Bit by bit, microplastics from tires are polluting our waterways

Urban stormwater particles from tyre wear were the most prevalent microplastic a new Griffith-led study has found.

Published in Environmental Science & Technology, the study showed that in stormwater runoff during rain approximately 19 out of every 20 microplastics collected were tyre wear particles with anywhere from 2 to 59 particles per litre of water.

"Pollution of our waterways by microplastics is an emerging environmental concern due to their persistence and accumulation in aquatic organisms and ecosystems," said lead author Dr Shima Ziajahromi, a research fellow at the Australian Rivers Institute.

"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 tyre wear particles, is limited, as is the potential strategies we can use to minimise this source."

Tyre rubber contains up to 2500 chemicals with the contaminants that leach from tyres considered more toxic to bacteria and microalgae than other plastic polymers.

"Due to the analytical challenges in measuring this source of microplastics in stormwater, research to date often lacks information about the actual number of tyre wear particles water samples," said Dr Ziajahromi.

Quantitative information of this type is crucial to improve our understanding of the amount of tyre wear particles in stormwater, assess the risk to the environment, and to develop management strategies.

"Our study quantified and characterize microplastics and tyre wear particles in both stormwater runoff and sediment of stormwater drainage systems in Queensland," said co-author Professor Fred Leusch, who leads the Australian Rivers Institute's Toxicology Research Program.

"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.

"The device is a bag made of 0.2 millimetre 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," said Dr Ziajahromi.

"Urban stormwater runoff typically requires treatment for the removal of suspended solids and nutrients such as nitrogen and phosphorus in many jurisdictions in Australia, with some also requiring the removal of gross pollutants. However, regulations are lagging behind when it comes to microplastics and tyre wear particles."

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Florida's 76,000 stormwater ponds emit more carbon than they store

When you look at ponds, you might see birds and fish, but you probably don't think about carbon. In fact, Florida's 76,000 ponds store plenty of carbon, and a lot of it escapes into the atmosphere.

In fact, ponds lose more carbon via gas than they store in the muck, a new University of Florida study found.

"That finding means some ponds are doing us an ecosystem 'disservice,'" said Mary Lusk, a UF/IFAS assistant professor of soil and water sciences. "Globally, we expect that as urbanization continues, there will be more and more of these small human-made ponds in urban landscapes."

This research will inform scientists' attempts to estimate how much carbon is entering the atmosphere from these ponds on a regional basis, said Lusk, a faculty member at the UF/IFAS Gulf Coast Research and Education Center.

"Then, once people start to understand that better, we hope they will take stormwater ponds into account for policies related to carbon control," she said. "Stormwater ponds are everywhere in Florida. But they are understudied in terms of how they are impacting local ecosystems. Because they are human-made parts of the landscape, they sort of get overlooked, and people might assume they're not very important ecologically."

The sheer number of ponds compelled Lusk to study if they could have larger environmental effects than people think. She originally wanted to focus on nitrogen and phosphorus in ponds, but one of her graduate students, Audrey Goeckner, wanted to study carbon.

"When I learned that I had the chance to work in stormwater ponds, similar to what I had grown up in around in my neighborhood, I immediately asked myself, well what about these little urban ponds? How do they compare to other aquatic ecosystems?" asked Goeckner, now a Ph.D. student in soil and water sciences on the main UF/IFAS campus in Gainesville. "Turns out that despite their small size,

they can rapidly store and process carbon, which adds up when you consider how many of them exist in developed landscapes and how many continue to be built."

For the study, done as part of her master's thesis at GCREC, Goeckner designed a way to measure the amount of carbon leaving ponds. Although Goeckner studied ponds in Manatee County, her findings hold implications for pond carbon emissions globally.

Goeckner took two canoes (attached to each other) into the ponds. She and a lab technician each sat in one canoe to balance the weight. Goeckner then collected muck from the bottom of the ponds and measured the depth of muck above a sandy layer of sediment, indicating when the pond was constructed and the amount of organic carbon stored in it.

That's how Goeckner found the amount of carbon buried in the ponds.

Secondly, she modified a chamber that is normally used to measure greenhouse gases -- carbon dioxide and methane -- from soil. Instead, Goeckner used the chamber to measure these gases from the surface of the ponds.

She found the quantity of these gases that escapes from the ponds each year, and then compared carbon stored in the pond muck vs. carbon lost via gaseous loss. As a result, scientists now know that ponds give off more carbon than they store and that the amount lost changes over the lifetime of a pond.

As Florida continues to grow, it's going to become more urbanized. With new development often comes new stormwater ponds, which are not as good at storing carbon as older ones, Lusk said.

As ponds age, their sediment and biogeochemical properties may promote the amount of carbon stored, rather than emitted as a gas, Goeckner said. That translates to better storage efficiency of organic carbon that enters the water.

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