Deadly dose of plastic – studies reveal the scale of the threat to marine species

The Atlantic puffin (Fratercula arctica) is a charming Arctic bird whose population has been declining for two decades. In addition to climate change and habitat degradation, it is threatened by plastic pollution – scientists from Ocean Conservancy calculated that ingesting just 12 g of plastic can lead to the bird’s death. Similar risks affect thousands of other valuable species inhabiting marine ecosystems.

How much is too much?

Plastic pollution has been discussed and written about for years. The threats posed to aquatic organisms by plastics drifting in the oceans are well known – from suffocation to starvation. Experts from Ocean Conservancy decided to investigate what quantities are actually dangerous for specific species. The study, published on 17 November this year in the Proceedings of the National Academy of Sciences, sheds new light on the plastic-driven ecological disaster.

Researchers analysed over 10,000 animal necropsy results conducted between 1900 and 2021. These included more than 1,500 birds from 57 species, 1,300 sea turtles, and over 7,500 marine mammals. In nearly half of the turtles, one third of the birds, and 12 percent of the mammals, pieces of plastic were found in the digestive tract at the time of death.

Very little is enough

The study showed that plastic pollution affects each species differently, and the lethal dose depends on the organism’s size and the type of plastic. Generally, ingesting between 6 and 405 pieces of macroplastic (larger than 5 mm) results in a 90 percent probability of death. For birds, the greatest threat is rubber; for mammals, soft plastics and fishing debris; and for turtles, both soft and hard plastics.

The South Georgia diving petrel (Pelecanoides georgicus), a small bird inhabiting subantarctic islands, has only a 50 percent chance of survival after ingesting just 0.5 cm³ of plastic. For the wandering albatross (Diomedea exulans), a dangerous dose is around 3 cm³, and swallowing 5 cm³ almost always results in death.

Size is also crucial for turtles – an adult leatherback turtle (Dermochelys coriacea) can ingest more than 140 cm³ of plastic and still have a 50 percent chance of survival, while for a juvenile green turtle (Chelonia mydas), the lethal dose is less than 30 cm³. According to the study’s authors, the youngest turtles are the most at risk because they stay closer to shore and have a less varied diet than adults.

Plastic pollution and biodiversity

Among the species known to ingest drifting ocean plastics and die from it, many are classified as threatened with extinction. Single-use packaging and fishing waste thus become yet another factor reducing the biodiversity of marine ecosystems.

Nicholas Mallos, one of the study’s authors, emphasises that the risks associated with plastic pollution are not limited to death from ingestion. Imagine the scale of the danger if we also consider entanglement in plastic and the pervasive risk of toxic chemicals being released from synthetic materials, he explains.

For nearly 40 years, Ocean Conservancy has been cleaning beaches and waterways. Each year, more than 19 million volunteers take part in these efforts, removing over 1 million kg of plastic waste. Every such action is of immense importance today.

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Bibliography:

E.L. Murphy, B.R. Baechler, L. Roman, G.H. Leonard, N.J. Mallos, R.G. Santos & C.M. Rochman. A quantitative risk assessment framework for mortality due to macroplastic ingestion in seabirds, marine mammals, and sea turtles, Proc. Natl. Acad. Sci. U.S.A. 122 (48) e2415492122, https://doi.org/10.1073/pnas.2415492122 (2025)