As much plastic as three sugar cubes. That’s all it takes to kill an Atlantic puffin, according to new research.

Researchers have confirmed what environmentalists have long suspected: it takes very little plastic to kill marine animals. For an Atlantic puffin, eating less than three sugar cubes of plastic means a 90% chance of dying. A loggerhead sea turtle can die from about as much plastic as two baseballs, and a harbor porpoise from about a soccer ball’s worth of microplastics. These are the deadly amounts for animals living in oceans where over 11 million metric tons of plastic are dumped each year.

In the study, one in five animals had eaten plastic: 47% of sea turtles, 35% of seabirds, and 12% of marine mammals. Almost half of these animals were already threatened or endangered species.

This research, published in the Proceedings of the National Academy of Sciences, is the most thorough study yet on how plastic ingestion kills marine life. But even if you never visit the ocean, you should care: the same plastics harming wildlife are building up in our bodies, and new studies link them to heart attacks, strokes, and other health issues.

What Scientists Found

A team led by the Ocean Conservancy studied data from 57 seabird species, seven sea turtle species, and 31 marine mammal species, including whales, dolphins, and seals. They looked at how different types and amounts of plastic were linked to deaths in over 10,000 necropsies of dead sea animals.

“We’ve long known that ocean creatures of all shapes and sizes are eating plastics; what we set out to understand was how much is too much,” the lead author, Dr. Erin Murphy, Ocean Conservancy’s manager of ocean plastics research, said in a statement. “The lethal dose varies based on the species, the animal’s size, the type of plastic it’s consuming, and other factors, but overall it’s much smaller than you might think.”

But at the 50% mortality threshold, at which half the exposed animals die, the numbers are more alarming. On average, less than one sugar cube’s worth of plastic killed one in two of the dead puffins examined. One in two loggerhead turtles with only a baseball-sized volume of plastic in their bodies will die.

Different Plastics, Different Victims

The study found that some types of plastic are especially dangerous to certain animals:

Seabirds are most at risk from synthetic rubber, mainly from balloons. Just six tiny pieces, each smaller than a pea, give them a 90% chance of dying. The rubber gets stuck in their digestive systems and blocks food. “Roughly a third of seabirds that ingested some piece of balloon died from it,” Murphy noted.

Sea turtles are most threatened by soft plastics like bags, which they often mistake for jellyfish. About 342 pea-sized pieces of soft plastic were enough to kill 90% of the turtles studied. “One in 20 sea turtles that we studied died from ingesting plastics,” said Dr. Britta Baechler, Ocean Conservancy’s Director of Ocean Plastics Research. “I wouldn’t take those odds.”

Marine mammals like seals, dolphins, and whales are most at risk from fishing debris, such as lost nets, lines, and gear. Just 28 pieces of fishing equipment, each smaller than a tennis ball, can kill a sperm whale. “One whale actually contained, like, a three-gallon bucket,” Murphy said.

These Plastics Are in You, Too

The same plastics that are killing marine wildlife, like polyethylene from bags and bottles, and PVC from pipes and packaging, are now found in human bodies. The health risks are becoming harder to ignore.

A major 2024 study in the New England Journal of Medicine looked at patients who had surgery to remove plaque from their carotid arteries. Researchers found polyethylene in the plaque of nearly 60% of patients and PVC in about 12% of samples. They also saw plastic shards inside immune cells.

Patients who had microplastics in their artery plaque were 4.5 times more likely to have a heart attack, stroke, or die in the next three years than those without detectable plastics.

Microplastics have now been found all over the human body, including in blood, lungs, liver, placenta, breast milk, and urine. Research shows that particles smaller than 10 micrometers can cross the placenta, possibly exposing unborn babies. A thorough review by UC San Francisco researchers found that microplastic exposure is “suspected” to harm reproductive, digestive, and respiratory health, and may be linked to colon and lung cancer.

How Much Microplastic Do Humans Eat?

You might have heard that people eat a credit card’s worth of plastic—about 5 grams—every week. This number, which came from a 2019 WWF study, has been questioned by researchers using better methods. They found that the average person actually takes in about 4 micrograms of plastic per week, about 25,000 times less than was first thought.

Even with the lower numbers, the findings are still worrying. Research in Environmental Science & Technology estimates that Americans eat 39,000 to 52,000 microplastic particles each year just from food. If you include what we breathe in, the number ranges from 74,000 to 121,000 particles. People who only drink bottled water may swallow an extra 90,000 particles a year compared to those who drink tap water.

Microplastic Volumes In Perspective

The marine wildlife study offers a disturbing frame of reference. Three sugar cubes’ worth of plastic—a volume that could easily accumulate in human tissue over a lifetime of eating, drinking, and breathing—is enough to kill an 11-inch seabird with 90% certainty.

Of course, humans are bigger than puffins and our bodies work differently. Still, the heart study shows that even the amount of plastic we’re exposed to is linked to a much higher risk of serious health problems.

“This research really drives home how ocean plastics are an existential threat to the diversity of life on our planet,” said Nicholas Mallos, vice president of Ocean Conservancy’s Ending Ocean Plastics program. “Eating plastics is just one way that marine life is threatened by the plastic pollution crisis. Imagine the dangers when you also consider entanglement and the everpresent threat of toxic chemicals leaching from plastics.”

These chemicals, such as phthalates, BPA, and many other additives, are known to disrupt hormones in people and are linked to problems like metabolic disorders, reproductive issues, and heart disease.

The Scale OF The Microplastics Problem

An estimated 75 to 199 million tons of plastic waste currently floats in our oceans, and humans toss another 8 to 10 million tons into the seas annually. That’s equivalent to dumping a garbage truck of plastic into the ocean every minute. About 80% originates from land-based sources, traveling through rivers and drainage systems to the sea.

The wildlife study only looked at deaths caused by macroplastics, which are pieces bigger than 5 millimeters. It didn’t include non-lethal health effects. The research on human health mostly focuses on microplastics. Taken together, these studies show that both large and small plastics are dangerous for many species.

What You Can Do

California has some of the world’s toughest plastic laws, including SB 54, which requires a 25% cut in single-use plastics. Most Americans don’t have these protections, but what you do still matters for wildlife and your own health.

“Every year, volunteers collect massive numbers of balloons, plastic bags, straws, food wrappers—items that are lethal to wildlife even in small amounts,” said Allison Schutes, Ocean Conservancy’s Senior Director of Conservation Cleanups. “When you pick up just a few pieces of plastic, you are helping to protect the life of a marine animal.”

To protect wildlife:

• Never release balloons outdoors. They’re among the deadliest items for seabirds. Choose bubbles, flags, or reusable decorations instead.
• Ditch plastic bags. Sea turtles mistake them for jellyfish. Keep reusable bags in your car until it becomes a habit.
• Support fishing gear recycling. Abandoned gear is the most deadly form of plastic pollution for marine mammals. Advocate for buyback programs in coastal communities.
• Join a cleanup. Since 1986, Ocean Conservancy’s International Coastal Cleanup has removed over 400 million pounds of trash from beaches and waterways.

To reduce your own exposure:

• Filter your tap water. Reverse osmosis and solid carbon block filters effectively remove microplastics, and tap water contains far fewer particles than bottled water.
• Never heat food in plastic. Heat accelerates the release of microplastics and chemical additives. Use glass or ceramic.
• Replace plastic cutting boards. Research shows they shed microplastics into food. Wood, glass, or steel is safer.
• Choose natural fibers. Synthetic clothing sheds microfibers during washing that enter waterways and food chains.
• Dust regularly. Indoor air often contains higher concentrations of microplastics than outdoor air, due to synthetic furniture, flooring, and textiles.

To drive systemic change:

• Advocate for policy. Extended producer responsibility programs in Colorado, Maine, Oregon, New Jersey, and Washington offer models for other states.
• Support the global plastics treaty. Over 175 UN member nations are negotiating a binding international agreement.

“Governments around the world are grappling with how to address plastic pollution, and they are looking for science-based targets to inform policy decisions,” said Dr. Chelsea Rochman, associate professor at the University of Toronto and senior author of the wildlife study. “This research provides an important foundation for decision-makers to understand thresholds for risk to better protect biodiversity.”

The combined findings from wildlife deaths and human heart studies show that plastic pollution is more than just an environmental problem. It’s a public health crisis that links the fate of ocean life to our own. Every piece of plastic kept out of the environment helps protect living creatures from its harmful effects.