09:15 〜 09:30
[MIS02-02] 日本南東沿岸域の表層海水におけるマイクロプラスチック濃度、カルボニルインデックス、および生態リスク
キーワード：マイクロプラスチック、海洋汚染、生態リスクアセスメント、赤外分光法、カルボニルインデックス
Microplastic are usually defined as plastic particles smaller than 5 mm, and it be further categorized into small microplastic (SMP, <350 μm) and large microplastic (LMP, >350 μm). Microplastic pollution in marine environments has become an increasing environmental concern due to its potential adverse effects on ecosystems and human health. However, there is limited data on pollution levels across various ocean areas. While recent studies have investigated microplastic pollution in various marine regions, they often focus on isolated locations, and a systematic assessment of microplastic contamination along Japan's southeastern coastal regions is lacking. Additionally, most research has primarily examined LMPs, leaving SMPs rarely understudied. Therefore, this study aims to address these gaps by evaluating microplastic pollution along the southeastern coast of Japan. The main objectives are to (1) measure microplastic concentrations, (2) analyze the spatial distribution, polymer type, particle size distribution, and degradation of microplastics, and (3) assess the ecological risks associated with microplastic pollution in this region.
In this study, surface seawater samples were collected from seven stations along the southeastern coast of Japan, ranging from the Tokai region to the south of Okinawa. A neuston net (350 μm mesh size) was used for LMP sampling, while a double neuston net (30 μm outer mesh and 100 μm inner mesh) was used for SMP sampling. The collected samples underwent chemical treatment and density separation before analysis. Potential LMPs were identified using attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR), while SMPs samples were analyzed with micro-FTIR. Polymer types were determined using the KnowItAll database, with a hit quality index (HQI) greater than 60.
LMP concentrations ranged from 0.014 to 0.094 pieces/m³ at most stations, except for a site near the Bungo Channel mouth, where concentrations reached 0.723 pieces/m³. Polystyrene (PS) foam was the most prevalent polymer near the eastern coast of Kyushu, with its presence decreasing both northward and southward, suggesting that the Seto Inland Sea may be a potential source of PS foam. Surface SMP concentrations ranged from 92 to 3,306 pieces/m³, with significantly higher concentrations near the Tokai region, where polyethylene (PE) was increasingly dominant. Particle size did not exhibit a clear spatial trend among stations, but further analysis showed that the particle size distribution followed exponential pattern. The carbonyl index (CI) values of PE LMPs increased from the southern region toward the north, suggesting the northward transport of microplastics from upstream southern regions. In contrast, CI values of PE SMPs initially increased but then declined after passing through the Bungo Channel and Kii Channel, indicating that the Seto Inland Sea is likely a source of microplastics, particularly PE. Ecological risk assessments indicated very high risks near major islands and densely populated regions, while remote areas exhibited lower risks. Further analysis showed that risk estimates were significantly affected by mesh selectivity, with variations of up to 100-fold at the same location depending on the mesh size used, suggesting that the current framework is not ideal for risk assessment of microplastics.
This study provides a comprehensive understanding of the abundance, distribution, and characteristics of microplastics in the southeastern coastal regions of Japan in the northwest Pacific. These findings could contribute to a better understanding of the environmental fate of microplastics. Additionally, the study highlights the significant influence of mesh selectivity on ecological risk estimates, emphasizing the need for standardized sampling protocols in microplastic research.
In this study, surface seawater samples were collected from seven stations along the southeastern coast of Japan, ranging from the Tokai region to the south of Okinawa. A neuston net (350 μm mesh size) was used for LMP sampling, while a double neuston net (30 μm outer mesh and 100 μm inner mesh) was used for SMP sampling. The collected samples underwent chemical treatment and density separation before analysis. Potential LMPs were identified using attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR), while SMPs samples were analyzed with micro-FTIR. Polymer types were determined using the KnowItAll database, with a hit quality index (HQI) greater than 60.
LMP concentrations ranged from 0.014 to 0.094 pieces/m³ at most stations, except for a site near the Bungo Channel mouth, where concentrations reached 0.723 pieces/m³. Polystyrene (PS) foam was the most prevalent polymer near the eastern coast of Kyushu, with its presence decreasing both northward and southward, suggesting that the Seto Inland Sea may be a potential source of PS foam. Surface SMP concentrations ranged from 92 to 3,306 pieces/m³, with significantly higher concentrations near the Tokai region, where polyethylene (PE) was increasingly dominant. Particle size did not exhibit a clear spatial trend among stations, but further analysis showed that the particle size distribution followed exponential pattern. The carbonyl index (CI) values of PE LMPs increased from the southern region toward the north, suggesting the northward transport of microplastics from upstream southern regions. In contrast, CI values of PE SMPs initially increased but then declined after passing through the Bungo Channel and Kii Channel, indicating that the Seto Inland Sea is likely a source of microplastics, particularly PE. Ecological risk assessments indicated very high risks near major islands and densely populated regions, while remote areas exhibited lower risks. Further analysis showed that risk estimates were significantly affected by mesh selectivity, with variations of up to 100-fold at the same location depending on the mesh size used, suggesting that the current framework is not ideal for risk assessment of microplastics.
This study provides a comprehensive understanding of the abundance, distribution, and characteristics of microplastics in the southeastern coastal regions of Japan in the northwest Pacific. These findings could contribute to a better understanding of the environmental fate of microplastics. Additionally, the study highlights the significant influence of mesh selectivity on ecological risk estimates, emphasizing the need for standardized sampling protocols in microplastic research.