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, according to the study, published in Scientific Reports on Thursday.

When the load reaches about 100 pieces, death is certain, the study said.

"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.

Young sea turtles are most vulnerable, the study found, because they drift with currents where the floating debris also accumulate, and because they are less choosy than adults about what they will eat.

Worldwide, more than half of all sea turtles from all seven species have eaten plastic debris, said Britta Denise Hardesty, the paper's senior author and a principal research scientist with the CSIRO in Tasmania. "It doesn't matter where you are, you will find plastic," she said.

Six of the seven species of sea turtles are considered threatened, although many populations are recovering.

AAP, with The New York Times