Green roofs (rooftops covered with plants) are well-known for cooling cities, cutting energy costs and supporting urban wildlife. Now, researchers from Tongji University in Shanghai, China have discovered that green roofs could help reduce the amount of microplastics (tiny plastic particles less than 5mm) entering the environment through rainfall.

Microplastics are tiny fragments of plastic less than 5mm in size that are found in many of the everyday items we use. They are increasingly found in the environment and in our bodies.

Using a simulated rain system, the team tested different rooftop setups: bare roofs, plant-free green roofs, and roofs planted with common species like Rhodiola rosea and Sedum lineare. After several rounds of simulated rain, the planted green roofs were able to trap nearly all microplastics during light rainfall events as the soil beneath them were able to capture the particles efficiently.

The researchers found that the green roofs captured 97.5 per cent of the microplastic particles that fell in a “light” rainfall generator.

“These nature-based solutions can offer unexpected co-benefits in tackling airborne pollution,” said lead researcher Shuiping Cheng.

Currently, Shanghai has around 3.56 million square meters of green rooftops. Based on their findings, the researchers estimate that even this limited space could capture over 56 metric tons of microplastics from the air each year.

The researchers note that their findings are based on controlled experiments and real-world results may vary depending on factors like plant type, roof design and local climate.

Nevertheless, the study adds to growing evidence that green roofs can play a powerful role in creating cleaner, healthier cities around the world.

“We are actively exploring opportunities to carry out such long-term field studies to better understand microplastic retention and release dynamics over time,” added Cheng.

The study was published in the journal Communications Earth & Environment.

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