Microplastic has been found inside 50 dolphins, seals and whales that had washed up on Britain's shores.
Researchers from the University of Exeter and Plymouth Marine Laboratory examined 50 mammals, including 10 species of dolphin, seals and whales, and found microplastics in them all.
Eighty-four per cent of the particles found inside the creatures were synthetic fibres, which can come from clothes fishing nets and toothbrushes.
Sixteen per cent of the plastic particles were fragments which could have come from food packaging and plastic bottles.
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Lead author of the study, Sarah Nelms, said the find was "shocking" but "not surprising".
"The number of particles in each animal was relatively low, an average of 5.5 particles per animal, suggesting they eventually pass through the digestive system, or are regurgitated," she said.
"We don't yet know what effects the microplastics, or the chemicals on and in them, might have on marine mammals."
Though the animals in the study died of a variety of causes, the study showed that those that died due to infectious diseases had a slightly higher number of particles than those that died of injuries or other causes.
The report has been published in the journal Scientific Reports.