Short communicationMicroplastic pollution in deep-sea sediments
Introduction
The world's seas and oceans are subjected to different kinds of threats of which the accumulation of anthropogenic debris is a major and worldwide problem that has been an environmental concern for decades. Despite the increased international attention, the build-up of these materials in the environment is considered problematic due to the increasing global plastic production (280 million tons y−1 in 2011 (PlasticsEurope, 2012)) and the continuing improper disposal of plastic waste. In the last decade it has been demonstrated that in the marine environment such large plastic items will break up into smaller fragments (Andrady, 2011, Cole et al., 2011) with dimensions as small as a few micrometre, the so called microplastics. Moreover, additional sources of microplastics have been identified: microplastic particles present in cosmetics (Fendall and Sewell, 2009) and microplastic fibres from fabrics such as polyester and polyamide (Browne et al., 2011, Dubaish and Liebezeit, 2013) present in domestic wastewater are not retained during sewage treatment and can thus enter the marine environment.
Many authors have defined microplastics as particles smaller than 5 mm (Arthur et al., 2009), while others have set the upper size limit at 1 mm (Claessens et al., 2011). While the value of 5 mm is more commonly used, 1 mm is a more intuitive value (i.e. ‘micro’ refers to the micrometre range). Most plastic present in the marine environment fits these small size classes. For instance, plastic particles <1 mm accounted for 65% of all marine debris items collected on beaches in the Tamar Estuary (U.K.) (Browne et al., 2010). Because of these small dimensions, microplastics become available for ingestion by organisms commonly not affected by the larger marine debris. Short-term laboratory trails have shown that marine invertebrates, representing different feeding strategies, can ingest these microscopic plastic particles. Polychaetes, bivalves, echinoderms and copepods will all, in at least one life stage, take up microplastics from the environment (Cole et al., 2013, Graham and Thompson, 2009, Thompson et al., 2004, Ward and Shumway, 2004). Once ingested, these microplastics can either be eliminated through defecation or retained in the tissues of the exposed animals (called translocation) (Browne et al., 2008, von Moos et al., 2012). Since there is a data gap concerning chronic effects of microplastic exposure, the implications of microplastic contamination in the marine environment are, to date, unknown.
Microplastics have been reported in the water column and marine sediments worldwide (Claessens et al., 2011, Law et al., 2010, Moore et al., 2001, Thompson et al., 2004), from low, background concentrations of 3 particles m−3 in water (Doyle et al., 2011) and 8 particles kg−1 in sediment (Thompson et al., 2004), to very high, hot-spot concentrations of 102 000 particles m−3 in water (Norén and Naustvoll, 2010) and 621 000 particles kg−1 in sediments (Liebezeit and Dubaish, 2012). The observed sediment concentrations all originate from sites located on the continental shelf. However, accumulation zones of floating plastic debris and associated microplastics, the so-called garbage patches, are located far from any continental margin. Hence, the question arises whether the degradation products of larger marine debris are present in deep-sea sediments as well, since surface particulate material can be rapidly exported to abyssal depths.
Here, we investigate the presence of microplastics in one of the most pristine of marine environments: the deep sea. To explore the hypothesis that microplastics have entered the deep sea, sediment samples from deep-sea locations worldwide were analysed for the presence of microplastics by means of a new and highly efficient extraction technique using a high density salt solution.
Section snippets
Materials & methods
Microplastic extractions were performed on 11 sediments samples originating from several locations in the Atlantic Ocean and Mediterranean Sea ranging in depth from 1176 to 4844 m (see Table 1). These deep sea systems represent different marine environments. The three sampling stations in the Atlantic sector of the Southern Ocean, off the polar front were representative for a pristine environment, since the sea floor of this remote location is still largely unexplored and assumed void of
Results & discussion
In three of the four locations studied, microplastics were recovered from the top 1 cm of the sediment samples (see Fig. 1). In total, five particles were identified as possible microplastics: 1 particle originating from the Nile Deep Sea Fan, 1 from the Southern ocean, and three particles from the Porcupine Abyssal Plain. No particles were recovered from the Congo Canyon. Based on the (limited) surface sampled it can tentatively be concluded that in/on the sea floor of the deep sea,
Acknowledgements
We thank crew and principal scientists of the following scientific cruises: RRS Discovery 229, Merian MSM13/3, Polarstern ANT-XXVIII/3 and Pourquoi pas? ROV Victor 6000 WACS cruise. We also thank Professor Strijckmans and his scientific team for access to and help with the micro-Raman spectroscopy and Professor Cnudde and Wesley De Boever for making the SEM-images.
Lisbeth Van Cauwenberghe is the recipient of a Ph.D. grant of the Agency for Innovation by Science and Technology (IWT, Belgium).
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