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A Pervasive Threat to Marine Life, Environment, and Human Health
Recent research highlights the alarming extent of microplastic pollution and its detrimental impacts across various domains.
Sam Garcia
December 17, 2025
Studies reveal the lethal effects of ingested plastic on marine animals, identify everyday sources of microplastic contamination, and establish concerning links to human health issues.
Lethal Doses for Marine Life
A study published on November 17, 2025, by the Ocean Conservancy and the University of Toronto in the Proceedings of the National Academies of Sciences quantified the fatal amounts of ingested plastic for marine life. Based on over 10,000 necropsies of seabirds, marine mammals, and sea turtles, the research indicates that lethal doses are often surprisingly small.
Seabirds: Ingesting plastic equivalent to three sugar cubes carries a 90% chance of death. For a 50% mortality rate, less than one sugar cube's worth of plastic can be fatal to species like Atlantic puffins. Rubber pieces, even as small as six pea-sized fragments, pose a 90% lethal risk. Hard plastics are also dangerous, with 25 pea-sized pieces having a 90% chance of death.
Sea Turtles: Consuming approximately two baseballs' worth of plastic can lead to a 90% likelihood of death. For adult green sea turtles, swallowing two golf balls' worth of plastic bags and food wrappers presents about a 50% chance of survival. Soft plastics, such as plastic bags, are particularly vulnerable, with 342 pea-sized pieces having a 90% certainty of being lethal. Sea turtles exhibited the highest mortality rate from plastic ingestion among the studied groups, with 4.4% dying from gastrointestinal obstructions or perforations.
Marine Mammals: Ingesting about a soccer ball's worth of plastic can result in a 90% likelihood of death for species like harbor porpoises. Less than a sixth of a soccer ball's volume can cause a 50% mortality rate. For marine mammals, 29 pieces of any type of plastic (hard, soft, rubber, or fishing equipment) can often be lethal. Fishing debris and soft plastics were identified as most harmful.
The study emphasizes that lethal doses vary by species, animal size, and plastic type. It focused on macroplastics (greater than 5 millimeters) and did not include entanglement or microplastic ingestion impacts. Plastic was found in the digestive tracts of 47% of sea turtles, 35% of seabirds, and 12% of marine mammals examined. Nearly half of the individual animals with ingested plastics were red-listed as threatened species by the IUCN.
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