GREEN turtles are swallowing plastic at twice the rate they did 25 years ago, according to a new study.

The finding is based on data collected across the globe since the late 1980s and analysed by researchers at the University of Queensland.

Study leader and PhD candidate Qamar Schuyler says green and leatherback turtles are eating more plastic than ever before and more than any other form of debris.

The ages of turtles and their habitats are also factors.

"Our research revealed that young ocean-going turtles were more likely to eat plastic than their older, coastal-dwelling relatives," Ms Schuyler said on Friday.

Amazingly, stranded turtles found adjacent to heavily populated New York City showed little or no evidence of debris ingestion.

But all stranded turtles found near an undeveloped area of southern Brazil had eaten debris, Ms Schuyler said.

"This means conducting coastal clean-ups is not the single answer to the problem of debris ingestion for local sea turtle populations."

But she said it was an important step in preventing marine debris input into the ocean.

Ms Schuyler said an estimated 80 per cent of debris comes from land-based sources.

That fact showed how critical it was to manage man-made debris at every point, from its manufacture to the point of a product's consumption.