Scientists who returned to the Bay Area this week after an expedition to the “Great Pacific Garbage Patch” brought piles of plastic debris they pulled out of the ocean — soda bottles, cracked patio chairs, Styrofoam chunks, old toys, discarded fishing floats and tangled nets.

But what alarmed them most, they said Tuesday, was the nearly inconceivable amount of tiny, confettilike pieces of broken plastic. They took hundreds of water samples between the Farallon Islands near San Francisco and the notorious garbage patch 1,000 miles west of California, and every one had tiny bits of plastic floating in it. And the closer they sailed to the garbage patch, which some researchers have estimated to be twice the size of Texas, the more plastic pieces per gallon they found.

“Marine debris is the new man-made epidemic. It’s that serious,” said Andrea Neal, principal investigator on the Kaisei, a 151-foot research ship on the trip.

Neal, a Santa Barbara researcher who has a doctorate in molecular genetics and biochemistry, said crews on the three-week voyage discovered tiny jellyfish eating bits of the plastic debris. The jellyfish are, in turn, eaten by fish like salmon or tuna, which people eat.

Because the plastic pieces contain toxic chemicals — and are believed to be able to absorb now-banned chemicals such as DDT and PCBs, which can persist in the environment for decades — state toxicologists have taken hundreds of the objects, along with more than 300 fish, to an environmental chemistry lab in Berkeley to see if any chemicals are moving up the food chain.

“Every day, every night, we’d pull up samples and pour the water through a sieve. It would be completely clogged with tiny pieces of plastic,” said Margy Gassel, a research scientist with the California Environmental Protection Agency. “It was so disturbing.”

The research was the most extensive look yet at the garbage patch, a collection of mostly plastic debris located 1,000 miles north of Hawaii. The bobbing debris field, where currents swirl everything from discarded fishing line to plastic bottles into one soupy mess, was discovered in the mid-1990s.

Not much is known about it, including when it began forming or even its exact boundaries. It cannot be seen from the air or from satellites because most of the plastic has broken down into billions of tiny, confettilike pieces that float just below the surface.

Scientists believe the trash washes down storm drains and rivers from places such as the Bay Area or Japan, eventually drifting into several large ocean vortices where currents swirl together.

Two ships embarked a month ago to study the site. The New Horizon, a 170-foot vessel, was sent by the Scripps Institution of Oceanography at the University of California-San Diego. The Kaisei — whose name means “ocean planet” in Japanese — left from Richmond. It was sent by Ocean Voyages Institute, a Sausalito nonprofit that privately raised $500,000 for the voyage.

Both ships met at sea, collected water samples and took thousands of readings and photographs. Their goal: to study the patch’s size, how the plastic affects wildlife and whether it may be possible to one day clean up some of it.

Doug Woodring, a former Merrill Lynch financier and one of the founders of Project Kaisei, said Tuesday at a San Francisco news conference that one solution to the problem might be to dramatically increase the use of plant-based, biodegradable plastic and to beef up plastics-recycling programs. Designing storm drains to catch plastic debris also is a possibility, he said.

“We’re not talking about a plastic-bag tax,” he said. “We need to move the needle beyond that.”

The garbage patch is emerging as a major international environmental concern. Not only do its plastics pose a potential chemical threat, but birds, sea turtles and other marine life die when they eat or become entangled in floating plastic. Invasive species such as crabs, barnacles and other marine life also can attach themselves to it and float across the globe.

In the central Pacific, there are up to six pounds of marine litter for every pound of plankton, according to a 2006 report from the United Nations Environment Programme. And roughly 46,000 pieces of plastic litter are floating on every square mile of the oceans there, the report found.

John Chen, a spokesman for the Bureau of International Recycling, an industry group that contributed to the trip’s costs, cited fees placed on bottles and new computers under California laws that help cover recycling costs. He said such fees may be a model for recycling all plastic products.

Research papers from the expedition will not be published for several months. But Mary Crowley, a Sausalito resident who owns a yacht chartering company, Ocean Voyages, and who cofounded Project Kaisei, said time is of the essence.

“The floating pieces of plastic — large and small — are like a spreading cancer on the ocean,” she said. “It’s impossible for me to think of what the ocean might be like in another 30 years if we don’t change.”

Contact Paul Rogers at 408-920-5045.