Small crustaceans can fragment microplastics into pieces smaller than a cell within 96 hours, a study has shown.
Until now, plastic fragmentation has been largely attributed to slow physical processes such as sunlight and wave action, which can take years and even decades.
Environmental scientists at University College Cork (UCC) in Ireland studying the 2cm-long amphipod Gammarus duebeni found that microplastic beads were not only ingested but were also fragmented incredibly quickly into nanoplastics.
Because these fragments are small enough to pass through cell membranes, it is thought they are likely to be potentially more damaging to wildlife than microplastics of up to 5mm in size.
Dr Alicia Mateos-Cárdenas, the lead author of the research published in Scientific Reports, said that her findings were “completely unexpected”.
“When I started studying this three years ago, it sounded so crazy that such small animals could be fragmenting plastics but our research shows that plastic fragments comprised nearly 66% of all observed microplastic particles accumulated in the guts of these animals.”
Mateos-Cárdenas used spherical microbeads of polyethylene, the common polymer found in plastic bottles. Each microbead had been tagged with a fluorescent dye so ingestion and fragmentation could be tracked using a microscope.
The study showed that these microbeads were broken down by the crustaceans into nanoplastics that measured less than one micron, or one thousandth of a millimetre.
More fragments were found when the amphipods were exposed to high concentrations of microplastics for four days. The proportion of smaller plastic fragments was at its highest when the amphipods had been purged in pure water in the presence of their food, a plant material, indicating that biological fragmentation could be closely related with the feeding process.
“We saw that the amphipods ingest these plastic particles, grinding them with their mandibles [jaws] as they eat them and pass them on to the digestive system but we don’t yet understand how these animals break down the plastic. We need to investigate the actual mechanism of this biological fragmentation,” said Mateos-Cárdenas.
The research has wider implications because this crustacean is one of more than 200 Gammarus species found globally in rivers, estuaries and oceans.
“This definitely adds an extra layer to our understanding of the fate of plastics in the environment,” said Mateos-Cárdenas. “Once plastics reach rivers and oceans, we don’t really know what happens to them. If animals are ingesting and fragmenting them, the problem is amplified.”
Not only could this biological fragmentation be a global issue, but the harmful effects of plastic contaminants might increase as the particle size decreases.
“If nanoplastics can go through cell [membranes] they could possibly accumulate in animals and plants with unknown potential negative effects … so the plastic pollution issue becomes much more complex and more worrying,” said Mateos-Cárdenas, who explained that “trophic transfer” occurs when predators such as birds or fish eat Gammarus crustaceans.
This means nanoplastics could accumulate further up the food chain, including potentially in humans, while toxic chemicals could potentially cling to the surface of these nanoplastics.
