Japan Geoscience Union Meeting 2022

Presentation information

[J] Poster

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS19] Ocean Plastics, an earth science perspective

Mon. May 30, 2022 11:00 AM - 1:00 PM Online Poster Zoom Room (35) (Ch.35)

convener:Atsuhiko Isobe(Kyushu University), convener:Kiichiro Kawamura(Yamaguchi University), Yusuke Okazaki(Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University), convener:Masashi Tsuchiya(Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology), Chairperson:Atsuhiko Isobe(Kyushu University)

11:00 AM - 1:00 PM

[MIS19-P03] Distribution and accumulation process of microplastics in the eastern coastal area of Shimane Peninsula

*Akira Tsujimoto1, Kana Nishikohri1, Masashi Tsuchiya2, Hidetaka Nomaki3, Misako Matsuba4 (1.Faculty of Education, Shimane University, 2.Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 3.Institute for Extra-cutting-edge Science and Technology Avant-garde Research, Japan Agency for Marine-Earth Science and Technology, 4.Biodiversity Division, National Institute for Environmental Studies)

Keywords:Microplastics, Shimane Peninsula

In the coastal area of the Shimane Peninsula, a large amount of drifted litter including plastics has been observed due to the influence of the Tsushima Current and monsoon. It is important to investigate the distribution of microplastics (MPs) and their accumulation, fragmentation processes in terms of their biological effects. Shimane Peninsula is facing to the Japan Sea and have complex geography with different directions of beaches, making complicated drifting processes at each beach.
In this study, we investigated four beaches in the eastern part of the Shimane Peninsula: Konami, a westward-facing beach; Chikumi, a northeastward-facing beach; Kitaura, a northward-facing beach; and Kasaura, a southward-facing beach. Except for Kasaura, the other three beaches are located behind villages and are used as swimming beaches in summer. In May 2021, we collected sediment samples at a depth of 30 cm and at the shoreline during high tide, and in October, we collected sediment samples at the shoreline during high tide. In the laboratory, we analyzed MPs of 300 µm-4.75 mm in size from the sediment samples. Shape classification, color classification, and longitudinal measurements were performed, and Raman spectroscopy was used to discriminate plastic materials.
The results of the May survey showed that several MPs were extracted from the shoreline during high tide, while almost none were extracted from the sediment at 30 cm water depth. This may be due to the plastic particles being fragmented on the beach and deposited near the shoreline, while the fragmented particles are transported offshore during high tide.
The results of the October survey showed that foamed polystyrene was the most common material, accounting for 84 to 96% of the MPs at all beaches. There was no significant difference in the material and shape of the MPs depending on the beach, suggesting that the MPs drifting on the Shimane Peninsula originated mainly from currents rather than regional debris. On the other hand, the number of MPs per 1 kg of sand ranged from 967 to 5461, and the amount and size of MPs was different depending on the beach. This is probably due to differences in the drifting and refining processes caused by differences in the relative angles of seawater flow direction and wind direction depending on the orientation of the beach.