Glue-like substances secreted by bacteria are sticking tiny particles of plastic together in the ocean to form larger masses, Scottish research has discovered.
During experiments in seawater, the micro and nano plastics joined with biopolymers made by bacteria to form larger clumps within minutes.
Scientists believe this could lead to the larger items being mistaken for food by marine mammals.
They also fear this could alter the flow of food from the surface to the seafloor, potentially leading to deep sea creatures being starved.
Researchers at Heriot-Watt University in Edinburgh used water collected from the Faroe-Shetland Channel and the Firth of Forth to set up their experiments.
Plastics were added to the seawater and then incubated in conditions simulating the ocean's surface.
Within minutes, the minuscule pieces of plastic grouped together with bacteria, algae and other organic particles.
The scientists are said to have been surprised to discover large masses of biopolymers formed the bulk of these plastic agglomerates.
"This is a first step towards understanding how nanoplastics interact with natural biopolymers throughout the world's oceans," researcher Stephen Summers said.
"The nanoplastics, which are 100-200 times smaller than a bacterial cell, were actually incorporated into the agglomerates, which became visible to the naked eye in our lab experiments.
"The fact that these agglomerates become large enough to see raises concern, as they are likely to be seen as a food source by small marine animals."
Heriot-Watt Professor Ted Henry said the larger masses are "much more complex than simple pieces of plastic".
"Research like this is beginning to fill the gaps in scientists' knowledge, but we need more evidence in order to prioritise and manage plastic pollution effectively," he said.
