A new estimate says that microplastic and macroplastic pollution could consist of as much as 269,000 tons floating in the world's oceans.

Though there has been no sufficient data to truly estimate the amount of plastic in the oceans, there has been no limit to guessing and speculation so Marcus Eriksen, from Five Gyres Institute, and colleagues set out to build a better model.

For their paper in PLOS ONE, they gathered data from 24 expeditions collected over a six-year period (2007-2013) across all five sub-tropical gyres, coastal Australia, Bay of Bengal, and the Mediterranean Sea.

Model results for global weight density in four size classes. Model prediction of global weight density (g km⁻²; see colorbar) for each of four size classes (0.33–1.00 mm, 1.01–4.75 mm, 4.76–200 mm, and >200 mm). The majority of global weight is from the largest size class. Credit: doi:10.1371/journal.pone.0111913.g003

The data included information about microplastics collected using nets and large plastic debris from visual surveys, which were then used to calibrate an ocean model of plastic distribution.

Based on the data and model, the authors of the study estimate a minimum of 5.25 trillion plastic particles weighing nearly 269,000 tons in the world's oceans. Large plastics appear to be abundant near coastlines, degrading into microplastics in the 5 subtropical gyres. The smallest microplastics were present in more remote regions, such as the subpolar gyres.

The distribution of the smallest microplastics in remote regions of the ocean may suggest that gyres act as 'shredders' of large plastic items into microplastics, after which they eject them across the ocean.

"Our findings show that the garbage patches in the middle of the five subtropical gyres are not the final resting places for the world's floating plastic trash. The endgame for micro-plastic is interactions with entire ocean ecosystems," says Marcus Eriksen, PhD, Director of Research for the 5 Gyres Institute.