Plastics are considered to be one of the major environmental challenges of our time. They are highly durable synthetic polymers, around 30% of which are produced for short-life purposes, such as disposable packaging, and are discarded within a year of being manufactured. Despite the large number of plastic items being manufactured and then thrown away, and visible evidence of plastic debris in ecosystems from pole to pole, environmental scientists for a long time struggled to find evidence of plastic accumulation (rather than presence) in natural ecosystems, until they began to examine microplastic particles (tiny plastic fragments, generally formed from the break-down of larger items) in sediments and ocean waters, where a steady build-up of plastics over time has been confirmed. However even these studies have failed to account for the amount of plastic thought likely to be present in the environment, leading scientists to suspect that a large amount of plastic is present but unaccounted for somewhere in the natural environment.
In a paper published in the journal Royal Society Open Science on 17 December 2014, Lucy Woodall of the Department of Life Sciences at The Natural History Museum, Anna Sanchez-Vidal and Miquel Canals of the Departament d’ Estratigrafia, Paleontologia i Geociències Marines at the Universitat de Barcelona, Gordon Paterson, also of the Department of Life Sciences at The Natural History Museum, Rachel Coppock and Victoria Sleight of the Marine Biology and Ecology Research Centre at Plymouth University, Antonio Calafat, also of the Departament d’ Estratigrafia, Paleontologia i Geociències Marines at the Universitat de Barcelona, Alex Rogers of the Department of Zoology at the University of Oxford, Bhavani Narayanaswamy of the Scottish Association for Marine Science and Richard Thompson, again of the Marine Biology and Ecology Research Centre at Plymouth University, discus the presence of microplastic particles in deep-marine sediment samples collected from a series of sites in the North Atlantic, Mediterranean and southern Indian Ocean.
The samples examined were taken from the upper portions of cores gathered for other studies by the Universitat de Barcelona and the Natural History Museum over a twelve year period. Because of this the samples were gathered following different procedures, limiting the amount of comparison that can be made between the samples. Nevertheless it was possible to establish the presence of plastics in areas not previously sampled, and compare the proportions of different plastics within individual samples.
Locations of sampling sites of bottom sediment and deep-water coral where content of microplasticswas investigated. Sample depth ranged down to 3500 m, for details see table 1. Sediment was collected by the University of Barcelona (circles) and the Natural History Museum (filled squares), and deep-water corals were collected by the Natural History Museum (open squares). Bathymetry corresponds to ETOPO1Global Relief Model. Woodall et al. (2014).
The areas sampled included open slopes in the subpolar North Atlantic, the northeast Atlantic and the Mediterranean, canyons in the northeast Atlantic and Mediterranean, basins in the Mediterranean and Corals from seamounts in the southwest Indian Ocean.
All of the samples were found to contain microplastics in the form of fibres 2-3 mm in length and ~0.1 mm in width. The most abundant fibre was rayon, which is not strictly speaking a plastic (it is made from dissolved and resolidified cellulose from wood-pulp, rather than hydrocarbons) and which comprised 56.9% of all the fibres found in the study; this is comparable to results for rayon in previous studies of synthetic fibres ingested by Fish (where 57.8% of all fibres were rayon) and in ice cores (where 54% of all fibres were rayon). Of actual plastics sampled 53.4% were polyester, 34.1% were 'other plastics (including polyamides and acetate) and 12.4% were acrylic.
Plastics were found at comparable levels to those seen in intertidal and shallow-marine sediments, and at a rate roughly a thousand times higher than found in surface waters. Given the vast areas covered by the deep ocean floor, this is likely to account for a substantial proportion of the 'missing' plastic predicted to be present in the natural environment.
All of the plastics found were heavier than water. At first sight this is what would be expected as such plastics should sink whereas plastics lighter than water should not, however for microplastics the situation is more complex, as such plastics will tend to be held at the surface by surface-tension, only sinking after becoming colonized by marine organisms, adhered to phytoplankton and the aggregated with organic debris and small particles in the form of marine snow.
The impact of microplastics on deep-sea ecosystems is unclear. In surface and shallow-marine organisms such plastics have been shown to have adverse effects both due to their physical and toxicological properties, and this is likely to be the case also with deep-marine organisms, but this cannot be asserted confidently without further study.
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