Vertical profiles of microplastics in coastal sediments of Panjang Island, Java Sea

The proliferation of plastic pollution has led to the widespread accumulation of microplastics (MPs) in marine ecosystems. While surface sediment contamination is relatively well studied, knowledge of vertical MP distribution within sediment columns remains limited. This study examines the abundance, vertical distribution, and characteristics of MPs in subtidal and intertidal sediments of Panjang Island, Java Sea. Fifteen shallow (10 cm) and three deep (∼100 cm) sediment cores were analyzed for MP abundance, morphology, size, color, and polymer using microscopy and ATR-FTIR. MPs were detected in all cores, with an average concentration of 0.49 ± 0.28 MPs g⁻¹ in surface sediments. The highest surface concentration (2.08 ± 0.22 MPs g⁻¹) occurred in the southwest, a sheltered site with greater anthropogenic influence, while the lowest (0.05 ± 0.07 MPs g⁻¹) was recorded in the northwest, a remote and less disturbed area. Fibers dominated particle types. White, black, and blue were the most common colors, and size distributions were skewed toward particles <1 mm. Polypropylene and polyethylene were the most frequent polymers, reflecting their widespread use and persistence. Vertical profiles revealed higher MP concentrations near the surface, indicating intensified inputs in recent decades. No MPs were detected below 70 cm, suggesting limited downward migration and marking the onset of contamination during the plastic era. This study also found MPs in deeper sediment layer, likely due to post-depositional processes such as bioturbation. These findings demonstrate that sediment cores serve as valuable archives of historical MP deposition, capturing both global production trends and local environmental influences, and provide a basis for targeted management strategies.