Green roofs can capture nearly all the microplastic particles that contaminate rainwater in modern cities, according to a new study. The findings add to the list of benefits of green roofs, which have previously been shown to reduce energy needed for heating and cooling buildings and calm the flow of stormwater.

“These nature-based solutions can offer unexpected co-benefits in mitigating airborne pollution in densely built environments,” says study team member Shuiping Cheng, a researcher at Tongji University in Shanghai, China.

Microplastics—small bits of material formed from the breakdown of everyday plastic products—are ubiquitous. They’re found in soil, water, air, and even our bodies, and it’s increasingly clear that they pose risks to the environment, wildlife, and human health.

Most efforts to capture microplastics in urban environments have focused on filtering them out of surface runoff in bioremediation ponds, swales, and constructed wetlands. Since green roofs are known to filter heavy metals and excess nutrients from runoff, Cheng and his colleagues wondered if they could take care of microplastics as well.

The researchers created laboratory-scale mockups of green roofs composed of shallow plastic bins half a meter square and 85 millimeters deep. They added a filter to prevent the soil from washing away, a layer of drainage material, and soil, then planted the boxes with Rhodiola rosea or Sedum lineare, two species commonly used on Shanghai green roofs.

 

 

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The researchers then ground up plastic rubber into a powder of fine fragments, and pulled polyurethane into fibers. They added these microplastic particles to water at a similar concentration to what is found in urban rainwater.

They used a sprinkler-like apparatus to generate “rainfall” over the model green roofs, then measured the amount of microplastics found in the runoff, retained in the soil, and adhered to the plants.

The green roofs captured 97.5% of the microplastic particles that fell in a light “rainstorm,” the researchers report in the journal Communication Earth & Environment.

The city of Shanghai currently has 3.56 million square meters of green roof—a tiny fraction of all the roof space in the city. But even this modest array of green roofs could capture 56.2 metric tons of microplastic particles annually, the researchers calculated. This amounts to 1.65 times the amount of microplastics that enter the city’s urban water bodies from domestic wastewater.

“Our study highlights the powerful potential of urban green roofs to act as passive interceptors of atmospheric microplastics,” Cheng says.

In the study, most of the microplastics were captured by the soil rather than on the leaves of the plants. But this also depends on the particulars of the plants: Rhodiola rosea, which has leaves arranged in a rosette-like pattern, was better at capturing microplastics than Sedum lineare, with its thin, spiky leaves.

The green roofs also captured the irregularly-shaped microplastic fragments slightly better than they did the thin, slippery microplastic fibers. “We were surprised to observe that fiber-shaped microplastics captured by the green roof system could become resuspended into the atmosphere under airflow disturbance”—that is, windy conditions, Cheng adds. The findings highlight the difficulty of getting microplastic fibers such as those shed from modern stretch clothing out of the environment.

Green roofs are not likely to be a “set it and forget it” solution to microplastics. For one thing, the soil could become saturated with microplastics over time. Earthworms might be able to be deployed to break down and metabolize the microplastic fragments, the researchers suggest.

In addition, the filter and drainage layers of green roofs are sometimes made of plastic, which could become new sources of microplastic pollution themselves, the researchers warn. They buried pieces of polypropylene sheets in the soil of their model green roofs and observed signs of aging and degradation over the course of the experiment.

“A key next step is to validate these results under real-world conditions on full-scale green roofs,” Cheng says. “We are actively exploring opportunities to carry out such long-term field studies to better understand microplastic retention and release dynamics over time.”

Source: Huang J. et al. “Green roofs act as the first barrier to intercept microplastics from the urban atmosphere.” Communications Earth & Environment 2025.