How counting nanoplastics can help clean up the environment

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How counting nanoplastics can help clean up the environment

American researcher Denise Mitrano has been honoured by the Swiss National Science Foundation for her work on micro- and nanoplastics in the environment. Her new tracking method could indirectly help to reduce plastic pollution.

How much plastic is in the water and food we consume everyday? That's the first question I ask Denise Mitrano during a meeting in her office at the Swiss Federal Institute of Technology Zurich (ETH Zurich). I expect an answer along the lines of "a lot" or "too much." But the reality is more complex.

"Before we can say how much plastic is in a glass or on a plate, we need to be able to measure it," says the geochemist and assistant professor. "Plastic particles can be extremely small in size and escape current analytical tools."

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An innovative tracking method could now open new avenues. The procedure developed by Mitrano makes it possible to track how micro- and nanoplastics – fragments of a few millionths of a millimeter – spread through water, soil and living organisms.

"I've always wanted to find solutions to problems,” she says, referring to her previous research. “I was inspired by methods I've developed to measure metal nanoparticles."

denise mitrano
 Denise Mitrano is an assistant professor of environmental chemistry at the federal technology institute ETH Zurich. ETH

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Mitrano's solution involves chemically adding metals to plastic nanoparticles. These are precious and inert metals, such as palladium or indium, which act as markers. This means that the nanoparticles become visible. "The advantage is that they [the metals] can be measured much more accurately and quickly than plastic."

The process was applied to study the effectiveness of a sewage treatment plant in removing microscopic plastic particles in water. "The good news is that more than 95% of nanoplastics and microplastic fibers are removed," says Mitrano.

However, this does not solve the problem of plastic pollution. "Nanoplastics accumulate in sewage sludge,” the scientist points out. “In Switzerland they are incinerated, but in other countries they are used to fertilise fields."

Mitrano also analysed whether a drinking water treatment station can purify water contaminated with nanoplastics. For this, she recreated some of the purification stages used at Zurich's plant. "Slow filtration using sand filters proved particularly effective," she says.

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