Science now has definitive proof that plastic debris is killing sea turtles.

Australian scientists analyzed nearly 1,000 turtles found dead and washed up on beaches.

Their study found that once a turtle has 14 plastic items in its gut there was a 50% likelihood that it would die.

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Up until recently, it was unclear as to whether the plastic in oceans directly contributed to turtles dying early.

It's now been confirmed that a sea turtle that has ingested just one piece of plastic has more than a one in five chance of dying, according to a study by researchers at CSIRO Oceans and Atmosphere.

Analysis of nearly 1,000 turtles found dead and washed up on beaches around Australia shows that the more plastic a turtle consumes the greater the likelihood that it will die because of it.

Just some of the plastic removed from the large intestine of a green sea turtle. Kathy Townsend / CSIRO

"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, or whether the turtles just happened to have plastic in them when they died," said Dr. Chris Wilcox, Principal Research Scientist with CSIRO Oceans and Atmosphere.

"In other words, we wanted to know 'How much plastic is too much plastic?' for sea turtles."

The scientists found that once a turtle had 14 plastic items in its gut there was a 50% likelihood that it would cause death. However, that's not to say that a turtle won't die if they consume less than 14 pieces of plastic.

Read more: Cigarette butts are the single biggest source of ocean trash

Sea turtles were among the first animals recorded to be ingesting plastic debris, a phenomenon that occurs in every region of the world and in all seven marine turtle species.

Globally, it is estimated that 52% of all sea turtles have eaten plastic. Determining the effect this is having on turtle mortality is a step forwards for understanding the impact of plastic pollution on sea turtle populations.

"Millions of tonnes of plastic debris is [sic] entering our world's oceans on a yearly basis," said Dr. Wilcox.

"The model we've developed can be adapted to help us understand the impact of plastic ingestion not just on individuals, but whole populations of other endangered marine species as well.

"The better we understand the issue, the better equipped we are to address the problem, and work towards viable, scalable solutions."