Assessment of Buoyant Plastics in the Andaman and Nicobar Archipelago: Seasonal Dynamics, Source Attribution, Polymer Characterization, and Adverse Impacts

Abstract

Plastic pollution presents a growing threat to marine ecosystems, with significant impacts on biodiversity and trophic interactions. This study investigated the distribution, abundance, and ecological implications of buoyant plastics in the offshore waters of the Andaman and Nicobar Archipelago over a 12-month period. A total of 178 ship-based visual surveys were conducted, covering 6898 km. The average annual abundance of buoyant plastics was 78.94 ± 14 items km⁻2, with Flexible Packaging Plastics (FPP) and Miscellaneous Plastics (MP) comprising 43.4% and 44.3% of the total plastics, respectively. Seasonal trends revealed the highest abundances during the pre-monsoon period (101.41 ± 20 items km⁻2), likely driven by increased human activities such as fishing and tourism, while the lowest abundances were observed during the winter monsoon (59.36 ± 19 items km⁻2). Notable monthly peaks occurred in January, April, and October. A clear depth gradient was evident, with higher plastic abundances in shallower waters (0–1000 m; 93.48 ± 34 items km⁻2) and reduced concentrations at greater depths (3001–4000 m; 58.39 ± 19 items km⁻2). Plastic ingestion was assessed in 248 large pelagic fish from 13 species. Bigeye Thresher Sharks (42.86%) and Indo-Pacific Blue Marlins (40%) showed the highest ingestion rates. Ingested buoyant plastics ranged up to 78 cm2 in size and predominantly consisted of common polymers such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). These insights reinforce the urgent need for mitigation strategies to address the ecological risks associated with buoyant plastics. © University of Tehran 2025.