From the BBC News

Dr Richard Thompson at the University of Plymouth researches what happens when plastic breaks down (degrades) in seawater

They have identified plastic particles of around 20 microns – thinner than the diameter of a human hair.
In 2004 their study reported the incidence of the particles had been increasing over the years.

They have found plastic particles smaller than grains of sand.

They estimate there are 300,000 items of plastic per sq km of sea surface, and 100,000 per sq km of seabed.

Thompson and his team conducted experiments on three species of filter feeders and found that the barnacle, the lugworm and the common amphipod or sand-hopper all  readily ingested plastic as they fed along the seabed.

They wanted to  establish if chemicals can leach out of degraded plastic and if plastic absorbs other contaminants such as PCBs and other polymer additives.

“The plastics industry’s response is that much of the research is speculative at this stage, and that there is very little evidence that this transfer of chemicals is taking place in the wild.It says it is doing its bit by replacing toxic materials used as stabilisers and flame retardants with less harmful substances.
Whatever the findings eventually show, there is little that can be done now to deal with the vast quantities of plastic already in our oceans. It will be there for decades to come.”

You can read more about the problems of micro plastic pollution here.

More Science

And if you want more data on the problem here are just a few of the hundreds of studies being done. Thanks to Fabiano of www.globalgarbage.org for keeping us well informed.

Jan Zalasiewicz, Colin N. Waters, Juliana Ivar do Sul, Patricia L. Corcoran, Anthony D. Barnosky, Alejandro Cearreta, Matt Edgeworth, Agnieszka Gałuszka, Catherine Jeandel, Reinhold Leinfelder, J.R. McNeill, Will Steffen, Colin Summerhayes, Michael Wagreich, Mark Williams, Alexander P. Wolfe, Yasmin Yonan, The geological cycle of plastics and their use as a stratigraphic indicator of the Anthropocene, Anthropocene, Available online 18 January 2016, ISSN 2213-3054, http://dx.doi.org/10.1016/j.ancene.2016.01.002.
(http://www.sciencedirect.com/science/article/pii/S2213305416300029)
Abstract: The rise of plastics since the mid-20th century, both as a material element of modern life and as a growing environmental pollutant, has been widely described. Their distribution in both the terrestrial and marine realms suggests that they are a key geological indicator of the Anthropocene, as a distinctive stratal component. Most immediately evident in terrestrial deposits, they are clearly becoming widespread in marine sedimentary deposits in both shallow- and deep-water settings. They are abundant and widespread as macroscopic fragments and virtually ubiquitous as microplastic particles; these are dispersed by both physical and biological processes, not least via the food chain and the ‘faecal express’ route from surface to sea floor. Plastics are already widely dispersed in sedimentary deposits, and their amount seems likely to grow several-fold over the next few decades. They will continue to be input into the sedimentary cycle over coming millennia as temporary stores – landfill sites – are eroded. Plastics already enable fine time resolution within Anthropocene deposits via the development of their different types and via the artefacts (‘technofossils’) they are moulded into, and many of these may have long-term preservation potential when buried in strata.
Keywords: Anthropocene; Plastics; Stratigraphy

http://www.globalgarbage.org.br/mailinglist/S2213305416300029_In_Press_Accepted_Manuscript.pdf

Carme Alomar, Fernando Estarellas, Salud Deudero, Microplastics in the Mediterranean sea: Deposition in coastal shallow sediments, spatial variation and preferential grain size, Marine Environmental Research, Available online 18 January 2016, ISSN 0141-1136,http://dx.doi.org/10.1016/j.marenvres.2016.01.005.
(http://www.sciencedirect.com/science/article/pii/S0141113616300058)
Abstract: Marine litter loads in sea compartments are an emergent issue due to their ecological and biological consequences. This study addresses microplastic quantification and morphological description to test spatial differences along an anthropogenic gradient of coastal shallow sediments and further on to evaluate the preferential deposition of microplastics in a given sediment grain fraction. Sediments from Marine Protected Areas (MPAs) contained the highest concentrations of microplastics (MPs): up to 0.90±0.10 MPs/g suggesting the transfer of microplastics from source areas to endpoint areas. In addition, a high proportion of microplastic filaments were found close to populated areas whereas fragment type microplastics were more common in MPAs. There was no clear trend between sediment grain size and microplastic deposition in sediments, although microplastics were always present in two grain size fractions: 2mm>x>1mm and 1mm>x 0.5mm.
Keywords: Marine litter; MPAs; Anthropogenic gradient; Sieve fractions; Contamination; Balearic islands

http://www.globalgarbage.org.br/mailinglist/S0141113616300058_In_Press_Accepted_Manuscript.pdf

Teresa Rocha-Santos, Armando C. Duarte, A critical overview of the analytical approaches to the occurrence, the fate and the behavior of microplastics in the environment, TrAC Trends in Analytical Chemistry, Available online 11 December 2014, ISSN 0165-9936,http://dx.doi.org/10.1016/j.trac.2014.10.011.
(http://www.sciencedirect.com/science/article/pii/S0165993614002556)
Abstract: Plastics can be found in food packaging, shopping bags, and household items, such as toothbrushes and pens, and facial cleansers. Due to the high disposability and low recovery of discharged materials, plastics materials have become debris accumulating in the environment. Microplastics have a dimension <5 mm and possess physico-chemical properties (e.g., size, density, color and chemical composition) that are key contributors to their bioavailability to organisms. This review addresses the analytical approaches to characterization and quantification of microplastics in the environment and discusses recent studies on their occurrence, fate, and behavior. This critical overview includes a general assessment of sampling and sample handling, and compares methods for morphological and physical classification, and methodologies for chemical characterization and quantification of the microplastics. Finally, this review addresses the advantages and the disadvantages of these techniques, and comments on future applications and potential research interest within this field.
Keywords: Debris; Detection; Environment; Marine environment; Microplastic; Plastic; Sampling; Seawater; Sediment; Water

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http://www.frontiersin.org/Journal/10.3389/fmars.2014.00070/full

Reisser J, Proietti M, Shaw J and Pattiaratchi C (2014) Ingestion of plastics at sea: does debris size really matter? Front. Mar. Sci. 1:70. doi: 10.3389/fmars.2014.00070

Keywords: microplastics, marine debris, plastic ingestion, zooplankton grazing, copepods

http://journal.frontiersin.org/Journal/10.3389/fmars.2014.00070/pdf

http://www.biogeosciences-discuss.net/11/16207/2014/bgd-11-16207-2014.html

Reisser, J., Slat, B., Noble, K., du Plessis, K., Epp, M., Proietti, M., de Sonneville, J., Becker, T., and Pattiaratchi, C.: The vertical distribution of buoyant plastics at sea, Biogeosciences Discuss., 11, 16207-16226, doi:10.5194/bgd-11-16207-2014, 2014.

Abstract. Millimeter-sized plastics are numerically abundant and widespread across the world’s ocean surface. These buoyant macroscopic particles can be mixed within the upper water column due to turbulent transport. Models indicate that the largest decrease in their concentration occurs within the first few meters of water, where subsurface observations are very scarce. By using a new type of multi-level trawl at 12 sites within the North Atlantic accumulation zone, we measured concentrations and physical properties of plastics from the air–seawater interface to a depth of 5 m, at 0.5 m intervals. Our results show that plastic concentrations drop exponentially with water depth, but decay rates decrease with increasing Beaufort scale. Furthermore, smaller pieces presented lower rise velocities and were more susceptible to vertical transport. This resulted in higher depth decays of plastic mass concentration (mg m−3) than numerical concentration (pieces m−3). Further multi-level sampling of plastics will improve our ability to predict at-sea plastic load, size distribution, drifting pattern, and impact on marine species and habitats.

Review Status
This discussion paper is under review for the journal Biogeosciences (BG).

http://www.biogeosciences-discuss.net/11/16207/2014/bgd-11-16207-2014.pdf