Origins and ecological risk of atmospheric microplastics at a remote background site in Japan

Atmospheric microplastics (AMPs) deposition was monitored over a 10-month period (May 2022 - Feb. 2023) at the Kanazawa University Wajima Air Monitoring Station (KUWAMS), a remote background site in Wajima, Japan. AMPs deposition rates at KUWAMS ranged from 55 to 560 n/(m²·d), with 75 % of particles smaller than 50 μm. Fragments (96.4 %), fibers (1.7 %), beads (1.6 %), and films (0.2 %) were identified with fragments being the most common. Most AMPs were composed of polyamide (22.3 %) and polyethylene terephthalate (35.9 %), likely from packaging and automotive materials. Estimated AMPs possible transportation time and backward trajectory modeling, showed that higher AMPs deposition rates and compositional differences during summer (Jul. - Sep. 2022) and winter monsoon periods (Dec. 2022 - Feb. 2023), were driven by air masses from mainland Japan and continental Asia, respectively. Total annual AMPs deposition in Wajima (426 km²) was estimated to be 2.27 tons. Our preliminary potential ecological risk evaluation indicated that KUWAMS falls under Risk Level V, indicating an extreme ecological consequence and necessitating further investigation into AMPs pollution. This is the first study to demonstrate that background sites in East Asian monsoon region exhibited AMPs deposition and complexity. These findings highlight the necessity for increased attention to AMPs in background sites and provide a valuable reference for future research.