The ocean is overrun with plastic…over 171 trillion piecesscientists have calculated, and is constantly growing. Animals become entangled in or ingest plastic, the chemicals released by the material are often toxic, and once inside a creature, the plastic can remain inside it, potentially blocking its respiratory tract or intestines.
A binding global treaty regulating the production and disposal of plastic could help change this. Although the last round of negotiations on such a treaty ended unsuccessfully in August 2025.that hasn't stopped scientists from wondering how it might work. The treaty would benefit from numbers backed by evidence of how deadly plastic is to marine life, and so a team of researchers publishing in the magazine Proceedings of the National Academy of Sciences studied the results of more than 10,000 autopsies of sea turtles, seabirds and mammals. They found that while the definition of how much plastic is lethal can vary between creatures, the numbers are often alarmingly low.
Based on reports of animal deaths going back more than a century, researchers determined how many plastic creatures ingested and whether that plastic was the cause of their deaths. They then calculated how much plastic was associated with a 50 percent chance of death and how much was associated with a 90 percent chance of death, said Erin Murphy, ocean plastic research manager at the Ocean Conservancy and co-author of the study. They also looked at different types of plastic to determine which was most dangerous to different animals.
“I was surprised by some of the thresholds we found,” Murphy says. According to the team's calculations, if a bird the size of an Atlantic puffin ate just under 3 plastic sugar cubes, it had a 90% chance of dying from exposure to the plastic. For a loggerhead sea turtle, this amount would be about the same as a couple of baseballs.
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The team found that rubber materials were particularly dangerous to birds. “For seabirds, just six pieces of rubber, like a balloon, each on average smaller than the size of a pea, have a 90% chance of causing death,” Murphy says. (Although rubber may be a natural product, most rubber used today is synthetic and may be regulated by the plastics treaty.)
The analysis focused on situations where plastic was clearly to blame for an animal's death—for example, when it blocked an airway, ruptured a stomach, or caused an intestinal rupture. It's likely that plastic causes other, less obvious problems for sea creatures, such as making them feel full even if they haven't eaten enough to survive.
“It's sad and difficult to think about, but it's also a reminder that everyone can be part of the solution,” Murphy says. “And if we're going to really solve this problem, the science is clear. We need to reduce the amount of plastic we produce, improve collection and recycling, and clean up what we already have, and that's really something that everyone can participate in.”
To reduce the amount of plastic in your life, consider using solid bars of shampoo and conditioner instead of buying plastic bottles, buying fruits and vegetables loose rather than packaged in single-use plastic, and beware of plant-based plastic alternatives.they are often not as eco-friendly as you might hope.
“And pick up any plastic you see on your daily walk,” Murphy suggests. Every part that lands in the right place is one less part that could end up in the sea turtle.
