Microplastics have been found in the guts of every marine mammal examined in a study of animals washed up on Britain’s shores, scientists say.

Researchers from the University of Exeter and Plymouth Marine Laboratory (PML) in the U.K. examined 50 animals from 10 species of dolphins, seals and whales — and found microplastics in them all.

Most of the particles (84%) were synthetic fibres — which can come from sources, including clothes, fishing nets and toothbrushes — while the rest were fragments, whose possible sources include food packaging and plastic bottles.

“It’s shocking, but not surprising that every animal had ingested microplastics,” said Sarah Nelms, of the University of Exeter and PML.

“The number of particles in each animal was relatively low (average of 5.5 particles per animal), suggesting they eventually pass through the digestive system, or are regurgitated,” Ms. Nelms.

“We don’t yet know what effects the microplastics, or the chemicals on and in them, might have on marine mammals,” she said.

“More research is needed to better understand the potential impacts on animal health,” she added.

Though the animals in the study died of a variety of causes, those that died due to infectious diseases had a slightly higher number of particles than those that died of injuries or other causes.

“We can’t draw any firm conclusions on the potential biological significance of this observation,” said Brendan Godley, of the University of Exeter.

“We are at the very early stages of understanding this ubiquitous pollutant. We now have a benchmark that future studies can be compared with,” said Mr. Godley.

“Marine mammals are ideal sentinels of our impacts on the marine environment, as they are generally live long and many feed high up in the food chain. Our findings are not good news,” he said.

“It is disconcerting that we have found microplastic in the gut of every single animal we have investigated in this study,” said Penelope Lindeque, from PML.

In total, 26 species of marine mammal are known to inhabit or pass through British waters. The species in this study included Atlantic white-sided dolphin, bottlenose dolphin, common dolphin, grey seal, harbour porpoise, harbour seal, pygmy sperm whale, Risso’s dolphin, striped dolphin and white-beaked dolphin.

Researcher Aviad Scheinin says the hundreds of sharks flocking exclusively to the Hadera power plant every winter qualifies as “a legitimate and rare phenomenon.”