Flip-flops and foam slides are among the most disposable shoes we own, and the numbers are stark: 977,000 shoes on one remote island, 370,000 flip-flops on another, and new research showing sandals shed microplastics that fish prefer eating.
When April Burt, a marine biologist at the University of Oxford, arrived on Aldabra Atoll in 2019, she expected plastic. Aldabra is a UNESCO World Heritage Site in the Seychelles — a ring of raised coral so remote that a charter flight or boat is the only way in — and home to more than 150,000 giant tortoises as well as the last flightless bird in the Indian Ocean. What Burt did not expect was the specific form the plastic took. “That was one of the biggest shocks when we actually started cleaning the beaches and the coastline,” she told Mongabay. “You get these big piles, meters high, of just flip flops.”
Over a five-week cleanup, Burt’s team of twelve removed some 60,000 flip-flops. They estimated that more than 370,000 remained, strewn across four islands almost no one visits. Of everything they collected, footwear made up close to a quarter by count. Aldabra is not an outlier. On the Cocos Keeling Islands, another remote Indian Ocean chain of about 600 people, researchers publishing in Scientific Reports in 2019 tallied 977,000 shoes, most of them flip-flops, among 414 million pieces of plastic weighing 238 tonnes. “Islands such as these are like canaries in a coal mine,” the study’s lead author, Jennifer Lavers of the University of Tasmania’s Institute for Marine and Antarctic Studies, said of the find, “and it’s increasingly urgent that we act on the warnings they are giving us.” Remote atolls are useful laboratories precisely because their tiny populations generate almost none of the plastic that lands on them; it all arrives from elsewhere and stays, which is why Lavers told the BBC the findings suggest the world has “drastically underestimated” the scale of the problem.
The most disposable shoe on earth
The flip-flop earns its place at the top of these debris counts because it is the cheapest, most replaceable thing on most feet. It is also, almost always, plastic. Modern sandal soles are made from ethylene-vinyl acetate, polyurethane, neoprene, and polyvinyl chloride, the family of “non-biodegradable synthetic resins” that a 2025 study in the journal Microplastics notes have replaced the leather, wood, and plant fiber that footwear used before the 1960s. Roughly 22 billion pairs of shoes were produced worldwide in 2021, and the summer sandal is engineered to be the most expendable of them. Erin Smith, the chief executive of the Kenyan recycling enterprise Ocean Sole, has watched the consequences wash onto East African beaches for years. “Flip-flops are becoming a significant problem, not just for Kenya,” she told the Mail & Guardian. “They are cheap, therefore affordable to many, and they get dumped once they start to wear away.”
But a sandal does not need to reach the ocean intact to pollute it.
The 2025 Microplastics paper’s authors walked and jogged measured distances in twenty-three pairs of shoes and weighed them along the way; the soles lost mass steadily to abrasion, and across their experiments 75.5 grams of microplastics were shed from the outsoles into the environment. Then they did something more pointed. They cut fragments from sandal soles, dropped them into water, and found that the sandal pieces floated. When they offered those floating fragments to goldfish, the fish ate them, at rates significantly above a control group. Because the sandal fragments float rather than sink, they linger at the surface, which is where the study’s fish encountered and swallowed them. A summer sandal, in other words, sheds plastic particles with every step, and the particles it leaves behind are buoyant enough to sit exactly where fish feed.
This is the same threat the island surveys found hiding beneath the visible piles. On the Cocos Keeling Islands, 93 percent of the plastic was buried up to four inches deep, and 60 percent of what was buried had already broken down into microplastics two to five millimeters across. “It’s the little stuff that’s perfectly bite-sized,” Lavers said. “The stuff that fish and squid and birds and even turtles can eat.” A flip-flop that washes ashore whole is a problem anyone can see. The same flip-flop, ground down by sun, sand, and use into fragments the size of fish food, is the problem almost no one does.
Cleaning it up costs more than the shoe
The economics are lopsided, hitting the places least responsible the hardest. Removing the plastic from Aldabra alone was estimated to cost as much as $7.3 million and 18,000 hours of labor, a bill Burt called out directly. “This eye-watering price-tag makes the economic burden of the unsanctioned import of plastic litter on small island states abundantly clear,” she said.
Not all of that litter is footwear; discarded fishing gear accounted for 83 percent of Aldabra’s plastic by weight, a reminder that the ocean’s plastic arrives from many directions at once. But flip-flops are far more tangible. Beach-bound people buy them wear out, and throw them away by the billions. Ocean Sole has turned some of that burden into livelihoods, employing close to 100 people to carve discarded flip-flops into sculptures; the enterprise says it has recycled more than 695 tonnes of flip-flops since 2006 (a figure that sounds large until it is measured against 22 billion pairs of shoes a year). Julie Church founded the group after finding mounds of flip-flops on a Kenyan beach where children were carving them into toys.
While flip-flops and slides made from recycled plastic, reclaimed ocean waste, or algae-blended foam are sold as the guilt-free eco version, a recycled sandal is still a synthetic-polymer sandal. It abrades into microplastics underfoot exactly as virgin foam does, and if it reaches the sea, it persists there the same way, because recycled content changes where the plastic started, not what it does once it is a shoe grinding against pavement or a fragment floating past a fish. Even upcycling a spent flip-flop into something new only postpones the question, since the material has not stopped being plastic.
Material science offers little relief at the moment, because EVA foam, the springy stuff of the modern slide, is effectively non-recyclable, and the sandals designed to cost almost nothing were never designed to be recovered. That leaves the beaches, and the fish, absorbing the difference. Lindsay Turnbull, a co-author of the Aldabra study, framed what that steady accumulation means for a place like the atoll in terms usually reserved for cultural loss. The scale of the plastic washing up “is unacceptable at this iconic site,” she said, “as it would be if the same amount of plastic rubbish had been allowed to accumulate in one of the world’s great museums or art galleries.”
