The alarming level of marine pollution is revealed by research that found microplastics, such as fragments of plastic bags and clothing, in species living in depths of over 6,500 feet.

It is now thought that around half of marine creatures living at these depths in the North Atlantic could be eating such material.

Researchers at the Scottish Association for Marine Science (SAMS) at Dunstaffnage north of Oban, sampled deep-sea starfish and sea snails from the Rockall Trough and found microscopic traces of plastic in 48 per cent of those sampled. Worryingly the levels of plastic ingestion were comparable to those found in species living in shallower coastal waters.

Although scientists have previously found traces of microplastics in the deep sea, this research, published in the journal Environmental Pollution, is the first time microplastic ingestion in deep-sea invertebrates has been quantified.

A range of plastics were identified; the paper shows how even naturally buoyant substances, such as polyethylene used to make plastic shopping bags, could be found inside brittle stars, sea stars and sea snails.

Microplastics are small pieces of plastic less than five millimetres in size and, when ingested by sea creatures, may be passed up the food chain.

Polyester was the most abundant plastic identified, mainly in the form of microscopic fibres, and while it is not possible to definitively know its origin, this substance is used widely in clothing and can reach the sea in waste water from washing machines.

Lead author on the paper Winnie Courtene-Jones, a University of the Highlands and Islands PhD researcher based at SAMS, said: “Microplastics are widespread in the natural environment and present numerous ecological threats, such as reducing reproductive success, blocking digestive tracts and transferring organic pollutants to organisms which eat them. More than 660 marine species worldwide are documented to be affected by plastics.

“There is much evidence of microplastics around coastal waters but little is known about the extent of plastic pollution in the deeper ocean.

“The deep sea is the largest, but also the least explored part of the planet and may be the final sink for plastics. More work is needed on the wider ocean environment to understand the long term fate of marine plastic Her supervisor, SAMS deep sea ecologist Dr Bhavani Narayanaswamy, said: “No longer ‘out of sight, out of mind’, research into microplastics is rapidly increasing in importance. We are attempting to establish not only how widespread they are, but also how and where they accumulate in animals, and ultimately the impact that they may have on the health of humans.”