Urban stormwater particles from tire wear were the most prevalent microplastic found, a new Griffith University (Australia)-led study said. Published by Scimex in Environmental Science & Technology, the study showed that in stormwater runoff during rain approximately 19 out of every 20 microplastics collected were tire wear particles with anywhere from two to 59 particles per liter of water.
“Pollution of our waterways by microplastics is an emerging environmental concern due to their persistence and accumulation in aquatic organisms and ecosystems,” lead author Dr Shima Ziajahromi, a research fellow at the Australian Rivers Institute, said. “Stormwater runoff which contains a mixture of sediment, chemical, organic and physical pollutants, is a critical pathway for microplastics to washed off from urban environments during rain and into local aquatic habitats. But to date, our knowledge of the amount of microplastics in urban stormwater, particularly tire wear particles, is limited, as is the potential strategies we can use to minimize this source.”
According to the report, tire rubber contains up to 2500 chemicals with the contaminants that leach from tires considered more toxic to bacteria and microalgae than other plastic polymers. Researchers say quantitative information of this type is crucial to improve our understanding of the amount of tire wear particles in stormwater, assess the risk to the environment, and to develop management strategies.
“We also assessed the effectiveness of a stormwater treatment device to capture and remove these contaminants from stormwater and evaluated the role of a constructed stormwater wetland for capturing microplastics in the sediment, removing it from stormwater runoff,” co-author Professor Fred Leusch explained. “The device is a bag made of 0.2-millimeter mesh which can be retrofitted to stormwater drains. Although originally designed to capture gross pollutants, sediment, litter and oil and grease, it significantly reduced microplastics from raw runoff, with up to 88% less microplastics in treated water which had passed through the device.”
Sediment samples collected from the inlet and outlet of a constructed stormwater wetland contained between 1450 to 4740 particles in every kilogram of sediment, with more microplastics in the sediment at the inlet than the outlet, indicating the wetland’s ability to remove them from stormwater.
“Microplastics that enter constructed wetlands for stormwater drainage systems settle in the sediment and form a biofilm, leading to their accumulation over time, removing them from stormwater runoff,” Dr Ziajahromi said. “Urban stormwater runoff typically requires treatment for the removal of suspended solids and nutrients such as nitrogen and phosphorus, with some also requiring the removal of gross pollutants. However, regulations are lagging behind when it comes to microplastics and tire wear particles.”
