A new study suggests more than five trillion pieces of plastic, weighing five times more than the Titanic, are floating in the world's oceans.

The study, published in the open-access, peer-reviewed journal PLOS ONE, estimates that 268,940 tons of plastic pollution are dispersed across the Earth's five oceans.

The vast majority of the plastic, some 92 per cent, is made up by what they call "microplastic," measuring less than five millimetres.

The paper's authors suggest birds, reptiles and marine mammals can get tangled in larger pieces of plastic. Furthermore, they suggest the breakup of already brittle microplastics pose a health risk all the way up the food chain as smaller organisms eat these particles and get eaten by larger predators.

The research, which is the first of its kind to study floating plastics of all sizes, was carried out over a six-year period from 2007 to 2013 in expeditions to the South Pacific, North Pacific, South Atlantic, Indian Ocean and waters surrounding Australia.

Scientists collected small plastic fragments using nets, while large pieces of debris from fishing-related equipment and your run-of-mill house household garbage consisting of buckets, bottles and plastic bags were observed from boats.

Because plastic is both durable and buoyant, the study found, particles have been spread throughout the world's oceans via currents. The plastic collects in ocean gyres -- massive vortexes of current – such as the "great Pacific garbage patch" in North Pacific Ocean, which is roughly the size of Texas.

The study stresses that its estimates are "highly conservative," and that it is difficult to account for the "potentially massive of amounts of plastic" also accumulating on shorelines, the ocean floor and inside marine life.