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School Workshops: Oysters and Microplastics

Preventing Plastic Pollution partners IFREMER and the CNRS (working within the LEMAR centre) have set-up workshops for primary and secondary school pupils, and the general public to raise awareness of the impact of plastic pollution on marine organisms. The workshops aim to explain the problem of plastic waste found at sea, and especially the invisible pollution caused by microplastics (less than 5mm) which account for more than 90% of plastic waste in the sea. And these are not devoid of toxicity.

In order to offer students an understanding of the scientific approach we use, we install the experiment with them, putting shellfish (often oysters) in see-through containers with seawater, microalgae (their food) and microplastics (polyethylene) of an ingestible size (10 to 45 µm) and red/orange in colour. This shows participants what oysters eat, and allows them to ask questions/hypotheses related to the experiment.

After leaving the animals to settle in their container for a few hours, we return : the students then start their observations and try to draw conclusions about what happened during those few hours.

Three observations are often made:

  • The oysters are slightly open. The oysters yawn and as they are approached, they close quickly, in response to the vibrations. This is a sign that they were active, that they had to breathe and filter the water.
  • The addition of microalgae, at the beginning of the experiment, had coloured the seawater a light brown-green. The colour of the seawater has become translucent again. This is proof that the animals filtered the sea water and held the microalgae in their gills (a kind of miniature net) to collect them in their mouth and eat them.
  • A red orange net comes out on the side of the oyster (Fig. 2). This corresponds to their excrement and is proof that the oysters ingested the microplastics (so they were not able to avoid them), and that these microplastics followed the transit of the digestive tract. When ingested, microplastics can either obstruct the digestif system or simply pass through it and what we have observed in this workshop is also what we commonly observe in the lab.

This experiment allows us to explain to students that even the simple transit of microplastics through the digestive tract can induce major changes in the biology of the animal that ingested them.

Impacts on the animals include changes in digestion that disrupt the energy input via food and a direct source of stress, with consequences for their growth, defenses, and reproduction. And, plastics are made up of additives/plasticisers, which can be released into the digestive tract during transit and cause chemical toxicity, such as endocrine (hormones) disruption.

The visual and hands-on nature of this workshop has the merit of being memorable for participating students, who will then go on to explain it to their family and friends, and in turn become active in sharing knowledge and raising awareness of the need for more and better protection of our oceans.