MiCROPLASTICS

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The microplastic concentration over the entire race route from the Baltic Sea to the Mediterranean sea (see map above) ranged from 21 to 433 particles per m³, with an average concentration of 138 particles per m³.

It is important to note that these concentrations, including minimum/maximum, will vary over time, due to changing ocean circulation. In fact, one of the maximum concentrations measured in the Mediterranean Sea (424 particles/m³, sampled by AkzoNobel Ocean Racing boat during May) was from a site where a later sample collected by Ambersail-2 boat in a similar area yielded a much smaller concentration (29 particles/m³). The AkzoNobel Ocean Racing May sample was collected closer to shore so proximity to human plastic sources could be a factor. The time of the season may also have influenced the measurements as microplastics are known to have the ability to ‘stick’ to phytoplankton and sink to the seabed when phytoplankton blooms die and fall to deeper water¹. As the time between samples may have coincided with the end of the summer phytoplankton bloom, this could potentially by a factor, the second sample being post-bloom after microplastics were drawn down to deeper waters.

The maximum average microplastic concentrations were recorded in the Baltic Sea and these were about twice as high as the averages in the Atlantic Ocean and Mediterranean Sea regions. Individual samples with largest microplastic concentration values were found both in the Baltic Sea and in the Mediterranean Sea. The samples with lowest concentration were collected off the coast of Brittany and in Gibraltar Strait.

¹ Long, M., Moriceau, B., Gallinari, M., Lambert, C., Huvet, A., Raffray, J. & Soudant, P. (2015) Interactions between microplastics and phytoplankton aggregates: Impact on their respective fates. Marine Chemistry. 175: 39–46. DOI:10.1016/j.marchem.2 015.04.003

The analysis methods employed ² (and see summary below) allowed separation of microplastic fibres and fragments which is a new feature compared to analysis of microplastic samples done during the 2017-18 edition of The Ocean Race ³.

Microplastic fibres originate from the manufacturing, washing and wearing of clothes made of synthetic fibers, fragmented fishing gear or car tyres that lose very small thread-like plastic fibers in the environment. The microfibres have small diameter ~10μm or less, with length 0.5-2.0 cm. In contrast, microplastic fragments come from the degradation of larger plastic pieces and have sizes in the range 1μm-5mm.

Plastic microfibre is a relatively new area of study that is receiving increasing attention as it is expected to be the major source of plastics throughout the world's oceans. It is estimated that up to 13 million tonnes of coastal synthetic fabric waste are entering the ocean each year, out of which 2.5 million tonnes enter through adjoining rivers⁴. Other plastic sources includes waste from coastal populations, fisheries, aquaculture and shipping. Furthermore, microplastic fibres are the most frequent microplastic type ingested by marine animals⁵.

The new methodology also characterised microplastic particle (fibre or fragment) colors (see graphic below). There is evidence that some organisms ingest some colors of microplastics preferentially (e.g. black) to others (e.g blue, clear, yellow) ^6,7,8. Fibres may also be consumed preferentially to fragments⁹, although this is not always the case⁸.

On average, collected microplastic samples included 83% fibers and 17% fragments. Three samples coming from the Atlantic Ocean and Baltic Sea included only fibres (100%). The minimum amount of fibres measured was 48%, in the Mediterranean Sea. The mean fraction of fibres to total particles decreased only slightly moving from the Baltic Sea, to Atlantic Ocean to Mediterranean Sea, with fractions 87%, 80 %, 73% .

The collected samples were analysed to produce a count of fragment and fibre particles per cubic meter of surface seawater, i.e. microplastic concentration. The 'total' microplastic concentration is the sum of micro fragment and fibre concentrations.

²Beck, A.J., M. Kaandorp, T. Hamm, B. Bogner, M. Lenz, E. Van Sebille, E.P. Acterberg. Rapid shipboard measurement of net-collected marine microplastics using near-infrared hyperspectral imaging, in prep.

³Tanhua, T., Gutekunst, S.B., & Biastoch, A. (2020). A near-synoptic survey of ocean microplastic concentration along an around-the-world sailing race. PLoS ONE, 15.

⁴Mishra, S., Rath, C.C., & Das, A. (2019). Marine microfiber pollution: A review on present status and future challenges. Marine pollution bulletin, 140, 188-197 .

⁵Rebelein, A., Int-Veen, I., Kammann, U., & Scharsack, J.P. (2021). Microplastic fibers - Underestimated threat to aquatic organisms? The Science of the total environment, 777, 146045 .

⁶Ory, N. C., Gallardo, C., Lenz, M., & Thiel, M. (2018). Capture, swallowing, and egestion of microplastics by a planktivorous juvenile fish. Environmental pollution, 240, 566-573.

⁷Lopes, C., Raimundo, J., Caetano, M., & Garrido, S. (2020). Microplastic ingestion and diet composition of planktivorous fish. Limnology and Oceanography Letters, 5(1), 103-112.

⁸Xiong, X., Tu, Y., Chen, X., Jiang, X., Shi, H., Wu, C., & Elser, J. J. (2019). Ingestion and egestion of polyethylene microplastics by goldfish (Carassius auratus): influence of color and morphological features. Heliyon, 5(12).

⁹Peters, C. A., Thomas, P. A., Rieper, K. B., & Bratton, S. P. (2017). Foraging preferences influence microplastic ingestion by six marine fish species from the Texas Gulf Coast. Marine pollution bulletin, 124(1), 82-88.

When combined with other in-situ measurements of microplastics from other sampling campaigns, the results represent valuable input to computer models to help estimate the distribution of microplastic in the ocean, as well as their variability over time over large spatial areas.

For example, this was done in the Mediterranean Sea by a team of scientists from the University of Utrecht⁹ . Using numerical model simulations and in-situ microplastic measurements, they were able to evaluate a plastic mass budget by quantifying possible plastic sources (i.e. where does plastic come from) and sinks, notably how much end up on the coasts, and how much sink to the seabed. Their method can also provide insights on the relative importances on the likely plastic sources such as mismanaged plastic waste from coastal populations, riverine input from inland population, or input due to fisheries activities. For their study period (2015), they estimated a total plastic input to the Mediterranean Sea in the range 2100-3400 tonnes out of which 1200-1900 tonnes beached (49-63%), 900-1500 tonnes sunk to the seabed (37-51%) and 170-420 tonnes remain afloat.

⁹Kaandorp, M.L., Dijkstra, H.A., & van Sebille, E. (2020). Closing the Mediterranean Marine Floating Plastic Mass Budget: Inverse Modeling of Sources and Sinks. Environmental Science & Technology, 54, 11980 - 11989.

During The Ocean Race Europe, the AkzoNobel Ocean Racing and Ambersail-2 boats sampled microplastics using underway sampling systems installed onboard. The system pumps seawater through an inlet on the ship hull and into a series of filters which are sent to the laboratory for ex-situ analysis at each race stopover. The water inlet is about 3 metres below the sea surface and therefore collects seawater from the surface mixed layer. This contrasts with other methods like Manta nets that collect microplastic floating on the surface.

A total of 36 samples were collected along the boat tracks. The average time between filter change was ~12h (min 2h, max 22h) and the coordinates of the start and end points were recorded. The volume for each sample averaged 0.37 m³. Two filters were used with mesh sizes of 100 and 500 μm. Each filter was stored in a mylar Ziploc bag and placed into the system with a clamp to avoid contamination. Once used, the filter was removed with the same clamp and placed back into its mylar Ziploc bag. Once at ports, filters were sent to GEOMAR Helmholtz Centre for Ocean Research, Kiel laboratory for analysis.

The samples collected during The Ocean Race Europe provided an opportunity to experiment with a new laboratory analysis technique².

In a laboratory under filtered air each filter was transferred to a glass beaker and the inside of the bag rinsed into the beaker with ultrapure water. The filter was sonicated in an ultrasonic bath for 15 minutes to remove particles, and the filter removed from the beaker and rinsed. The remaining suspension was then filtered onto a glass-fibre filter under gentle vacuum, and filters air-dried and stored in glass petri dishes. Plastic fragments and fibres were identified visually under magnification by personnel trained on reference particles down to 20 µm in size. Plastic items were transferred to glass mounting slides for imaging, size measurement, and polymer identification by near-infrared hyperspectral imaging . This method has a practical size detection limit of about 100 µm, but reliable measurement is limited by the narrowest particle dimension. Unfortunately, the particles found in the current study were too small to give clearly identifiable spectra for polymer identification. Work is ongoing to improve detection limits for small particles. Note the presented analysis focuses on the 500 µm filter data.