body of research on known and potential harm.
“The more plastics we put out there, the more they will end up in the soil, in the water and in people’s food and bodies,” said Avi Kar, a senior attorney and director of the Natural Resources Defense Council’s Health and Food , People. & Communities program. “And they will bring with them the many harmful chemicals used to make plastic.”
In many major cities around the world, including Los Angeles, municipal sewage systems process human waste by separating wastewater from biowaste. The wastewater is filtered and often injected into the ground, where it is filtered again to be used for irrigation and in some cases drinking water. The biosolids – the residue left behind – can be dehydrated, repackaged and sold as fertilizer.
Globally, annual production of biosolids is estimated at 100 million tons, according to Mohanty and colleagues. This is expected to increase to 175 million tonnes per year by 2050. According to U.S. Environmental Protection Agency estimates, more than 2 million dry tons of biosolids are applied to land in the United States each year.
In 2011, 51% of the country’s biosolids were applied to land and agricultural fields; 22% was dumped in landfills; 16% were burned; and 11% were subjected to other management practices.
Sludge-based fertilizers are attractive for ecological and economic reasons. They offer farmers and gardeners a natural and sustainable way to reintroduce nutrients into the soil and extend the life of municipal landfills.
For example, Los Angeles County’s sanitary districts treat the sewage of 5.6 million people. In 2022, they produced approximately 110,000 tons of fertilizer, 20,000 of which was processed at the Tulare Lake Compost site, southeast of Kettleman City.
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In 2021, Mohanty and his colleagues discovered that sludge-based fertilizers contained many more plastic particles than previously suspected.
More recently, however, the team set out to find out what happened to the particles in the compost. To do this, they spread fertilizer on fields in Lind, Washington, about 75 miles southwest of Spokane. They then placed portable wind tunnels over the plots and turned on the fans. They discovered that microplastics are about 2.5 times more likely to end up in the air than other soil particles.
The reason for this, says Mohanty, is that microplastics are not ‘sticky’ like the other elements. He said California farmers and gardeners often use water on their fields and lawns during the summer months, not only to irrigate crops but also to reduce dust. Because plastic does not absorb water, it does not stick to the soil like minerals and organic material.
“The findings are not surprising given the ubiquitous nature of plastics in agriculture and the low densities and weights of microplastics,” said Mark Gold, director of the Natural Resources Defense Council’s Water Scarcity Solutions Program, who was not involved during the investigation. .
Shelly Walther, an environmental scientist with the Los Angeles County Sanitation Districts, said she was a little wary about how the researchers went about identifying and counting microplastics in their samples.
She said that while research into microplastics is growing, there are concerns in the scientific community about the methods and technologies used, as well as the reliability and reproducibility of some of the research.
But, she said, it is clear that there are microplastics in biowaste, and she is not surprised that some of them can become airborne. However, she wondered if all the plastic could be blown away. Some species are denser and less likely to be picked up by a breeze.
Nevertheless, she says plastic is a real and growing problem for the waste stream.
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LA’s sanitation districts have supported bills that would help reduce the amount of plastic that ends up in our waste at the source, including those that would require filters in washers and dryers.
Mohanty said washing machines are one of the biggest sources of microplastics in wastewater.
“Every time we wash our clothes, we produce millions and millions of fibers” that go straight into our wastewater, he said.
Bryan Langpap, spokesman for the sanitary districts, said “Hallelujah” when asked about laws designed to reduce plastic – and other contaminants – at the source.
“We just need to stop producing so much of this stuff. Because once it’s in our consumer products, and it’s in our homes, you can’t stop it from getting into the air and moving around,” he said, pointing research has found plastic particles in the Arctic, in the deepest trenches of the ocean, and in virtually every place scientists have looked.
He said the problem may be even bigger than we know, citing recent research that found hundreds of thousands of nanoplastic particles in single-use water bottles – an issue Mohanty has also considered when it comes to plastic in fertilizers.
He said that, unlike microplastics, his models show that nanoplastics – which range in size from 1 nanometer to 1 micrometer – are more likely to stick to soil, due to their stronger attraction to surfaces. And while that may keep them from getting into the air and into our lungs, it is possible that they are also absorbed by crops and plants.
This story originally appeared in the Los Angeles Times.