Does Eating Plastics Really Kill Ocean Animals?

The ocean has long been the end of the pipe for plastic pollution, with ocean wildlife bearing the brunt of the overproduction and overconsumption of single-use plastics. The world now produces more plastics than at any point in history—hundreds of millions of tons each year—and more than 11 million metric tons are flowing into the ocean annually. That is equivalent to more than a garbage truck’s worth of plastics entering our ocean every minute.

How does plastic kill ocean animals?

When swallowed, these plastics can be deadly—causing blockages, twisting organs or even puncturing organ walls. Ingested plastics have been found in nearly 1,300 ocean animal species, including every family of mammals and seabirds, and all seven species of sea turtles. Concern about the ecological implications of plastic-induced death rates has fueled calls for policy solutions at every level of government, from the local to the international. However, it is hard to set policy goals without understanding the measurable risk plastic ingestion poses to these species.

Ocean Conservancy scientists, along with top researchers at the University of Toronto, Federal University of Alagoas in Brazil and the University of Tazmania, worked together to answer the question: how much plastic is too much? They sought to determine how much ingested plastic is likely to cause death in seabirds, sea turtles and marine mammals. In other words, we sought to figure out the actual number of pieces and volume of macroplastics (plastics greater than 5 milimeters) that those animals must have in their gut to cause death 90% of the time.

How much ingested plastic does it take to kill an ocean animal?

We compiled data from more than 10,000 necropsies—animal autopsies—of seabirds, sea turtles and marine mammals collected between the years 1900 and 2023 where we knew both the cause of death and whether and how much plastic the animal had eaten.

The results were alarming. We were surprised by the very small amount of plastic it takes to kill a seabird. We found that rubber (the kind balloons are made from) is the deadliest form of plastic to seabirds when ingested. It only takes six small pieces of rubber—each, on average, smaller than a pea in size—to kill a seabird.

Sea turtles are also surprisingly vulnerable, given their massive size: Less than half a baseball’s worth of plastics is likely to kill one in two Loggerhead turtles. Shockingly, nearly half of all sea turtles in our database had plastics in their guts at their time of death, which is especially troubling when you consider that five of the world’s seven sea turtle species are International Union for the Conservation of Nature (IUCN) red-listed as threatened.

Our models found that marine mammals are especially vulnerable to the impacts of lost fishing debris, also known as ghost gear; when swallowed, with just 28 pieces—each smaller than a tennis ball—enough to kill a sperm whale. Additional key findings from our research for each of the animal groups we studied include:

• Seabirds
  • About 35% of seabirds in our dataset had plastic in their digestive tracts.
  • Roughly 5% of seabirds who had plastics in them died specifically from plastic ingestion.
  • Hard plastics were consumed more frequently than all other material types, followed by soft plastics, fishing debris, rubber and foams.
  • When a seabird consumes only three pieces of rubber, like balloon shreds, our models predict there is a 50% chance this consumption will lead to the animal’s death.
• Marine Mammals
  • In marine mammals, fishing debris was the most frequently ingested plastic material, followed by soft plastics, rubber, hard plastics, foam and cloth.
  • Roughly 12% of marine mammals in our dataset had plastic in their digestive tracts.
  • Nearly 6% of marine mammals from our dataset with plastics inside died as a result of eating those plastics. 
  • When a marine mammal consumes just 12 pieces of soft plastic—like grocery bags—our models predict a 50% chance this action will lead to the animal’s death.
  • Half a soccerball’s worth of soft plastic (by volume) is enough to kill 90% of individuals in most seal, sea lion, dolphin and porpoise species. 
• Sea Turtles
  • In sea turtles, soft plastics like grocery bags were found to be the most frequently ingested plastic material, followed by fishing debris, hard plastics, foams, rubber and cloth.
  • Nearly 50% of individual sea turtles in our dataset had plastic in their digestive tracts
  • About 9% of turtles that ingested plastic in our dataset died as a result of eating it. 
  • Over 4% of all turtles in our dataset died directly from plastic ingestion. 
  • Just 1.5 golf ball’s worth of plastic (by volume) is enough to kill 50% of adult loggerhead sea turtles.

What can this research do?

This research emphasizes the risks macroplastic pollution poses to the life of marine animals, and the risk varies by species and plastic type. Our findings provide key insights to inform future research and policy actions aimed at reducing plastic pollution and the harm it causes to ocean wildlife and ecosystems. These results also underscore that important interventions like beach cleanups and better management of plastic waste are critical for protecting marine species. Because some types of plastics are deadlier than others when swallowed by marine life, policies targeting those specific items (e.g., plastic bags and balloons) can play an important role in protecting vulnerable species from the harms of plastic pollution in the future.

It is imperative to tackle the global plastics crisis by taking actions at all levels, from local to federal to international. In the U.S., bills like the REUSE Act—bipartisan legislation that would require examination and enhancement of existing reuse and refill systems—is just one way to make a difference. Add your name now and call on lawmakers to support and pass the REUSE Act.