Plastic, biogenic particles combine in the ocean, sink to lower depths

New research suggests biological particles can help carry plastic pollution to the seafloor.

The oceans are filled with naturally occurring particles called biogenic particles -- living and dead plankton organisms, as well as their fecal matter. Previous studies showed biogenic particles can combine to form larger lumps called aggregates.

To test how plastic particles interact with biogenic particles, scientists tested the movement patterns of polystyrene beads measuring between 700 and 900 micrometers in a water column. The beads failed to form aggregates on their own. But when combined with biogenic particles, the beads and biological particles quickly coalesced, forming aggregates.

"While microplastic particles alone did nearly not aggregate at all, they formed quite pronounced and stable aggregates together with biogenic particles within a few days," Anja Engel, head of the GEOMAR research group, said in a news release.

In a followup experiment, scientists compared the movements of purified particles and particles coated with a biofilm. The particles coated with a biofilm formed aggregates with biogenic particles more quickly.

"If microplastics are coated with a biofilm and biogenic particles are simultaneously present, stable aggregates of microplastics and biogenic particles are formed very quickly in the laboratory," researcher Jan Michels said.

Scientists suggest the combination of abundant biogenic particles and plastic particles coated in biofilm is common throughout Earth's oceans.

"This is why the aggregation processes that we observed in our laboratory experiments very likely also take place in the oceans and have a great influence on the transport and distribution of microplastics," said researcher Kai Wirtz.

Scientists detailed their analysis of plastic particles this week in the journal Proceeding of the Royal Society B.

Previous studies have shown that micro plastics are ending up in the deep ocean and are being ingested by fish. The latest helps explain how the bits of plastic are making it to the deep sea.