How much microplastic floats around in the plastic soup?

In this article (A global inventory of small floating plastic debris), all known data about densities of microplastics at sea are combined into new estimates. This is about plastics as they are sampled with the usual research nets (mesh size of mostly 0.3mm). The bulk of items caught in these nets indeed belongs to the microplastics, defined as particles less than 5mm. Larger items are caught only rarely in these nets. Globally, the number of microplastic particles is now estimated at 15 to 51 trillion pieces, their combined mass at 93000 to 236000 metric tonnes. Although this new estimate is somewhat higher than earlier ones, the calculated total represents only about 1% of the mass of plastic debris that is estimated to annually enter the world’s oceans, and which is thought to degrade to microplastic! Huge amounts of plastics are thus ‘lost’ in our oceans, a thought maybe more disturbing than the known plastic soup itself!

Publication

Van Sebille, E., Wilcox, C., Lebreton, L., Maximenko, N., Hardesty, B.D., Van Franeker, J.A., Eriksen, M., Siegel, D., Galgani, F. & Law, K.L. (2015). A global inventory of small floating plastic debris. Environmental Research Letters 10: 124006 (11pp). http://dx.doi.org/10.1088/1748-9326/10/12/124006