Microplastics accumulation in surface waters of the Wadden Sea: The role of biogenic enrichment in marine foam

, Hernando Morales Victor, Ndhlovu Rachel T., Mol Anne, Vaksmaa Annika, Niemann Helge.

Plastic pollution is a worldwide environmental problem with adverse consequences to marine life and human health. One of the characteristics that makes plastic useful and highly demanded compared with other materials is its lightness. Due to the low density, many plastics float making rivers a perfect route for millions of tons of plastic to seep into the ocean every year. However, a discrepancy exists between those vast quantities and the amounts of floating plastics traced back at the sea surface ( 1% of all plastic debris in the environment). This mismatch could be the result because a substantial fraction might have sunk to the ocean floor or deposited along the coast. Besides, the distribution of floating plastic is heterogeneous, which complicates abundance estimations. We have investigated aggregation of floating plastics in marine foam in Dutch waters as a result of Langmuir and other convergent currents. These currents are visible at the sea surface as streaks/lines of marine foam, which is mainly derived from extracellular polymers and other biogenic products. Foam and marine snow can influence the fate of macro- and microplastics in the ocean through emulsification, aggregation, biofilm formation, and/or sedimentation. However, studies on microplastics in these biogenic motorways are limited. We sampled a total of 12 parallel surface trawl transects at two locations of the Wadden Sea, inside and just adjacent but outside of the foam. Preliminary results of visible plastics on the supernatants showed microplastic abundances ranging from 0 to 0.140 pieces per m2. We found a significant difference between transects with ¿ 25 fold higher concentrations of microplastic particles in samples recovered from the foam. Our results show the need for an integrated effort in order to understand the effect of localized microplastic accumulation through currents and entrapment in foam on microplastics abundance and distribution in our oceans.

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