Researchers returned on 24 August from mapping and sampling a massive swirling cluster of rubbish floating in the middle of the Pacific Ocean, as the Dutch-borne crew works to refine a clean-up strategy it will roll out globally.

The crew of the Ocean Cleanup, backed by volunteers in sailboats, ventured to areas of the Great Pacific Garbage Patch, a swirling mass of human-linked debris spanning hundreds of miles of open sea.

The debris, concentrated by circular, clockwise ocean currents within an oblong-shaped "convergence zone", lies near the Hawaiian Islands, about midway between Japan and the US West Coast. The rubbish ranges from microscopic pieces of plastic to large chunks.

Oceanographer Julia Reisser said the group, working for about a month, collected samples as small as a grain of sand and as large as discarded fishing nets weighing more than 2,000lbs. They mapped the area, using aerial balloons and trawling equipment to locate samples.

The reconnaissance trip is the brainchild of Ocean Cleanup's 21-year-old founder, Boyan Slat, and backed financially by's chief executive Marc Benioff, among other philanthropic and crowdsourcing initiatives which brought in some $2.2m, according to Ocean Cleanup.

"Every week the volume of about 2 Empire State Buildings worth of plastic flows into the oceans where it damages ecosystems, it damages economy, and it also ends up in the food chain thereby potentially damaging us," said Boyan Slat.

The next phase, planned for 2016, is the deployment in Japanese coastal waters of a 2,000m scale model of the group's proposed debris collection system, which researchers believe could extend for 60 miles. That system will contain floating stationary booms tethered to the ocean floor and linked in a V shape intended to skim and concentrate surface plastics floating on top of ocean currents.

Slat, a Dutch inventor who gained attention as a teenager when he developed the floating boom system which uses technology used for anchoring deep sea oil rigs, said the project would be situated in international waters, away from shipping lanes.