Anthropogenic Microparticles in Sea-Surface Microlayer in Osaka Bay, Japan

Area of Science:

• Environmental Science
• Marine Pollution
• Polymer Science

Background:

• Microplastics (MPs) are a growing concern in marine environments.
• Investigating MPs in the sea-surface microlayer (S-SML) and bulk water is crucial for understanding pollution levels.

Purpose of the Study:

• To assess the pollution level of MPs in Osaka Bay, Japan.
• To determine the abundance, distribution, and composition of MPs in S-SML and bulk water.
• To identify the primary sources and types of MPs.

Main Methods:

• Seawater samples collected from Osaka Bay (2021-2023) at various sites.
• MPs filtered into size ranges (10-53, 53-125, 125-500, >500 μm) and digested.
• Abundance assessed microscopically; polymer types identified using Fourier transform infrared spectrometry (FTIR).

Main Results:

• Average MP abundance: 903 ± 921 items/kg in S-SML vs. 55.9 ± 40.4 items/kg in bulk water.
• Highest MP concentrations found along ship navigation routes.
• Smallest MPs (10-53 μm) constituted 81.2% (S-SML) and 62.2% (bulk water).
• Polymethyl methacrylate (PMMA) was the dominant MP type (95.1% in S-SML, 45.6% in bulk water), especially in the smallest size fraction.

Conclusions:

• Osaka Bay exhibits significant microplastic pollution, particularly in the sea-surface microlayer.
• Marine paints, specifically antifouling paint particles (APPs), are a likely major source of PMMA.
• Microplastic pollution from ship vessels requires focused attention and mitigation strategies.