Scientists have found levels of microplastic pollution on beaches around Scapa Flow in Orkney are similar to those in industrialised areas like the Forth and Clyde.
Researchers at Heriot-Watt University in Edinburgh took more than 100 sediment samples from 13 beaches on Hoy and the Orkney mainland.
Some plastic is believed to come from clothes which contain polymer fibres.
These are not caught by washing machine filters or at treatment works.
The micro-particles are thought to have been blown up the east coast.
Although more work is needed, researchers say plastic is carried on complex tidal flows through the Pentland Firth, with Scapa Flow acting like a giant sieve capturing the particles.
Dr Mark Hartl, from Heriot-Watt, said: “The fact that a relatively remote island has similar microplastics levels to some of the UK’s most industrialised waterways was unexpected, and points to the ubiquitous nature of microplastics in our water systems.