A new mechanism for microplastics to enter the food chain

Microplastics enter plankton aggregates, which are then ingested by fish and move up the food chain. Scientists from the IMRCP laboratory, LAAS and TBI were the first to use atomic force microscopy to study the problem. In an article published in the journal Science of the Total Environment, they confirmed the existence of one mechanism where the presence of microplastics promotes the aggregation of microalgae, and discovered a second, previously unknown one.

Plastic pollution affects all environments. In particular, microplastics enter the marine food chain and then make their way up to larger animals and humans. Interactions with plankton appear to be particularly important, but are still poorly understood. Microalgae, which make up most of the plankton and the first link in the aquatic food chain, can aggregate under certain conditions. Microplastics cause these aggregates to form, in which they mix and thus pass into the animals or spread to the depths of the oceans. Indeed, the heavier aggregates sink instead of floating.

The researchers have shown that microplastics reinforce the formation of plankton aggregates in two different ways, with which they then mix. This research work is based on a new methodology, centred on an atomic force microscope.

Microalgae emit extracellular polymeric substances (EPS), a combination of carbohydrates, proteins and nucleic acids that they use to colonize solid surfaces and cause them to aggregate. The scientists confirmed that the presence of microplastics enhanced EPS production. This had already been observed, but the team also showed that, even if all the EPS were removed, the microalgae still aggregated more in the presence of microplastics. This time, it is the direct contacts, through hydrophobic interactions between the microplastics and the cell wall, that cause the phenomenon. Part of the team is now studying whether micro- and nanoplastics, once ingested by animals or humans, can be assimilated by the body and what consequences this may have on health.

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2024 Softmat