First evidence of microplastic contamination in surface waters of Loktak Lake, a Ramsar site in the Eastern Himalayas

Microplastic (MP) pollution in freshwater ecosystems is an emerging environmental threat yet remains poorly documented in ecologically sensitive wetlands. Here, we present the first integrated assessment of MP occurrence, distribution, polymer composition, and associated risks in the surface waters of Loktak Lake (Manipur, India), a globally unique floating lake system and Ramsar site. Surface-water samples were collected during the pre-monsoon season (March 2024) from the 0-20 cm surface layer from 13 geospatially distributed sites. MP abundance exhibited pronounced spatial heterogeneity, ranging from 8 to 82 particles L⁻¹ (mean 47 ± 23.8 particles L⁻¹). MP hotspots are concentrated near densely inhabited islands, floating hutments, market-associated zones, and active fishing areas. Spatial concentration variation was statistically supported through a strong monotonic association between MP abundance and the anthropogenic intensity. Size profiling showed a dominance of small particles, with particles < 2000 μm accounting for 91.38% of total MPs, highlighting high bioavailability potential. Predominant MP morphotypes included fibers and fragments. Polymer identification confirmed the presence of common consumer and activity linked polymers, including polypropylene (PP), polyethylene terephthalate (PET), polyamide (PA), and polyvinyl chloride (PVC). EDX analysis revealed associated trace metals including Pb, Ru, and Pt, indicating potential polymer-metal interactions. An environmental risk evaluation integrating indices indicated elevated ecological concern in high-activity zones. The estimated human health risks (non-carcinogenic and carcinogenic) via ingestion remained within acceptable thresholds under current exposure assumptions. However, the presence of carcinogenic polymers such as PVC raises significant concern. This study provides a critical baseline to guide monitoring, wetland management, and targeted source-control interventions in Ramsar and high-value freshwater ecosystems.