Doctoral Programme on Marine Ecosystem Health and Conservation
 PhD Subject Catalogue Fifth Edition - 2014
Microplastic distribution and ecological interactions across latitudinal gradients
PhD Code: MARES_14_02:
  • Host institute 1: P4 - Galway Mayo Institute of Technology (GMIT)
  • Host institute 2: P7 - University of Plymouth
Research fields:
  • T2 - Understanding biodiversity effects on the functioning of marine ecosystems
  • Rick Officer
  • Richard Thompson
  • Ian O'Connor
Contact Person and email: Rick Officer -

Subject description
ABSTRACT: Marine microplastic pollution is of increasing concern worldwide. Many plastics are less dense than seawater and float in the sea surface micro-layer where they interact with plankton communities and their consumers. The ubiquitous nature of marine microplastic pollution means that their potential impacts on ecosystem functioning will not be limited to source areas. Whilst the extent of microplastic transport within the water column is not well understood, poleward transport in ocean currents has been postulated. This project aims to ascertain the distribution, abundance and transport of microplastics across latitudinal gradients. At different latitudes, the project will assess the fate of microplastics within trophic systems and the propensity for ecosystem functions to deal with this pollution.
The primary aim of the project is to:
  • Describe latitudinal gradients in the distribution of microplastics and sorbed chemical pollutants.
  • Our hypothesis is that both will be more abundant at high latitudes. The project will then aim to:
  • Identify reasons for the observed distribution patterns (potentially including poleward transport, and exclusion from thermohaline circulation), and,
  • Examine some implications arising from the observed distribution (e.g. increased interaction in polar food webs). 
SCIENTIFIC BACKGROUND: Contamination of the world’s open oceans, enclosed seas and coastal waters by synthetic non-biodegradable debris is increasing [1, 2]. Plastics compose 60-80% of the marine litter [3, 4] currently accumulating on the sea surface, the sea floor and shorelines worldwide. Whilst the impact of larger visible items of plastic has been well studied [5, 6], the importance of microplastics (<5mm particles) has emerged in research only within the last decade [7]. Microplastics enter the marine environment through the break down of larger plastics through mechanical and biological processes [8], or through direct input as abrasive scrubbers (from cosmetics) [9, 10, and 11], or as the raw granules, pellets and powders intended for use in the production of plastic products [12]. Once in the sea microplastics become suspended in the water column [13], in surface waters [14], and in sediments [15, 16]. Monitoring of the quantity and distribution of microplastic particles [20] in the surface waters indicates accumulation [17, 18, and 19]. Given that their removal from the environment is probably impossible it is important to ascertain the fate and impact of microplastic pollution within trophic systems, and on ecosystem functioning. This imperative is reflected in Europe within the Marine Strategy Framework Directive (2008/56/EC); the distribution and fate of plastics as marine pollutants falls within MSFD Descriptor 10.
The widespread distribution of microplastic pollution within the marine environment means that their impact on trophic systems and ecosystems will not be limited to their sources. Furthermore, the transport of microplastic pollution within oceanic current systems may exacerbate impacts at destinations of water movement. Whilst this issue has been well addressed within convergent zones and gyres [17, 18, and 19] there are currently no studies addressing the pole-ward transport of microplastics. Evaluating the relationship between source and sink redistribution of microplastics will help identify whether Polar regions may also be places for accumulation of microplastics [25]. Oceanic currents could act as transport vectors of pollutants to the Arctic [26]. The Arctic Ocean receives water from three main current systems;
  • the Bering Strait brings warm oceanic water from the Pacific (Bering Sea) to the Arctic Ocean (Chukchi Sea),
  • the North Atlantic Current runs between Spitsbergen and the Siberian coast, and,
  • the west Spitsbergen current (WSC) carries warm saline north Atlantic ocean waters via the Fram Strait to the inner Arctic (Norwegian Sea).
 The rapid cooling of such current systems through thermohaline circulation has a well understood effect on the redistribution of heat and salt, and an important regulatory effect on the Earth’s climate. Less understood is the interaction of these circulation systems on the distribution of microplastics suspended in seawater. This project will assess, through a mixture of at-sea monitoring and laboratory experimentation, the extent of pole-ward transport of microplastics and the propensity for microplastics to be retained in polar waters due to the exclusion in the density driven thermohaline circulation. Common plastic polymers such as polyethylene, polypropylene and polyamide have specific densities of 0.92-0.97, 0.9-0.91, and 1.01-1.05 g/ml respectively. Being less dense than sea water (~1.025g/ml) most polymers float in the sea surface micro layer. However, once fouled with organic material, microplastics can sink to deeper water and the benthos. It is unknown whether fouling might increase density to the extent that microplastic particles can become incorporated into the deep water formed through thermohaline circulation [24]. If so, then the pole-ward transport of microplastics will be mitigated by the continued transport of microplastics into the deep oceanic waters. It is more probable that suspended microplastics cannot overcome the density gradient and are therefore excluded from the thermohaline circulation and retained in Polar waters.
The probable retention of microplastics in Polar waters increases the likelihood of interaction of these pollutants within trophic systems. The second phase of the project considers whether the marine organisms interacting with microplastics can be used as biomarkers for marine litter pollution. 
There are currently no studies confirming the presence or absence of microplastics in polar environments and it is therefore vital to establish whether this form of marine pollution is present. In the first instance this project will contribute towards the MFSD requirement for a coordinated monitoring programme for marine litter. This research will therefore progress achievement of Good Environmental Status as required by 2020 under the MSFD.
Distribution and abundance of microplastic pollution across latitudinal gradients:
A newly established method for continuously sampling microplastics via ship’s underway seawater intake will be used to monitor plastic distribution and abundance. A hose is attached to the seawater intake and the pressure is set to achieve a known flow rate. The water is passed through a 250µm sieve for a known period. The sieve is covered to prevent any airborne contamination. After the allotted time, the sieve is replaced to allow for continuous monitoring. The particles collected in the sieve are re-suspended in filtered seawater and then passed under vacuum onto a 47mm GFC glass microfiber filter paper. The filter paper is then stored for subsequent analysis under microscope for the presence of microplastics. Sampling can be conducted 24 hours a day and requires minimum attention. The research can therefore utilise spare berths available on scheduled collaborative research surveys without impinging on the principal research focus, and without substantial cost. Access to oceanographic expertise and to the European research vessel fleet is available to the project through existing collaborations. Potential collaborations with some associate partners to MARES may also help overcome logistical challenges.
Propensity for transport in the Thermohaline circulation:
A laboratory experiment is proposed in the controlled temperature facilities at GMIT. Manipulation of the level of fouling and type of plastic will be used to examine the extent to which microplastics may be incorporated within, or excluded from, the thermohaline circulation.
Analysis of samples and identification of polymers:
Samples will be sorted using the Image Pro photographic analysis software available at GMIT. Items will be photographed, described and measured for maximum length, colour and shape (fragment, fibre, bead, film).
To identify the polymers samples will be subjected to Fourier Transform Infra-Red Spectrometry (FT-IR - Bruker IFS 66 Spectrometer and Hyperion 1000 microscope) at the University of Plymouth. FT-IR conducted on individual fragments, pellets and fibres of unknown polymers will determine the structure of molecules through analysis of their absorption spectra. Each sample is compressed to a minimum thickness using a diamond compression cell, to achieve maximum absorbance. Computer software, such as OPUS v5.5, produces output spectra that identify the chemical bonds within the sample molecules. Output spectra will then be compared to known spectra from the OPUS polymer database using Euclidian Distance: the spectral distance between known spectra and that of the debris being analysed are assessed (i.e. the smaller the distance, the closer the match to the reference spectra).
Ecosystem Functioning and Trophic Interactions:
The potential for microplastics to concentrate and transfer organic pollutants is of significant interest. Putative prey species represent a possible transfer pathway of plastics and their associated pollutants. In conjunction with the oceanographic sampling, organisms at a variety of trophic levels will be examined for the presence of microplastics and associated pollutant concentrations. In addition to prey species a variety of commercial fisheries operate along the latitudinal gradient, these species will also be examined for the presence of microplastics as a possible mechanism for the transfer of pollutants into the human or animal foodchain. When species and areas have been analysed this information will be used to generate an ecological risk assessment. This will link what is known about the spatial and temporal distribution of predators, with the results of the distribution and abundance of microplastic particles in water and sediments and in prey species.
  • [1] Environmental Research 108: 131–139, 2008.
  • [2] Philosophical Transactions of the Royal Society B. 364:2013–2025, 2009.
  • [3] Marine Debris -Sources, Impacts and Solutions. Springer, New York, pp. 56–66, 1997.
  • [4] Plastics in the Environment: Environment Agency, 2001.
  • [5] Marine Debris-Sources, Impacts and Solutions. Springer, New York, pp. 99–139, 1997.
  • [6] Marine Pollution Bulletin 44: 842–852, 2002.
  • [7] NOAA Technical Memorandum NOS-OR&R30, 2009.
  • [8] Plastics and the environment. John Wiley and Sons, England: 2009.
  • [9] Marine Pollution Bulletin 22: 41–42, 1991.
  • [10] Marine Pollution Bulletin 32: 867–871, 1996.
  • [11] Marine Pollution Bulletin 58: 1225–1228, 2009.
  • [12] Philosophical Transactions of the Royal Society B 364: 1973–1976, 2009.
  • [13] Marine Pollution Bulletin, 49: 291−294, 2004.
  • [14] Marine Pollution Bulletin 52: 761–767, 2006.
  • [15] Science 304(5672): 838, 2004.
  • [16] Environmental Science & Technology 45: 9175−9179, 2011.
  • [17] Marine Pollution Bulletin 28(1): 39–43, 1994
  • [18] Marine Environmental Research 71: 41–52, 2011.
  • [19] Biology Letters 8(5): 817–820, 2012.
  • [20] Interdisciplinary Studies on Environmental Chemistry 5: 251–259, 2011.
  • [21] Journal of Geophysical Research 101(C3): 6553-6576, 1996.
  • [22] Autonomous Underwater Vehicles (AUV) IEEE/OES, 2012.
  • [23] Polar Research 20(2): 177–184, 2001.
  • [24] Philosophical Transactions of the Royal Society B 364: 1999-2012, 2009.
  • [25] Marine Pollution Bulletin 62: 1589–1591, 2011.
  • [26] Marine Pollution Bulletin 60: 1810-1814, 2010.

Expected outcomes
This proposal will produce the following tangible outputs:
  • Three peer reviewed papers;
  • International collaboration between third level institutes: GMIT and University of Plymouth.
 This project will: 
  • Directly contribute to member states' requirements under the marine strategy framework directive and the OSPAR convention;  
  • Directly contribute to the evolving development of monitoring programmes and the development of indicators for microplastics within MSFD Descriptor 10;  
  • Develop the use of marine organisms as biomarkers for marine litter pollution - this will progress achievement of Good Environmental Status as required by 2020 under the MSFD;  
  • Provide data and interpretation to address OSPAR recommendations such as “Criteria for the Identification of Species and Habitats in need of Protection and their Method of Application” and “On the Protection and Conservation of the Ecosystems and Biological Diversity of the Maritime Area”.

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