Session Chairs: Tracy Mincer, Woods Hole Oceanographic Institution; Linda Amaral-Zettler, Utrech University

 This session looks at the plastic marine debris budget, news media, and the general public to determine the best path forward.

Plastics have become the most common form of marine debris in the 60 years since they have entered the consumer arena and present a major and growing pollution concern. As materials of immense utility and durability, plastics represent a growth industry, with the current annual global production exceeding the total human biomass on our planet. Unfortunately, mismanagement of plastic waste is commonplace. It is estimated that nearly a third of single-use plastics escape the waste stream, creating the most common mechanism for the creation of plastic marine debris (PMD) in coastal regions. Once these predominantly buoyant plastic materials enter the ocean they can migrate large distances. For example, PMD from U. S. Northeastern Seaboard locations can migrate over 1000 kilometers to the interior of the North Atlantic Subtropical Gyre (NASG), in less than 60 days. Surface net tow surveys by several research groups have quantified PMD in the NASG and North Pacific Subtropical Gyre. Additionally, PMD has been documented to accumulate in all five of the world’s subtropical gyres, coastal areas, and remote areas including the Marianas Trench, Arctic and Antarctic sea ice, and pristine tropical islands. Indeed, it is now apparent that all ocean habitats have the potential to be impacted by PMD. However, the overall risk of microplastics (commonly described as 5 millimeters to 1 micrometer in size) and nanoplastics (less than 1 micrometer in size) on biota such as filter feeding species is underexplored.

On average, it is estimated that 8 million metric tons of plastic escape the waste stream and enter our oceans annually. A recent model projected that over 150 million tons have been input to the oceans since plastic has entered the consumer arena. Paradoxically, the highest PMD estimate from recent global surface ocean surveys is only 250,000 metric tons– orders of magnitude lower than the amount of PMD projected, begging the question: “Where is all the plastic?” New technologies such as Raman Spectroscopy and micro-FTIR are allowing unprecedented detection of micro- and even nanoplastics. And methods separating micro- and nanoplastics from sediments and water column particulates such as ‘marine snow’ are yielding new insights into the distributions of PMD. Microbes have also been shown to interact with PMD, decreasing buoyancy, and possibly accelerating its degradation. These microbial consortia colonizing PMD can now be analyzed with powerful laser-scanning confocal visualization methods and combined with molecular probes, providing new insights into the spatial and temporal organization of biofilms on PMD. Computational models integrating datasets are yielding insight into the distribution of PMD below the ocean surface.

The overarching theme and goal of this session is to discuss integrative approaches of technologies, such as the ones listed above, to enable the collection of datasets to rigorously determine, the residence time, distribution, sources and sinks of PMD. We feel that this session will be well-received by the PMD research community and will provide a framework for future large-scale PMD budget estimations.




Micro-Plastic Particle Analysis of Hudson River Surface Water Using Novel Flow-Through Imaging Raman Spectroscopy

presenting: Scott Gallager (Woods Hole Oceanographic Institution, United States); authors: Scott Gallager (Woods Hole Oceanographic Institution, United States), Wade McGillis (Columbia University), John Lipscomb (Riverkeeper, Inc.)

It is estimated that an average of 5-13 million MT of single-use plastic products enter the world’s ocean each year, degrade through photochemical and mechanical abrasion, and become what is known as microplastics (MP)- particulate plastics between 1 µm and 5 mm. The fate of MPs is only starting to be revealed, but is fundamentally an oceanographic problem since their distribution is a function of both large and small scale mixing, microbial degradation, ingestion by a variety of suspension feeders, and nucleation of marine snow particulates, which export MPs to the deep sea. This study provides an overview of the development of a flow-through particle sensor based on both particle microscopic imaging and time-domain Raman spectroscopy with results of a cruise along the entire Hudson River sampling surface water continuously. Surface waters of the Hudson River contained 0 to 4.4 round, fiber, sliver, and bead particles/m3 of type PS, PE, PET, and PP, apparently higher in areas of maximum population density. Flow-through particle analysis using optics and Raman spectroscopy is possible, but the Raman signal to noise ratio must be maximized and fluorescence minimized using time-domain spectroscopy.


The Role of the “Plastisphere” Microbiome in Plastic Resin Density Changes Over Time

presenting: Linda Amaral-Zettler (NIOZ Royal Netherlands Institute for Sea Research and Utrecht University, Netherlands); authors: Linda Amaral-Zettler (NIOZ Royal Netherlands Institute for Sea Research and Utrecht University, Netherlands), Erik Zettler (NIOZ Royal Netherlands Institute for Sea Research and Utrecht University), Cathleen Schlundt (Marine Biological Laboratory), Drishti Kaul (J. Craig Venter Institute), Chris Dupont (J. Craig Venter Institute ,), Jessica Mark Welch (Marine Biological Laboratory), Tracy Mincer (Woods Hole Oceanographic Institution)

While macroplastic is the most conspicuous and iconic debris in the marine environment, micro (< 5 mm) and nano-sized (<50 µm) plastic particles are now recognized as a growing concern. The disconnect between a large and recurring source and a relatively small standing pool of Plastic Marine Debris points to large and unknown sinks that must account for the fate of the “missing plastic”. Plastic is colonized within hours of contact with water by a thin film of microorganisms, what we refer to as the “Plastisphere” microbiome. Important questions include how does the density of plastic in the ocean change over time as a result of biofilm formation, and how this determines whether the plastic sinks. As part of our ongoing research on microbial interactions with plastic marine debris, we conducted a long-term incubation experiment in temperate marine waters off Woods Hole, MA employing polyethylene (PE), polypropylene (PP), and expanded polystyrene resins to look at how biofilms begin, grow and change by collecting samples weekly for a month, then monthly for a year. In addition to monitoring changes in density of colonized resins, we employ a multiphasic approach including next-generation amplicon and metagenomics sequencing, culturing, Scanning Electron Microscopy, and most recently Combinatorial Labelling and Spectral Imaging – Fluorescence In Situ Hybridization (CLASI-FISH). Time series investigations such as these, provide a time-stamp on the succession and community assembly in Plastisphere communities that is difficult if not impossible to achieve in naturally collected samples and allow us to interrogate the importance of the spatial structure of the Plastisphere.


The terminal rising velocity of ocean plastic

presenting: Francesco Federico Ferrari (The Ocean Cleanup, Netherlands); authors: Francesco Federico Ferrari (The Ocean Cleanup, Netherlands), Laurent Lebreton (The Ocean Cleanup), Anna Schwarz (The Ocean Cleanup), Hannah Maral (The Ocean Cleanup), Julia Reisser (The Ocean Cleanup)

Buoyant plastics are now ubiquitous in the world’s ocean. They are comonly sampled with surface neuston nets that only sample the first centimeters of the water column. As wind-induced vertical mixing can lead to the distribution of buoyant plastics throughout the water column, a substantial fraction of ocean plastics can be missed by sea surface samplers, potentially leading to underestimations of plastic pollution levels. A linear model formulation has been proposed to correct sampled concentration for this effect, which is a function of sea state and ocean plastics’ terminal rising velocity (Wb). The latter refers to a constant speed driven by the buoyancy of the particle and friction forces in an undisturbed water column. In this study, we measured the Wb for 764 plastic pieces collected in the North Pacific Ocean. The plastics length ranged from 0.5mm up to 2.5m, and they were classified into four different types: hard plastic, ropes/nets/lines, pellets and foam. Using containers filled with seawater, we measured the Wb of each ocean plastic particle 3 times. Our results show that ocean plastics’ Wb varies within three orders of magnitude, with hard plastics Wb varying between 1.31 and 9.10 cm sˉ¹; ropes/nets/lines between 0.47 and 7.43 cm sˉ¹, pellets between 3.96 and 6.58 cm sˉ¹; and foam between 0.97 and 23.95 cm sˉ¹. Wb was also influenced by the size of the plastic debris, with this speed increasing proportionally to the ocean plastics’ length. Our measurements were used to develop a series of conversion matrices that determine ‘depth-integrated’ concentrations from in-situ surface samples as a function of observed sea state (Beaufort scale) and plastics’ type and sizes.


Plastics in Antarctica – preliminary findings from the Antarctic Circumnavigation Expedition (ACE)

presenting: Peter Ryan (FitzPatrick Institute of African Ornithology, South Africa); authors: Peter Ryan (FitzPatrick Institute of African Ornithology, South Africa), Giuseppe Suaria (CNR-ISMAR), Vonica Perold (FitzPatrick Institute of African Ornithology), Jasmine Lee (Centre for Biodiversity Conservation Science), Stefano Aliani (CNR-ISMAR (Institute of Marine Sciences – Italian Research Council))

The Antarctic Circumnavigation Expedition (ACE) sampled micro, meso and macroplastic litter around Antarctica from December 2016 to March 2017. Only small numbers of microfibres were found in beach sediments from sub-Antarctic and Antarctic sites, and surface tows with a 200 micron neuston nets captured no mesoplastic items. Only 22 macrolitter items were observed south of the Subtropical Front in almost 15,000 km of transect counts, confirming that the Southern Ocean is the ocean least polluted by plastics globally. However, macro debris was found in two of the small number of seabed trawls, and apparently synthetic microfibres were detected in virtually all bulk water samples collected around Antarctica. Surprisingly, there was no marked gradient in these fibres as we approached continental source areas. Confirmation of the identity of these fibres is still pending, but if they prove to be plastic, they suggest that all the world’s surface waters apparently carry low concentrations of microfibre pollutants, at a density of ~0.1-1 fibres per litre.


Microplastic screening and plastic surface weathering characterization with optical microscopy and SEM/EDS

presenting: Zhong-Min Wang (Environmental Health Laboratory, United States); authors: Zhong-Min Wang (Environmental Health Laboratory, United States), Jeff Wanger (Environemtal Health Laboratory), Sutapa Ghosal (Environmental Health Laboratory), Stephen Wall (Environmental Health Laboratory)

This study aimed to 1) develop and optimize a rapid procedure for microplastic screening with optical microscopy and scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM/EDS) suitable for fish guts and water samples, and 2) characterize plastic surface weathering using SEM/EDS. Microplastic particles from Atlantic and Pacific Ocean trawls, lab-fed fish guts, and ocean fish guts were characterized using both optical microscopy and SEM/EDS in terms of size, morphology, and chemistry. The analysis procedure is summarized as a flowchart as a practical reference for future studies. Optical microscopy yielded morphological classifications and size ranges of particles or fibers present in the sample, and also helped identify candidate plastic particles. SEM/EDS analysis was used to rule out non-plastic particles and further screen samples for potential microplastic, based on their elemental signatures and surface characteristics. Likely chlorinated plastics such as polyvinyl chloride (PVC) were identified with SEM/EDS due to their unique, elemental chlorine signatures, as were mineral species, often falsely identified as plastics by optical microscopy. Particle morphology determined by optical microscopy and SEM suggests the ocean fish ingested particles contained both degradation fragments from larger plastic pieces and also manufactured microplastics. SEM/EDS revealed unique insights into plastic degradation, likely weathering mechanisms, and environmental fate via high resolution imaging of characteristic cracks on the plastic surface. The ocean fish and trawl SEM results were consistent with their known environmental exposures, and revealed pigment particles consistent with manufactured materials.


The Arctic deep sea – a sink for microplastic ?

presenting: Melanie Bergmann (Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Germany); authors: Melanie Bergmann (Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Germany), Vanessa Wirzberger, Mine B. Tekman, Thomas Krumpen, Claudia Lorenz, Sebastian Primpke, Gunnar Gerdts

Some 99 % of plastic debris projected to enter our oceans has not been captured by current global litter estimates based on empirical data. It has been speculated that a large fraction of plastic debris evades our detection through fragmentation into small particle sizes, uptake by biota and accumulation in remote environments such as the deep ocean floor, which covers 60 % of the Earth.

Here, we analysed nine sediment samples taken at the HAUSGARTEN observatory in the Arctic at 2,340 – 5,570 m depths by Attenuated Total Reflection FTIR and µFTIR spectroscopy. Our results indicate the widespread occurrence of high numbers of microplastics (MP) in Arctic deep-sea sediments (44 – 3,463 MP L-1). The northernmost two stations harboured the highest MP quantities, indicating the importance of sea ice. A positive correlation between MP and chlorophyll a suggests vertical export via incorporation in sinking (ice-) algal aggregates. Overall, 18 different polymer types were detected dominated by chlorinated polyethylene (38 %), polyamide (22 %) and polypropylene (16 %). Almost 80 % of the MPs were ≤ 25µm. Many previous studies did not capture this size, which may partly explain why the MP concentrations are amongst the highest recorded from benthic sediments so far. MP quantities on the seafloor are 2 – 3 magnitudes higher than at the sea surface (Tekman et al.) indicating that the deep Arctic seafloor is a major sink for MP. This highlights the need to incorporate data from the deep sea into global litter estimates if we want to tackle the question ‘Where is all the plastic?’.