Large prevalence of cellulosic fibers in the first-year sea ice from Amur Bay, Sea of Japan

The contamination of sea ice by microplastics (MPs) and microfibers (MFs) is still underexplored. In this study, we report the abundance, chemical composition, and vertical distribution of MPs and MFs in the seasonal sea ice of Amur Bay (Sea of Japan, Russia). More specifically, three ice cores (38-53 cm long) were manually extracted, sectioned into ∼5 cm layers, melted, and filtered without chemical pretreatment and then submitted to μFTIR analysis. A total of 29 filters, corresponding to ∼24.5 kg of sea ice, were analyzed. Overall, 6026 anthropogenic items in the 25-5000 μm size range were identified, yielding a bulk mean of 4716 ± 2509 items/L. Among them, 94.7% were fibers, 4.1% fragments, and 1.2% films. Particles between 0.3 and 5 mm represented over 80% of the total, while smaller particles were less abundant. Notably, 90% of fibers were cellulose-based. MPs averaged 685 ± 550 items/L and consisted mainly of polyester (47%), acrylic (25%), polyethylene (4%), and polystyrene (3%). Core T15-K4 exhibited significant stratification, with fibers concentrated in the middle layers, whereas T13-K1 and T15-K2 showed no significant vertical variation. These findings indicate that first-year sea ice functions as a temporary sink for anthropogenic particulate pollutants. The strong predominance of cellulosic MFs underscores the need to include natural and semi-synthetic fibers in future monitoring efforts.