Plastic is all around us—in our landfills, in our oceans, and even in the bellies of some of Earth's most vulnerable creatures. For a new paper in the journal Global Change Biology, researchers checked the guts of 102 deceased sea turtles, some of which belong to critically endangered species, and found that all of them tested positive for microplastics.

For the study, UK-based researchers from the University of Exeter, Plymouth Marine Laboratory, and Greenpeace Research Laboratories studied turtles that had died after being stranded or accidentally caught by commercial fishing operations. All seven marine turtle species were tested, including the endangered green turtle and the critically endangered hawksbill and Kemp's ridley turtles.

The specimens were found off the coasts of North Carolina in the Atlantic Ocean, northern Cyprus in the Mediterranean Sea, and Queensland, Australia in the Pacific Ocean. Necropsies revealed plastic particles under 5mm in length, while microplastic fibers were one of the most common contaminants detected in their guts. These can come from a variety of sources, including clothing, tires, cigarette filters, ropes, and fishing nets. More than 800 synthetic particles were found in the turtles. Only one section of the gut was tested in each animal, so the actual number is likely 20 times higher, according to a University of Exeter statement.

A 2015 study, also in Global Change Biology, estimated that 52 percent of all sea turtles may have ingested microplastics.

"From our work over the years, we have found microplastic in nearly all the species of marine animals we have looked at, from tiny zooplankton at the base of the marine food web to fish larvae, dolphins, and now turtles," Dr. Penelope Lindeque, of the Plymouth Marine Laboratory, said in the statement. "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."

The consequences of ingesting microplastics—via contaminated water or by eating other fish or plants—isn't currently known. The particles are small enough to pass through the gut without causing any blockages, unlike larger plastics which can—and do—wreak havoc on marine life. While the authors concluded that microplastics, at their current levels, post less of a threat than fisheries bycatch and entanglements in fishing gear, they said further studies should be conducted to determine the actual risks.

"They may possibly carry contaminants, bacteria, or viruses, or they may affect the turtle at a cellular or subcellular level," lead author Dr. Emily Duncan of the University of Exeter said. "This requires further investigation."