Pan: 'We can see the relationship between surface roughness and the presence of microplastics and surfactants'

Researchers from the University of Michigan have made a significant breakthrough in tracking microplastics from space.

By analyzing data from the Cyclone Global Navigation Satellite System (CYGNSS), the team discovered a correlation between the presence of microplastics, tiny flecks that can ride ocean currents hundreds or thousands of miles from their point of entry, and changes in the ocean's surface roughness, according to a February news release from the University of Michigan.

“NOAA, the Plymouth Marine Lab in the U.K. and other organizations are very aware of what we’re doing, but we need to be cautious and fully understand the system’s limitations before putting it into widespread use,” Frederick Bartman Collegiate Professor of Climate and Space Science Chris Ruf said in the release. “These new findings are an important step in that process.”

This finding offers a promising new method for monitoring the movement of microplastics and improving prevention and clean-up efforts, the release said. The research, published in Scientific Reports, highlights the importance of surfactants, soapy or oily compounds that accompany microplastics, in altering wave activity. 

Further exploration of this relationship will provide valuable insights into the interaction between microplastics, surfactants and the ocean environment, according to the release.

Reportedly, satellites are best at spotting soapy or oily residue, and microplastics appear to tag along with that residue, the release said. Microplastics can harm sea life and marine ecosystems, and they’re extremely difficult to track and clean up. 

However, a 2021 discovery raised the hope satellites could offer day-by-day timelines of where microplastics enter the water, how they move and where they tend to collect, for prevention and clean-up efforts, according to the release.

The team noticed that data recorded by CYGNSS, showed less surface roughness — fewer and smaller waves — in areas of the ocean that contain microplastics, compared to clean areas, the release said. 

In preliminary testing, they used the technique to spot suspected microplastic releases 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 Ocean where microplastic collect in massive quantities, the release reported. But until now, the team was unsure about the nature of the relationship between microplastics and surface roughness. 

A newly published study in Scientific Reports shows the anomalies in wave activity are caused not by the plastics themselves, but by surfactants — soapy or oily compounds that are often released along with microplastics and that travel and collect in similar ways once they’re in the water, the release said. The research team, which also included former naval architecture and engineering graduate researchers Yukun Sun and Thomas Bakker, gathered the data at U-M’s Aaron Friedman Marine Hydrodynamics Lab. 

Using the facility’s wave tank, they measured the effects of surfactants and microplastic pellets on waves generated both mechanically and by wind from a fan, according to the release.

They found that, in order for microplastics to affect surface roughness, their concentrations had to be much higher than those typically found even in polluted areas of the ocean, the release said. Surfactants, however, had a pronounced effect. 

The researchers found surfactant-laden water required more wind to generate waves of a given size, and those waves dissipated more quickly than they would in clean water, the release reported.

“We can see the relationship between surface roughness and the presence of microplastics and surfactants,” Yulin Pan, U-M naval architecture and marine engineering assistant professor, said in the release. “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 that understanding, the release said. Ultimately, they hope to develop a system that governments, cleanup organizations and others can use to both spot existing microplastics and predict how they’re likely to travel through waterways. 

Ruf and other members of the team are featured in the documentary Plastic Earth, which explores the scale of plastic pollution and engineering solutions in development, according to the release. The research was supported in part by NASA Science Mission Directorate contract NNL13AQ00C.