Microplastic pollution identified in deep-sea water and ingested by benthic invertebrates in the Rockall Trough, North Atlantic Ocean☆
Graphical abstract
Introduction
Plastic debris is a pervasive anthropogenic contaminant found extensively in the aquatic environment worldwide (Cozar et al., 2014, Hammer et al., 2012). As a major source of marine pollution, plastic debris meets ocean health index criteria and has been recognized as a global threat, joining other marine stressors such as climate change, ocean acidification, overfishing and habitat destruction (Amaral-Zettler et al., 2015, Halpern et al., 2012). The majority of plastic items manufactured have single-use application (Thompson et al., 2009) and between 4.8 × 109 to 12.7 × 109 kg of plastic is estimated to have entered the ocean in 2010 alone (Jambeck et al., 2015); by contrast an estimated 2.7 × 108 kg is afloat in surface waters (Eriksen et al., 2014). The progressive fragmentation of plastic objects into ever smaller and more numerous pieces should lead to the gradual increase of microplastics quantities (Andrady, 2011, Cozar et al., 2014, ter Halle et al., 2016), however global budgeting identifies major discrepancies between the abundance of plastics in surface waters, especially when considering microplastic particles (Cozar et al., 2014, Eriksen et al., 2014).
Microplastics, defined here as particles 1 μm - 5 mm in diameter (Arthur et al., 2009) are of particular environmental concern as they are a similar size to prey items and sediment grains and are therefore bioavailable to a wide diversity of organisms. Ingestion is reported in numerous species with documented impacts ranging from lethal to sub-lethal (Browne et al., 2008, Cole et al., 2015, Murray and Cowie, 2011, Welden and Cowie, 2016, Wright et al., 2013a), and trophic transfer of microplastics has been observed (Farrell and Nelson, 2013, Setälä et al., 2014). Additionally, small particles have been shown to translocate within the bodies of crabs and mussels (Browne et al., 2008, Farrell and Nelson, 2013), consequently microplastics potentially have a greater toxicological effect than larger plastic items. The high surface area to volume ratio means small particles have a greater area over which to absorb environmental contaminants; these may accumulate in the plastic, however the effect of plastic co-contaminants on biota is not yet clear (Koelmans, 2015).
The long-term fate and ‘lifecycle’ of microplastics in the marine environment is poorly understood. Distribution is influenced by abiotic (ocean currents, physical shearing, fragmentation and natural sinking (GESAMP, 2015)) and biotic factors (such as fouling (Fazey and Ryan, 2016), consumption and incorporation in faecal material (Cole et al., 2016) and settling detritus (Long et al., 2015)). These provide vertical transport pathways for microplastics from the sea surface to the benthos, thus it is hypothesized that microplastics are sequestered in the deep sea. There is a severe paucity of knowledge regarding microplastic pollution in the deep sea; however within the last few years microplastics have been documented in deep-sea sediments in regions of the Mediterranean Sea and the Atlantic, Pacific and Indian Oceans (Fischer et al., 2015, Van Cauwenberghe et al., 2013, Woodall et al., 2014), and more recently isolated from deep-sea benthic invertebrates (Taylor et al., 2016).
This study aims to provide a thorough assessment and quantification of microplastic ingestion by deep-sea benthic invertebrates displaying different feeding modes and presents the first quantification of microplastic pollution in deep-sea water. To test the hypothesis that microplastics are present at a deep-sea site in the Rockall Trough, Northeast Atlantic Ocean, benthic fauna and water samples were collected from a depth >2200 m. Samples were analysed to i) determine whether microplastics occur in this remote deep-sea location and ii) characterise and quantify the microplastics present.
Section snippets
Sampling location
The Rockall Trough is situated to the west of Scotland, UK. The monitoring site, 'Gage Station M’, is located in the Rockall Trough (57.300°N, −10.383°W) near the foot of Anton Dohrn seamount at a depth of 2200 m (Fig. 1). During the 2016 research cruise DY052 aboard R.R.S. Discovery, four epibenthic sled tows and one Conductivity, Temperature, Depth (CTD) cast for deep-sea water were undertaken.
On-board quality assurance/quality control (QA/QC)
QA/QC procedures were designed and employed at all stages to reduce the potential for sample
QA/QC
No microplastics were identified on the filters fitted to the ships water supply. When analysed with ATR-FTIR spectroscopy none of the potential contaminants sampled from the ship (ropes, filters, clothing) or laboratory (sterile consumable packaging, clothing) had spectra which matched that of material found in deep water or invertebrates samples. Laboratory controls yielded similar results; of the 5 fibres found on the atmospheric controls all were identified as cellulose. The number of
Discussion
The presence of microplastics in deep-sea water and the benthic invertebrate community is clearly demonstrated here, providing further evidence for the widespread distribution of anthropogenic microplastics in the marine environment. Microplastics are heterogeneously distributed in surface waters with concentrations ranging between 0.02 and > 100 particles m−3 in the Northeast Atlantic Ocean (reviewed in Lusher, 2015). The present study provides the first quantification of microplastic
Conclusion
This study demonstrates the presence of microplastics in deep-sea benthic fauna and water in the Rockall Trough. Further sampling of water and fauna, along with the addition of sediment cores are necessary to assess ecosystem-wide microplastic pollution in this region and monitor temporal changes. While this study focuses on the Northeast Atlantic Ocean, we hypothesize that microplastics are present throughout the global deep-sea. Further attention and sampling efforts should be directed to the
Funding sources
We are grateful for NERC National Capability funding grant R8-H12-85, for supporting the Extended Ellett Line cruises and SFG; a NERC Services and Facilities capital equipment scheme grant to the NERC National Facility for Scientific Diving for funding the software and hardware used to generate photogrammetry models. WCJ was jointly funded through a PhD scholarship awarded by the Scottish Association for Marine Science and the University of the Highlands and Islands.
Acknowledgments
Thanks are extended to Dr David Hughes and Martin Foley for assisting with deep-sea specimen collection, along with the captain and crew from RRS Discovery research cruise DY052 for enabling deep-sea operations. Dr. Ciaran Ewins for use of the ATR-FTIR and Fionn Murphy for contributing to the polymer reference FTIR spectra. Also, Rory MacKinnon for graphical abstract assistance.
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This paper has been recommended for acceptance by Eddy Y. Zeng.