Green Rooftops Could Help Cities Like Shanghai Filter Out Tons of Microplastics from Rainwater

The research team at Tongji University collaborated with a colleague from the Shanghai Academy of Landscape Architecture Science and Planning, finding that growing plants on roofs can be an effective method for removing microplastics from the air. In this study, published in the journal Communications Earth & Environment, the team measured the amounts of microplastics on the plants and soil in which they grow. Previous research has shown that growing plants on roofs can reduce heating and cooling bills, as well as clear the air surrounding them of pollution.

Testing Plant Types and Microplastic Exposure

As per the study, the research team found whether the growing plants have microplastics or not. To know this, they planted two different types of plants, which are used on rooftops in Shanghai. Further, they introduced microplastic particles in the air near those plants at common levels found in Shanghai. The researchers then introduced simulated rains, after measuring the microplastic levels in the soil and on the plants.

Green Roofs Trap the Majority of Microplastics from Rain

What they found was that the plants did a great job of pulling the microplastics from the rain by growing through the air above them. The green roof system created by researchers consisted of a soil layer, which pulled the microplastics from the rainwater that falls on it to around 97.5%.

Microplastics Mostly Captured in Soil, Not on Leaves

And after conducting the measurements through multiple rains, the team came to know that the percentage of microplastics removed further increased with the intensity of the rainfall.

The researchers found that leaves were collecting less of the microplastics, but the bulk was deposited in the soil in a better way, rather than in a fibre-like shape.

Shanghai's Green Roof Potential to Capture Microplastics

The team noted that Shanghai currently has only 38.33 million square feet of roof occupied by vegetation. However, based on their findings, they suggest, it is possible that Shanghai could capture around 56.2 metric tons of microplastic every year if the rooftops of all the buildings were made green.