In a study of dead marine mammals washed up on the shores of Britain, researchers say they were “shocked” to find that every single animal they looked at contained microplastics in their guts.

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Publishing their work in Scientific Reports, the team of marine mammal and plastic experts examined the digestive tracts of 50 animals from 10 species of dolphins, seals, and whales. Tiny, broken down pieces of plastics less than 5 millimeters in length were found in all of them, with their stomachs generally containing a greater number than the intestines.

“It’s shocking – but not surprising – that every animal had ingested microplastics,” said lead author Sarah Nelms in a statement. “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.”

The majority of the particles were synthetic fibers that come from clothing, fishing nets, toothbrushes, and other products made from nylon, with the particles mainly blue and black in color. Other plastic bits were fragments broken down from larger pieces of plastic, such as food packaging and plastic bottles. Overall, the animals died from a variety of causes. Although the researchers note that the animals that died from infectious diseases had a slightly higher rate of microplastics, they cannot “draw any firm conclusions on the potential biological significance of this observation.”

(a) Photographic examples of microplastics found in marine mammal digestive tracts (i) Nylon; (ii) Polyethylene; (iii) Polyethylene terephthalate (PET); (iv) Phenoxy resin along with (b) the proportion of colors (c) and size range. Scientific Reports
Marine mammals are good sentinels of how humans are impacting the marine environment given they are long-lived and high up in the food chain. A study last year found that microplastics are making their way up the food chain from smaller animals ingesting plastics, such as crabs and mussels, to the predatory species hunting them, like seals and whales, in a process called trophic transfer. From work over the years, the team say they have found microplastics in nearly all species of marine animals looked at, “from tiny zooplankton at the base of the food web to fish larvae, turtles, and now dolphins, seals, and whales.”

“This study provides more evidence that we all need to help reduce the amount of plastic waste released to our seas and maintain clean, healthy and productive oceans for future generations,” said Penelope Lindeque, head of the Marine Plastics research group at Plymouth Marine Laboratory.

The scientific community is still unclear what effects plastics – and the chemicals contained in and on them – have on marine mammals, or any animals for that matter. However, previous studies have indicated that marine mammals who mistake microplastics for food have a much higher risk of death, like plastic bag-eating sea turtles and whales dying from blocked digestive tracts. The researchers hope that further research will help people understand how our plastic addiction impacts the world and its many animals.

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