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.
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.
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.