Findings in title quoted from the linked summary^1 about research^2 at Danmarks Tekniske Universitet.

From the linked summary:^1

>To collect the samples, the researchers used equipment that can capture far smaller plastic particles than those picked up by the equipment that’s usually used to collect plastic in the oceans.

>This is because the researchers are particularly interested in particles that are so small that copepods—which make up a significant part of the marine food chain—can eat them.

>Specifically, particles that measure less than 300 micrometres (one thousandth of a millimetre) and down to 10 micrometres.

>The researchers found between 25 and 100 microplastic particles per cubic metre of water collected. In the samples with the highest measured concentration, this corresponds to one plastic particle per 10 litres of water.

>By contrast, the samples contained about 100,000 times more plankton than microplastics.

>According to PhD student Gunaalan Kuddithamby, not many studies have used this method—both because it is difficult to collect the samples and because it is expensive and time-consuming to analyse them.

> 

>Video footage from the laboratory experiments shows that in four out of five cases, the copepods spit out the plastic particles.

>“Even though they catch thousands of particles in their tiny mouthparts, they can tell that they’re not food, either because of the structure or taste of the particles.

>“They taste hundreds of particles a minute, but when a plastic particle goes in, they spit it out,” explains Torkel Gissel Nielsen.

>“If they do eat the microplastic particles, we’ve shown in other experiments that they excrete them—just like kids who’ve accidentally eaten small beads,” he says.

>This also means that the microplastics don’t bioaccumulate when the copepods become meals for larger organisms, which in turn are eaten by larger animals, and so on.

^1 Danish waters are filled with plankton, not microplastics, Miriam Meister, 26 Feb. 2023, https://www.dtu.dk/english/news/all-news/danish-waters-are-filled-with-plankton-not-microplastics?id=725e4330-f790-4e43-a2c8-e1518961d4b2

^2 Gunaalan Kuddithamby et al. Abundance and distribution of microplastics in surface waters of the Kattegat/ Skagerrak (Denmark), Environmental Pollution 318, 120853 (2023) https://doi.org/10.1016/j.envpol.2022.120853