More than half of the world's sea turtles are thought to have plastic in their guts as millions of tonnes of rubbish continues to be dumped into oceans each year, CSIRO researchers say.
An analysis of about 1000 turtles found dead on Australian beaches found hundreds of pieces of plastic in the animals' guts.
These included plastic bags, hard plastic fragments, balloons, lolly wrappers and pieces of rope.
"Some of the turtles we studied had eaten only one piece of plastic, which was enough to kill it," Dr Kathy Townsend of the University of the Sunshine Coast said on Friday.
"In one case, the gut was punctured, and in the other, the soft plastic clogged the gut."
Researchers found that once a turtle had eaten one piece of plastic it had a 22 per cent chance of dying and by the time it had ingested 14 plastic items the likelihood of death climbed to 50 per cent.
When the load reaches around 100 pieces, death is certain.
"We knew that turtles were consuming a lot of plastic, but we didn't know for certain whether that plastic actually caused the turtles' deaths," CSIRO Oceans and Atmosphere researcher Dr Chris Wilcox said.
Sea turtles were among the first animals found to be ingesting plastic.
Being able to understand the effect of plastic on them will help scientists determine the impact of the pollution on the global population across all seven species.
The modelling can also be adapted to study other marine animals affected by plastic in the world's oceans.