\u201cThat lethal dose is much smaller than we expected,\u201d lead author Erin Murphy, manager of ocean plastic research at the Ocean Conservancy, told Mongabay.<\/p>\n
She and her co-authors were only looking at \u201cacute mortality events,\u201d which occurred when the animal\u2019s gastrointestinal tract was perforated, cut or obstructed by plastic, preventing movement of food through the stomach and intestines.<\/p>\n
\u201cIt\u2019s harder to quantify the potential deadliness of the longer-term chronic exposure of plastic ingestion with these types of studies,\u201d Murphy explained. \u201cBut I think a key point is that our numbers are only focusing on acute mortality events from plastic ingestion. So as a result, it\u2019s likely an underestimate of the actual existential threat that plastic pollution poses to ocean wildlife, because we\u2019re not considering chemical exposure, we\u2019re not considering chronic exposure, and we\u2019re not considering entanglement.\u201d<\/p>\n
Even excluding these other kinds of plastic exposure, the study, published Nov. 17 in PNAS, found that relatively small amounts of ingested plastic could be deadly. For instance, seabirds such as the Atlantic puffin (Fratercula arctica) only had to consume about three sugar cubes\u2019 worth of plastics to have a 90% chance of death. Sea turtles such as the loggerhead (Caretta caretta), which can weigh about 124 kilograms (275 pounds), needed to consume more than two baseballs\u2019 worth of plastics, while various marine mammal species, including harbor porpoises (Phocoena phocoena), which can weigh about 58 kg (130 lbs), had to consume about a soccer ball\u2019s worth of plastics to have a 90% chance of death.<\/p>\n
The research also identified the plastic categories deadliest to these animals. For seabirds, it was synthetic rubber; for sea turtles, it was soft plastics (such as plastic bags and wraps); and for marine mammals, it was discarded plastic fishing gear.<\/p>\n
The study determined that one in five of the studied deceased animals had consumed plastic, accounting for nearly 50% of the studied sea turtles, 35% of the seabirds, and 12% of the marine mammals. Notably, nearly half of the studied species were on the IUCN Red List, with classifications ranging from near threatened to critically endangered.<\/p>\n
\u201cThese are species that are already vulnerable,\u201d Murphy noted. \u201cTheir populations are already at risk, and plastic ingestion is another thing that is impacting these already stressed species.\u201d<\/p>\n Study co-author Lauren Roman, a marine scientist at the University of Tasmania in Australia, told Mongabay the research \u201cidentifies some important patterns, such as the proportion of different animal groups that die from plastic and the volume of different types of materials likely to be lethal.\u201d<\/p>\n She added the findings can help \u201cshape evidence-based policies\u201d to reduce high-risk plastic items \u2014 ranging from single-use plastic bags and food wrappers to fishing debris \u2014 from entering the marine environment and impacting animals there.<\/p>\n While the study\u2019s findings focus on mortality events, Brendan Godley, a conservation scientist at the University of Exeter, U.K., who wasn\u2019t involved in the research, noted the resilience seen in some species, despite consuming plastic. For instance, he \u201cmarveled at the robustness of sea turtles with over 100 plastic pieces being tolerated by 50% of individuals.\u201d<\/p>\n \u201cI suspect this threshold will increase as further data from more polluted parts of sea turtle habitats are included in subsequent studies,\u201d Godley told Mongabay. \u201cIn the Mediterranean, we often encounter juvenile green turtles with extremely high burdens that have been otherwise healthy until bycaught in fishing nets.\u201d<\/p>\n Godley said the study provided a \u201cfantastic step towards quantitatively assessing the likelihood of mortality due to plastic ingestion in seabirds.\u201d<\/p>\n \u201cGiven the ubiquity of the plastic threat, it is important to start to understand the likely impacts to individuals,\u201d he said, \u201cso that we can understand the likely implications for different populations, and subsequently whole species.\u201d<\/p>\n Murphy, E. L., Baechler, B. R., Roman, L., Leonard, G. H., Mallos, N. J., Santos, R. G., & Rochman, C. M. (2025). A quantitative risk assessment framework for mortality due to macroplastic ingestion in seabirds, marine mammals, and sea turtles. Proceedings of the National Academy of Sciences, 122(48). doi:10.1073\/pnas.2415492122<\/p>\nCitation:<\/h2>\n