Dr. Andrea Stolte


Plastics in the marine environment

Basstoelpel Gennets nesting on fishing net

Marine plastic contamination is one of the major environmental challenges of our time. With the increasing production of plastics and availability of modern goods to the remotest places on Earth, the influx of plastics into the marine environment must have been steeply increasing as well. While it is easy to transport consumer goods to remote locations, it takes much longer to build the infrastructure for waste management and even more so for plastic recycling. Landfills are still one of the most common ways to dispose of household waste, even in the most industrialised European, North American, and Asian countries. Although in Europe energy recovery by burning of plastics and recycling ratese are increasing, PlasticsEurope estimates that in the year 2012 38% of plastic waste was disposed of in landfills, amounting to 10 Million tonnes that entered the environment in Europe alone. Several European coastal countries, including the UK, depose of more than two thirds of their plastic waste in landfills (PlasticsEurope 2013, Figure 13). While landfill bans provide an efficient means to minimise plastic waste entry into the natural environment, increasing storm events and storm surges increase the probability that landfill waste enters rivers and the marine environment. From the total amount of 275 Million tonnes of plastic waste generated in 192 coastal countries worldwide in the year 2010, a recent study calculated that between 4.8 and 12.7 Million tonnes of plastic waste are likely to enter the world's oceans (Jambeck et al. 2015).

Over the past two decades, I followed the developments and news in ocean plastics and their imminent problems closely. One of my aims when studying environmental science and protection was to work on a more thorough quantification of the plastics problem and on scientific mitigation measures. When I was offered a Master thesis subject on microplastics in beach sediment, I seized the opportunity to start my first project in ocean plastics.

Microplastics in the World's Oceans

Green plastic particle (Markgrafenheide Beach) Green plastic particle (Markgrafenheide beach)

Under the influence of wave action, UV radiation from the Sun, and bacteria and small organisms, larger plastic pieces degrade into increasingly smaller fragments. In water, plastic materials leach chemical additives that were include to preserve their flexibility and protect them from UV radiation. With these additives leaching into the water, the polymer structure becomes brittle and more prone to mechanical and UV breakup. The longer the fragments are exposed to the natural elements, the smaller the particles become. When they reach sizes below 5 Millimeters, they are considered microplastics.

In the marine environment, microplastics have several adverse effects. They are consumed from the smallest to the largest filter-feeders, from crustaceans to mussels (e.g., von Moos et al. 2012, Cole et al. 2013, Thompson et al. 2004), and likely even by species as large as balean whales and sharks (Fossi et al. 2012, 2014).

Possible microplastic sphere (Boergerende Beach) Possible microplastic sphere (Boergerende Beach)

Leaching chemicals with endocrine-disrupting functions into the environment, they might have adverse effects to the reproductive capabilities of marine species, including the major fish stocks currently used to feed humans. Marine microplastics have already entered the human food chain. Investigating mussels produced for human consumption at the French Atlantic coast and in the German North Sea, Van Cauwenberghe & Janssen (2014) find about one microplastic particle is consumed for every 3 gramms of mussel flesh. As a consequence of the net and line structures emploid in aquaculture, mussels produced for human consumption show particularly rich synthetic fibre concentrations of more than 100 microfibres per mussel, as shown by Mathalon & Hill (2014). While mussels from aquacultures contain on average more microfibres in their intestinal tracts and tissue, the same authors also find large amounts of microfibres in the guts of mussels collected in the wild. These studies show that microplastics have already entered the human food web in addition to the marine ecosystem, even though comparatively few quantitative analyses on selected locations are available to understand the full extent of the problem of microplastic contamination in the Oceans.

Microplastics at the German Baltic Coast

The microplastic contamination in beach sediments had not been measured before in the Baltic proper or at the Baltic coasts. As one of our goals was to characterise the entry pathways for microplastics at the German Baltic coast, four sampling areas were tested. With locations along the Rostock coastline, the island of R\"ugen, and the Oder/Peene outlet into the Baltic Sea we covered touristic activity, city discharges, the Rostock/Warnow overseas harbour, and fishing harbour influences as possible sources for microplastics. For comparison, two locations at the North Sea Jade Bay were also sampled. As no spectroscopic identification was available for this project, microplastics were selected on the basis of their colour. We found concentrations of 0-7 coloured particles/kg dry sediment and 2-11 fibres/kg dry sediment in all samples. Using standard dissecting microscopes at 3-4 x magnification, discovered microplastic particles ranged from 55 Micrometer to 1 Millimeter in size. This means that in every yoghurt glass of sand collected at German beaches, a few plastic particles and fibres smaller than 1 Millimeter will be found. While this does not sound much, it has to be kept in mind that we were not able to distinguish discoloured, transparent or white/yellowish plastic particles and clear synthetic fibres from natural sediment. So these values are strict lower limits, and the true amount of microplastics might be substantially larger. Plastics are exposed to UV radiation and chemical leaching in the marine environment. The same effects that contribute to the degradation of macroplastics into smaller pieces also lead to discolouring or yellowing of plastic materials. Hence, it can be expected that most of the plastic items will become lightly coloured over time -- in the same way as can be observed when leaving plastics out in a sunny garden. This is even more expected for mircoplastics, as their surface area is particularly large and fragmented compared to their minute volume.

rostock_fibres rostock_particles
Coloured fibres in Rostock sediment samples.
The colours illustrate the observed range of microplastics colours. Up to 2 fibres were found in blind reference samples in the laboratory, concentrations above 2 fibres show the contamination in beach sediments. No samples were taken in April at Warnemuende beach.
Coloured particles in Rostock sediment samples.
While only a few particles per ~800 gramm sample were found, the number of transparent or lightly coloured microplastic particles in these natural sediments is presently unknown. Nevertheless, it is a surprisingly positive finding that several samples did not show any microplastic particle content. No samples were taken in April at Warnemuende beach.

The concentration of coloured microplastic particles and fibres was calculated after the rest sediment was dried. Overall, we find a particularly high concentration of synthetic particles and fibres at the Peene outlet, where the Oder estuary discharges into the Baltic Sea. It might seem likely that Oder effluent carries city and industrial discharge from Szeszin and other cities on the river banks, yet the beach at Kamminke inside the Stettiner Haff shows the lowest microplastic contamination of all sites, with only one coloured particle and no coloured fibres at all. The high concentrations of particles and fibres at Freest are therefore likely to originate from the Freest fishing harbour. Harbour locations at the Belgian and the Norwegian coast were previously shown to be highly microplastic-contaminated sites (Claessens et al. 2011, Noren 2008), in agreement with this suggestion. The second highest synthetic particle and fibre concentrations are found at Dangast beach in the North Sea Jade Bay. Here, the paper recycling plant located in the city of Varel in immediate neighbourhood to the Jade estuary was suggested as a major source of plastics contamination before (Dubaish & Liebezeit 2013).

Comparison between the Baltic Coast and the North Sea

Microplastic concentrations were measured at several locations on beaches at the North Sea Coast as well as in deeper waters of the continental and Helgoland shelfs. Below, the measurements from the Baltic and Jade Bay survey are compared to these other locations. Only studies using similar means to confirm particles as microplastics either by intense colouring (as was done here) or via spectroscopy are compared. The concentrations in studies using colouring as a tracer for synthetic, anthropogenic material must be considered lower limits, as transparent and naturally coloured particles could not be taken into account.

coloured microplastic concentrations coloured microplastic concentrations
Mean concentrations of coloured particles and coloured fibres per kg dry weight sediment. No coloured fibres were found at Kamminke beach. Comparison of microplastic concentrations at Baltic beaches and in the North Sea. All studies identify microplastics either on the basis of intense colours or via spectroscopy. Beach sediments were sampled at Norderney (Dekiff et al. 2014), Sylt (Lorenz 2014), and the Belgian coast (Claessens et al. 2011). Studies on the Belgian Continental Shelf, Belgian Harbours (Claessens et al. 2011), and the Helgoland Shelf (Lorenz 2014) report concentrations in sublitoral sediment.

In addition to industrial and harbour sites, we also find high fibre concentrations at Warnemuende beach in the peak of the tourist season in July 2014. In all other months, both fibre and particle concentrations in Warnemuende remain comparable to other locations along the Rostock coast. The large fibre concentration is only seen in transparent fibres, such that we cannot be certain that these fibres do not have a natural origin at this point. A more thorough spectroscopic analysis would be needed to confirm these fibres as synthetic.

The comparison with studies where microplastics were identified with similar means confirms harbour locations as major entry pathways for microplastics. It is surprising that sediment from the bottom of sea shelfs, such as the Helgoland and Belgian Continental Shelfs, also contains large concentrations of microplastics. This supports the assumption that sediments, including beach sediments, serve as sinks for microplastic particles, and implies that further, more extensive studies of the amount of microplastics in the marine environment are needed to quantify the level of contamination in the marine food web.

The complete results can be found in my Master thesis:

The detection of microplastics in beach sediments:
Extraction methods, biases, and results from samples along the German Baltic coast


Only a selected choice of the rapidly increasing number of microplastics publications is provided here, as referenced in the text above, yet the interested reader is refered to the numerous recent publications available online.

Claessens, M., De Meester, S., Van Landuyt, L., et al. 2011: Occurrence and distribution of microplastics in marine sediments along the Belgian coast, Marine Pollution Bulletin 62, 2199-2204

Cole, M., Lindeque, P., Fileman, E., et al. 2013: Microplastic ingestion by zooplankton, Environtal Science & Technology 47, 6646-6655

Dekiff, J. H., Remy, D., Klasmeier, J., Fries, E. 2014: Occurrence and spatial distribution of microplastics in sediments from Norderney, Environmental Pollution 186, 248-256

Dubaish, F., Liebezeit, G. 2013: Suspended Microplastics and Black Carbon Particles in the Jade System, Southern North Sea, Water Air Soil Pollution 224, 1352, 1-8

Fossi, M. C., Panti, C., Guerranti, C., et al. 2012: Are baleen whales exposed to the threat of microplastics? A case study of the Mediterranean fin whale (Balaenoptera physalus), Marine Pollution Bulletin 64, 2374-2379

Fossi, M. C., Coppola, D., Baini, M., et al. 2014: Large filter feeding marine organisms as indicators of microplastic in the pelagic environment: the case studies of the Mediterranean basking shark (Cetorhinus maximus) and fin whale (Balaenoptera physalus), Marine Environmental Research, 100, 17-24

Jambeck, J. R., Geyer, R., Wilcox, C., et al. 2015: Marine pollution. Plastic waste inputs from land into the ocean, Nature, 347, 768-771

Lorenz, C. 2014: Detection of microplastics in marine sediments of the German Coast via FT-IR spectroscopy, Master thesis, Mathematisch-Naturwissenschaftliche Fakultaet der Universitaet Rostock

Mathalon, A., Hill, P. 2014: Microplastic fibers in the intertidal ecosystem surrounding Halifax Harbor, Nova Scotia, Marine Pollution Bulletin 81, 69–79

Noren, F. 2008: Small plastic particles in Coastal Swedish waters, N-research and KIMO Sweden

Thompson, R. C., Olsen, Y., Mitchell, R. P., Davis, A., et al. 2004: Lost at Sea: Where Is All the Plastic? Science 304, 838

Van Cauwenberghe, L., Janssen, C. R. 2014: Microplastics in bivalves cultured for human consumption, Environmental Pollution 193, 65-70

von Moos, N., Burkhardt-Holm, P, Koehler, A. 2012: Uptake and effects of microplastics on cells and tissue of the blue mussel Mytilus edulis L. after an experimental exposure, Environmental Science & Technology 46, 11327-11335