A study finds green roofs filter microplastics better than expected, catching 97.5% of particles during simulated rainfall.
Green roofs, already known for cooling buildings and controlling stormwater, may have a surprising new benefit: filtering out microplastics from rainwater. According to a recent study published in Communications Earth & Environment, green roofs can remove up to 97.5% of microplastic particles in urban rainwater.
Microplastics are tiny plastic fragments that come from broken-down plastic products, synthetic fabrics, and rubber. They’re found in the air, soil, and water—and even inside human bodies. These particles can pose health risks to people and wildlife. The study shows that green roofs filter microplastic particles effectively, offering a new tool in the fight against plastic pollution in cities.
Green roofs are layers of vegetation and soil installed on top of buildings. They are often used to reduce energy costs and manage stormwater. Now, scientists have discovered that green roofs filter microplastics.
Researchers at Tongji University in Shanghai, China, conducted the study. The team, including researcher Shuiping Cheng, built small-scale green roof models to simulate rainfall and measure the soil and plants’ ability to trap microplastics. They tested two types of plants commonly used in Shanghai: Rhodiola rosea, which has round, rosette-shaped leaves, and Sedum lineare, which has long, thin leaves.
To mimic city rain, the researchers sprayed water mixed with microplastics—rubber fragments and synthetic fibers—onto the green roof models. These were shallow plastic bins filled with soil, drainage layers, and filters to keep the soil in place.
After “raining” on the models, the researchers measured how much plastic ended up in the water runoff and how much was trapped by the soil and plants.
The results showed that 97.5% of microplastic particles were captured during light rain conditions. Most of the particles stayed in the soil, while some stuck to the plants. The plant Rhodiola rosea performed better than Sedum lineare at trapping microplastics, likely because its leaves offered more surface area.
Although green roofs currently make up only a small part of Shanghai’s roof space, they could still make a big impact. The researchers estimate that these existing green roofs could trap around 56.2 metric tons of microplastic each year. That’s 1.65 times more than the amount that enters the city’s water systems from household wastewater.
These findings suggest that expanding green roofs in cities could significantly reduce the amount of microplastic pollution reaching waterways.
The study also found that not all microplastics are equally easy to trap. The irregularly shaped fragments were captured more easily than long, slippery microplastic fibers. These fibers, like those that come from stretch fabrics, are harder to catch and can be blown back into the air by strong winds.
There are other challenges, too. Over time, the soil in green roofs could become overloaded with microplastics. The researchers suggest that earthworms could help break down and absorb the particles, but more studies are needed to test this.
Another concern is the materials used to build green roofs. The drainage and filter layers are often made from plastic, which could degrade and release more microplastics into the environment. In their experiment, the researchers buried plastic sheets in the soil and saw signs of wear and breakdown over time.
The study used small-scale models in a controlled lab setting. Researchers now want to test full-sized green roofs in real-world environments to see if they perform the same way. These field studies will help determine how long green roofs can continue to trap microplastics before they become saturated or start rereleasing them.
“We are actively exploring opportunities to carry out such long-term field studies to better understand microplastic retention and release dynamics over time,” Cheng said.
If you live in a city, green roofs could be part of the solution to microplastic pollution. While building a green roof may not be an option for everyone, supporting city initiatives that promote green infrastructure can make a difference. Green roofs filter microplastic, reduce flooding, improve air quality, and save energy—making them a smart investment for cleaner and healthier urban environments.
