MICROPLASTICS IN SHELLFISH: AN IZSAM STUDY ON ACCUMULATION AND DEPURATION

Oysters, bivalve molluscs and highly efficient filter feeders, can ingest microplastics: fragments smaller than 5 millimetres that result from the breakdown of plastic waste. Once these particles accumulate in their tissues, they can also end up on our plates, becoming a potential route of contamination for humans. A study published in the journal Water by a group of researchers from the Istituto Zooprofilattico Sperimentale dell’Abruzzo e del Molise (IZSAM), in collaboration with the Institute for the Study of Anthropogenic Impacts and Sustainability in the Marine Environment (IAS-CNR), investigated in the laboratory what happens when oysters are exposed to these particles, and how they eliminate them.

To replicate realistic conditions, microplastics of different shapes and polymers were used (polypropylene fibres, polystyrene beads, polyethylene terephthalate fragments), artificially aged to form a biofilm and make them as similar as possible to those found in the natural environment. The oysters were kept for 28 days in tanks with synthetic seawater containing these particles. This procedure, known in scientific terms as “exposure”, involves placing animals in direct and continuous contact with a specific substance in order to study its effects. At the end of this period, the oysters contained on average more than 5 microplastic particles per gram of tissue. Most of them were fibres (79%), followed by beads (19%) and fragments (2%).

Afterwards, the oysters were transferred to clean synthetic seawater to simulate the depuration phase: a treatment required in dedicated centres for all molluscs before they are placed on the market. This process is normally used to eliminate bacteria and other pathogens, but it can also have an effect on microplastics.

“We observed a significant reduction in microplastics, around 69%, within the first 24 hours - says Sara Recchi, marine biologist at IZSAM - and an overall decrease of 92% within five days from the start of the depuration period. The particles that were not easily eliminated were mainly the larger ones or those with more complex shapes, such as longer fibres”.

The study also looked at another aspect: the possible effects of microplastics on oysters at the cellular level. To do this, the researchers analysed several so-called “reference genes,” which maintain stable activity levels even under stress. These genes are not involved in the stress response, but serve as a benchmark to assess the behaviour of others that may become activated or suppressed in the presence of pollutants.

“Choosing stable genes is essential to accurately measure any biological effects caused by microplastics - explains Federica Pizzurro, researcher at IZSAM - Only with a reliable reference can we assess whether other genes, for example those linked to stress response, change their expression”.

The research provides new insights to help improve seafood safety and quality. The results show that well-conducted depuration can effectively reduce the presence of microplastics, even if not entirely. Its success also depends on key practical measures, such as using plastic-free materials, filtered water and covered tanks to prevent further contamination. These practices are already adopted in several countries and could, in the future, be highlighted through dedicated labels. This would be a mark of quality that some consumers are willing to pay for.

Finally, the study suggests that the use of molecular indicators could become a valuable tool for monitoring the long-term environmental effects of microplastics on marine organisms.