Tiny pieces of plastic and other debris have been found in all mussels sampled from around the UK coast and supermarkets, researchers have said.
In samples of wild mussels from eight coastal locations around the UK and those purchased from eight unnamed supermarkets, 100% were found to contain microplastics or other debris such as cotton and rayon.
There is "significant and widespread" contamination by microplastics and other debris from human activity in coastal seawater samples, coastal mussels and supermarket-bought mussels in the UK, the study said.
Scientists from the University of Hull and Brunel University London said the results showed microplastics consumption by people eating seafood in the UK was likely to be "common and widespread".
Every 100 grams of mussels eaten contains an estimated 70 pieces of debris, according to the researchers, whose study is published in the journal Environmental Pollution.
More research is needed to find out what the implications of consuming the small amounts of microplastic, they said.
Mussels feed by filtering seawater through their bodies, and are ingesting small particles of plastic and other materials as well as their food.
There was more debris in the wild mussels, which were sampled from Edinburgh, Filey, two sites in Hastings, Brighton, Plymouth, Cardiff and Wallasey, than in the farmed mussels bought in shops.
But mussels from the supermarkets, which came from various places around the world, had more particles in them if they had been cooked or frozen than if they were freshly caught, the study found.
Analysis shows around half of the debris found in the mussels was microplastics such as polyester and polythene and 37% was other debris including textiles such as cotton and rayon which is made from cellulose.
Although microplastics were found in all the samples, seafood is only one way it could turn up in people's diets, as microplastics have been found in other food sources and drinking water, and can even be inhaled, Professor Jeanette Rotchell, of the School of Environmental Sciences, University of Hull, said.
"It is becoming increasingly evident that global contamination of the marine environment by microplastic is impacting wildlife and its entry into the food chain is providing a pathway for the waste that we dispose of to be returned to us through our diet," she said.
"This study provides further evidence of this route of exposure and we now need to understand the possible implications of digesting these very small levels.
"Chances are that these have no implications, but none the less, there is not enough data out there to say there is no risk. We still need to do the studies and show that is the case."
She added: "There are currently regulation of some contaminants in food, in the long term, regulatory solutions to this problem will also be needed."
And, given the proportion of debris such as textiles found in the mussels, she said: "All the conversation is about microplastics, but textiles could also be worth investigation."
Dr Alan Reynolds, deputy director, experimental techniques centre, Brunel University London, said: "Blue Planet has rightly awoken the public to the devastating effects waste plastics are having on the marine environment.
"This paper highlights that the problems are close to home in finding that these same polluting microplastics are now coming back to us in the food in our supermarkets."