Microplastics are being widely ingested by Britain’s marine mammals, scientists say, with samples found in every animal examined in a study.

The research on 50 stranded creatures including porpoises, dolphins, grey seals and a pygmy sperm whale is the most comprehensive analysis of microplastics in the digestive tracts of both wild cetaceans and seals.

“It’s shocking – but not surprising – that every animal had ingested microplastics,” said Sarah Nelms, of the University of Exeter and Plymouth Marine Laboratory (PML), lead author of the research published in the journal Scientific Reports.

The study found that nylon made up more than 60% of the microplastics, with possible sources including fishing rope and nets, clothing microfibres and toothbrush bristles. Polyethylene terephthalate (Pet) and polyester were also widely present. As well as accidental consumption, microplastics are ingested indirectly when predators consume contaminated prey such as fish.

On average, 5.5 particles were found in the guts of each animal, suggesting they pass through the digestive system, or are regurgitated. “The low number of microplastics in their gut at any one time doesn’t necessarily correlate to the chemical burden within their body because the exposure is chronic and cumulative,” said Nelms. “It’s also not yet understood how synthetic particles physically interact with the gut wall as they pass through.”

Dr Penelope Lindeque, the head of the marine plastics research group at PML, has found microplastics in animals at every level of the food chain, from tiny zooplankton to fish larvae, turtles, and now marine mammals.

“It’s disconcerting that plastic is everywhere – all animals are exposed to it and they are ingesting it in their natural environment,” she said. “The ocean is a soup of microplastics and it’s only going to get worse, so we need to reduce the amount of plastic waste released into our seas now.”

Species with a long lifespan such as dolphins and seals are good indicators of marine ecosystem health, but as top predators they are susceptible to the accumulation of pollutants such as toxins or plastics.

Lindeque said: “There’s a risk that chemicals within the plastic and chemicals that stick to the outside of the microplastics, such as PCBs (polychlorinated biphenyls), could affect these animals. We are increasingly worried that microplastics could also be a vector for viruses and bacteria.”

In total, 26 species of marine mammal inhabit or pass through British waters. The 10 species of animals studied were found stranded along the coastline, from Cornwall to the Orkney Islands, and died as a result of disease or trauma, for example as bycatch in fishing nets, interaction with ships or attacks by bottlenose dolphins.

Nelms expressed concern that long-term exposure to plastic pollution could damage the health of Britain’s marine mammals: “They eat all sorts but it will reach a tipping point and really affect their health. It’s important to have this baseline study so we can monitor how they adapt – or don’t adapt – to the changes that are coming.”