A Griffith-led study has found that constructed wetlands, built to treat wastewater and stormwater runoff, act as a barrier preventing the spread of microplastics through the environment.
Published in Environmental Pollution, the researchers investigated the amount and distribution of microplastics in water and sediment at five constructed wetlands with stormwater and wastewater sources feeding into the wetlands.
“Wastewater and stormwater are both critical pathways for microplastics to enter the aquatic environment,” said Mr Hsuan-Cheng Lu, a PhD candidate from the Australian Rivers Institute.
“Currently, there’s little information about the potential for constructed wetlands. They are a commonly used wastewater and stormwater treatment system to help diminish the flow of microplastics to the environment and their accumulation in the water and sediment of the wetlands.”
Constructed wetlands are proven filters for other chemical contaminants from stormwater. The researchers investigated how well they collect and retain microplastics.
The microplastic levels were up to four times higher in the storm/wastewater entering the wetland than water at the outlet. The microplastic levels in the constructed wetland sediment were higher than most reported freshwater sediment levels. The levels of microplastics are far more significant in the sediment at the wetland inlet than at the outlet.
“Wetland vegetation slows down runoff water, allowing microplastics to settle into the sediment,” said co-author Professor Frederic Leusch. He leads the ARI Toxicology Research Program (ARITOX) at the Australian Rivers Institute.
“These initial results showed the sediment carried a higher level of microplastics than most other freshwater environments globally.
“The wetlands act as a barrier preventing the microplastics from spreading further downstream, into our rivers and oceans.”
Wetlands can remove major forms of microplastics
The dominant form of microplastics was PET fibres, primarily from clothing and textiles. However, PE and PP were also found in the sediment from the breakdown of large plastic items.
As the study was carried out over the dry season in Queensland, more research is needed during wetter seasons and flood events. That will help determine if wetland barriers retain the plastics under the pressures of increased water flows or whether they get washed into ecosystems downstream.
“This study is an important first step. It shows that constructed wetlands can retain the microplastics in treated water and stormwater runoff. It also shows their sediment can act as sinks trapping and accumulating the microplastics over time,” said Mr Lu.
“The accumulation of microplastics and other pollutants in wetlands over time also raises concerns. Constructed wetlands provide critical habitats for wildlife in the urban landscape.
“For this reason, the logical next step after determining whether microplastic wetland traps survive the wet season’s rigours is to work with council engineers to investigate how the accumulated microplastics can be safely removed.”
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