Nanoplastics may have trackable metal signatures

Because of their size, nanoplastics are hard to detect in the environment. These ubiquitous pollutants—smaller than 1 µm—form when plastic breaks down. The tiny particles are invisible to the naked eye or under an ordinary microscope, making it challenging to determine where the nanoplastics end up, in what quantities, and the risks they pose.

On Monday in a talk at the ACS Fall 2023 meeting in the Division of Environmental Chemistry, environmental health scientist Mohammed Baalousha of the University of South Carolina discussed a new way to potentially track nanoplastics in the environment. The method involves identifying the metals and metalloids widely used as pigments or fillers in plastics and determining their signatures to use as a clue to identify the nanoplastics’ presence.

Using a mass spectrometry technique, Baalousha and his colleagues characterized the metal content in nanoplastic particles they derived from objects such as plastic straws and bottles, polyethene bags, polysterene foam, and tattered plastic found drifting in the ocean. They found that the metal fingerprints for nanoplastics were distinct from naturally-occurring nanomaterials such as clay or organic materials in the soil. The researchers noted, for example, that nanoplastics from polythene bags were rich in titanium. “We [also] saw different plastic products containing different type of metals and different concentrations and ratios of the metals,” Baalousha told C&EN.

While the study sampled only a handful of plastic products, it’s likely the metal signatures vary widely for hundreds of other plastic products on the market. Alexander Gundlach-Graham, an analytical chemist at Iowa State University who was not involved in the research, said the researchers’ method is unlikely to count nanoplastics in the environment or effectively distinguish the plastic source of each particle. “But they may open an avenue for studying the fate and transport of consumer plastics that are nanoscale.”

Gundlach-Graham added that while the study’s preliminary results are promising, it’s challenging to use single-particle mass spectrometry techniques to determine the metal content in very small nanoplastic particles and those with particularly low levels of metallic fillers or pigments.

Going forward, Baalousha and his colleagues plan to extend their research to include many more plastic products. They’re currently studying nanoplastics in water samples from the arctic to see if the particles’ metal signatures match those measured in the laboratory.