11:00 AM - 1:00 PM
[MIS19-P03] Distribution and accumulation process of microplastics in the eastern coastal area of Shimane Peninsula
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.
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.