Plastic ingestion: Study reveals ‘lethal dose’ for marine wildlife

By Aysu Bicer

LONDON (AA) - A major international study has, for the first time, estimated how much plastic it takes to kill seabirds, marine mammals and sea turtles, offering a stark new insight into the global impacts of ocean pollution.

Researchers analyzed more than 10,000 animal necropsies, compiling one of the largest datasets of its kind.

Their findings, published in the Proceedings of the National Academy of Sciences, show that between 6 and 405 pieces of macroplastic can give an animal a 90% chance of dying, depending on the species and the type of plastic consumed.

The study revealed striking differences across animal groups.

A 90% mortality risk was linked to around 23 pieces for seabirds, 29 pieces for marine mammals, and up to 405 pieces for sea turtles. The size and material of the plastic also mattered: rubber items were especially dangerous for seabirds, soft plastics and fishing gear posed the greatest risk to marine mammals, while hard and soft plastics were most lethal to turtles.

Plastic ingestion has already been documented in nearly 1,300 marine species, from tiny seabirds to humpback whales. But quantifying the risk has been difficult, as animals typically die from sudden blockages or injuries rather than long-term exposure.

The researchers used a specialized statistical model to capture how different types of plastic increase the likelihood of a fatal outcome.

Overall, the study found that 35% of seabirds, 12% of marine mammals, and 47% of sea turtles had ingested plastic, with a smaller but significant proportion dying directly from it.

Scientists say the results could help governments develop clearer thresholds for when plastic pollution becomes dangerous, strengthening calls for global action.

The authors hope their work will inform future monitoring systems and guide international policies to curb plastic pollution entering the ocean.