ATHENS, Greece (AP) — Scientists say a study of whales and dolphins that have washed up dead in Greece over a 20-year period has found alarmingly high levels of plastic trash in the animals' stomachs, which can condemn them to a slow and painful death.

In the worst case, a 5.3-meter (17-foot) young sperm whale beached on the Aegean island of Mykonos had swallowed 135 plastic items weighing a total of 3.2 kilograms (7 pounds). This blocked its stomach, while the animal had starved to death.

Sperm whales are an endangered species at high risk in the Mediterranean from deadly collisions with ships, entanglement in drift fishing nets and noise pollution from oil and gas exploration.

The study published in the Marine Pollution Bulletin found that sperm whales were also the species worst affected by plastic ingestion.