Precious metal detects minute plastic particles

What would be more valuable precious metal or plastic? One thing is for sure: over 98 percent of nanoplastics are retained in sewage sludge. Researchers were able to prove this because they incorporated the precious metal palladium as a tracer in artificial miniature plastic.

However, a lot of microplastics literally end up in the environment. The researchers' innovative method therefore has great potential to track down the behavior of nanoplastics in technical systems and in the environment in other cases as well.

How much nanoplastic gets into the environment?

Tiny plastic particles in the order of 100 nanometers (millionths of a millimeter) are used in many products, for example to encapsulate colorants or fragrances or as additives in shampoos and cosmetics. Many of them end up directly in wastewater while the product is still in use. Together with other plastics, such as those from tire wear via road drainage, they end up in wastewater treatment plants. But until now, it has not really been possible to measure them there. Unlike larger particles (microplastics), they cannot simply be sifted out and weighed or counted. So - apart from model calculations - it was also not clear how much nanoplastic is retained in wastewater treatment plants and how much of it ends up in the environment.

Now has

n: To this end, they have produced plastic particles in whose core they have incorporated the precious metal palladium. This can be analyzed relatively easily using standard methods. In their paper published today in the journal nature nanotechnology, the researchers show how they used it to successfully study the behavior of nanoplastics in the activated sludge process of a wastewater treatment plant on a laboratory scale.

According to project manager Denise Mitrano, the nanoplastic particles are bound very quickly to the sewage sludge flocs; in the end, the elimination is over 98%. "So as long as the sewage sludge is not taken to the fields, but incinerated as it is in Switzerland, very little nanoplastics end up in the environment," Mitrano says.

That is a positive finding. Still, Mitrano is clear: "We need to know much more about the behavior of nanoplastics. Even if only a small percentage ends up in the waters, it can add up to higher concentrations downstream." She now hopes that her method with trackable particles will quickly lead to new findings. Because the palladium is securely bound inside the nanoplastic, she says, it would even be possible to track whether the specially produced particles are ingested by organisms, and controlled ecotoxicity tests could be conducted. Several projects using the labeled particles are already underway, including a joint project between Eawag and Zurich Water Supply on the retention of nanoplastics in drinking water treatment.