Researchers from the Sea Education Association have removed tens of thousands of plastic fragments from the Atlantic Ocean over the past six weeks in what many believe is just a small part of a giant collection of debris in the middle of the ocean.

In their search for marine pollution, crew members of the expedition found more than 48,000 plastic fragments, most no larger than a pencil eraser, of the type of plastic used in bags, straws, bottle caps, and other household materials floating throughout the Sargasso Sea, a region in the middle of the North Atlantic extending south and east of Bermuda.

Some areas may contain up to 500,000 pieces of plastic per square kilometer, said scientists from SEA, based in Woods Hole. Such a concentration, the researchers said, would rival that of the Great Pacific Garbage Patch in the Pacific Ocean, whose alarming sighting last year highlighted the extent of oceanic pollution and its potential impact on aquatic life.

Most of the Atlantic debris is believed to come from land thousands of miles away. Kara Lavender Law, SEA’s principal investigator, said waste, including materials put in recycling bins, can end up in rivers that flow into the ocean.

“How on earth have we done this to the ocean so far away from where most people are living?’’ Law asked yesterday. “You see objects float by, and you feel like there must be another boat nearby that has dumped all this stuff into the water, but there isn’t. It comes from land.’’

Materials caught in the Sargasso Sea are not likely to make their way back to the East Coast any time soon, Law said, but plastic pollution is still very much a coastal problem.

The only things that reached the SEA team — some 2,500 miles from the US coast — were materials that floated. Other items, such as the plastic used in most disposable water bottles, are too dense to be carried far. Instead, the material probably sank to the ocean floor.

“Only 3 to 5 percent of most plastics actually get recycled,’’ Giora Proskurowski, SEA’s chief scientist, said by phone yesterday from the SSV Corwith Cramer in Bermuda. “It’s not an answer. All those plastic sources we use: one-time water bottles, food packages, individually wrapped apple slices, or other ridiculous things, tiny, tiny fragments of each are ending up in the ocean.’’

Land dwellers may not be immune from the plastic, either.

Although densely concentrated in certain regions, the plastic particles are small, and in some cases, microscopic.

Their size makes the particles, which are not biodegradable and may contain poisonous chemicals, easy for marine animals to ingest. Some creatures can die from the exposure, said Dennis Nixon, associate dean at the University of Rhode Island’s Graduate School of Oceanography.

Some scientists suspect chemicals ingested from the plastic may travel up the food chain and could eventually harm humans.

“This could severely impact the food web,’’ Nixon said.

The 33-person crew, made up of 19 volunteers, set out in June, hoping that traveling more than 2,000 miles east of Bermuda would help them pinpoint the size and magnitude of the Atlantic patch of pollution.

To determine the plastic concentration in parts of the Atlantic, the crew towed a 1 meter-wide mesh net alongside the boat for about 30 minutes at a time. The net was examined, and every piece of plastic found was logged, picked off the mesh, and stored on the vessel. Like the debris in the Pacific, it is pulled together by gyres, rotating ocean currents that trap the garbage.

After more than a month at sea, the team will end its research today but without many answers.

“We know there are certain implications: entanglement, sea birds and mammals ingesting the plastic, providing a vehicle that could transport foreign species that could potentially wreck havoc in various ecosystems,’’ Proskurowski said.

“But what we don’t know is what happens when they degrade,’’ he said. “Do plankton eat them? Do they accumulate up the food chain? We don’t have answers to that, and that’s even scarier than knowing what we do know.’’

Wendy Kordesch, 25, a volunteer on the expedition, said the research had transformed her thinking on ocean pollution.

“There’s no floating refrigerators, no garbage islands, but there is a shocking amount of plastic,’’ said Kordesch, an oceanography graduate student from University of California, Santa Cruz. “We were farther away from land than I’ve probably ever been, and in every single tow there are small pieces of plastic that came up. It’s terrible.’’

Marissa Lang can be reached at mlang@globe.com.

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