Measuring nanoplastics

I remember the day when my colleague, Dusan Materic, came up with the idea to use our proton-transfer-reaction mass spectrometer (PTR-MS) to measure sub-micron plastic particles, so called nanoplastics, in the snow samples that we collected at the top of the Mt Hoher Sonnblick in Austria. This was about three years ago. Plastic as an environmental problem was starting to hype. I was well aware of the problem in the ocean, but it dawned on many scientists (including me) that this problem may not be confined to the ocean alone.

I was immediately excited because it could work – and if, it would be a world premiere: the first instrument capable of quantifying sub-micron plastics with unprecedented sensitivity. But what a task! One cannot pour plastic in the mass spectrometer and get a clear answer. Samples need to be heated, so that the vapours can be transported into the instrument with a carrier gas. Luckily this setup was already developed: we use it to measure organics in snow samples with the original goal to learn about aerosol deposition and possibly about past climates when analysing ice-cores. The first pilot studies revealed that even in what were thought to be pristine samples we identified hundreds of different organic ions. Could some of these be attributed to nanoplastics?

Answering this question was hard work. We investigated pure samples of the most commonly used plastics and evaporated them into the PTR-MS, thus recording the unique fingerprint - typically hundred different ions - for each plastic type. More questions arose: how many of these fingerprint ions are needed to retrieve a plastic signal from samples? How to avoid false positive and false negative attributions? How to deal with carry-over contamination when analysing many samples in a row? How to deal with the background signal? What if fingerprint ions have additional sources, e.g. from organic aerosol without any relation to nanoplastics? And many more… These issues are complex. Dusan managed to cast all the analyses in smart algorithms that allow for a reliable and quick analysis of nanoplastics in different samples ranging from Greenland firn-core to Antarctic sea-ice samples.

Surprisingly, we found that nanoplastics are almost everywhere! Polystyrene (PS), polyethylene (PE), and polyethylene terephthalate (PET) to mention just a few are found at locations where they should not be. Nanoplastics are small enough so that they can be transported in the air over large distances. They can be inhaled by mammals and other animals, and directly enter the blood stream through the pulmonary alveoli. While this is concerning, at the same time I experience excitement and delight about the method and about what we were able to achieve. But when looking at the bigger picture, I am saddened to see how humans once again impact (and possibly harm) nature in yet another unintended way.

Rupert Holzinger