Seagrass beds reveal high abundance of microplastic in sediments: A case study in the Baltic Sea

Microplastic (MPL) contamination in the marine environment is extensively studied yet little is known about the extent of MPL abundance in seagrass beds. The aim of this study was to evaluate MPL accumulation in coastal seagrass (Zostera marina) beds in the Baltic Sea, Estonia. Surface water was sampled by pumping using 40 μm plankton net, and sediments by trowel. MPL was extracted with NaCl, identified by microscopy and ATR-FTIR on selected samples. Surface water in the seagrass beds had 0.04–1.2 (median 0.14) MPL/L, similar to other areas of the Baltic Sea. Sediments had 0–1817 (median 208) MPL/kg (dwt), much higher than previously recorded from adjacent unvegetated and offshore sediments, thereby suggesting a strong ability of the sediments in seagrass beds to retain MPL. Of identified MPL, blue fibres were dominant in both the sampled media. Sediment characterization showed a correlation between MPL counts with poorly sorted sediments. [Display omitted] •First microplastic abundance study in seagrass beds in the Baltic Sea•Study revealed high abundance of microplastic in seagrass beds•Blue fibres were the prevalent microplastic in both water and sediments.•More poorly sorted sediments had the highest microplastic concentrations.•Study highlights heterogeneity of microplastic abundance within sediment samples and microplastic counts.