University of Michigan researchers have uncovered new information about an emerging technique that could be used to track microplastics from space. It turns out that satellites are the best at detecting soapy or oily residue, and microplastics seem to bond with those residues.
Microplastics — tiny particles that can ride ocean currents hundreds or thousands of miles from their point of entry — can harm marine life and marine ecosystems, and they are extremely difficult to track and clean up. However, a 2021 discovery raised hope that satellites could provide daily schedules for prevention and cleanup efforts on where microplastics enter the water, how they move and where they accumulate.
The team found that data recorded by the Cyclone Global Navigation Satellite System (CYGNSS) showed lower surface roughness – meaning fewer and smaller waves – in areas of the ocean containing microplastics compared to clean areas.
In preliminary tests, they used the technique to detect suspected releases of microplastics at the mouth of China’s Yangtze River and to identify seasonal variations in the Great Pacific Garbage Patch, a convergence zone in the North Pacific where microplastics accumulate in large quantities. So far, however, the team hasn’t been sure about the nature of the relationship between microplastics and surface roughness.
A newly published study in Scientific Reports shows that the anomalies in wave activity are not caused by the plastics themselves, but by surfactants — soapy or oily compounds that are often released with microplastics and that travel and collect in water in a similar way.
Chris Ruf, Frederick Bartman Collegiate Professor of Climate and Space Science at UM and author of the study, explains that a satellite-based tracking tool would be a major improvement over current tracking methods, which rely primarily on patchy reports from plankton trawlers on the net -Microplastics and catch.
“NOAA, the Plymouth Marine Lab in the UK and other organizations are very aware of our work, but we need to be cautious and fully understand the limitations of the system before we deploy it widely,” said Ruf, who also leads CYGNSS. “These new findings are an important step in this process.”
The research team, which included former researchers Yukun Sun and Thomas Bakker, collected the data at UM’s Aaron Friedman Marine Hydrodynamics Lab. Using the facility’s wave pool, they measured the effects of surfactants and microplastic pellets on waves generated both mechanically and by wind from a fan.
They found that for microplastics to affect surface roughness, their concentrations had to be much higher than those typically found even in polluted areas of the ocean. However, surfactants had a pronounced effect. The researchers found that surfactant-laden water required more wind to create waves of a given size, and those waves dissipated faster than in clean water.
Yulin Pan, an assistant professor of naval architecture and marine engineering at UM and corresponding author on the paper, says this initial discovery will spur further research into how surfactants and microplastics interact in the ocean.
“We can see the relationship between surface roughness and the presence of microplastics and surfactants,” Pan said. “The goal now is to understand the precise relationship between the three variables.”
They plan to use a combination of water sampling, satellite observations and computer modeling to build this understanding. Ultimately, they hope to develop a system that would allow governments, cleaning organizations and others to both detect microplastics present and predict how they are likely to migrate through waterways.
Ruf and other members of the team are featured in the documentary Plastic Earth, which examines the extent of plastic pollution and engineering solutions under development.
The research was supported in part by NASA Science Mission Directorate contract NNL13AQ00C.