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Depth-stratified microplastic pollution in the Arabian Sea: Abundance, composition, and transport mechanisms
Summary
Scientists sampling the Arabian Sea found tiny plastic bits (microplastics) concentrated heavily near the surface, with much less as you go deeper — mostly tiny fibers from clothing and fishing gear, plus fragments from packaging. Since surface waters are where much of our seafood feeds and where fishing occurs, this matters because these plastics can work their way into the marine food chain and, ultimately, onto our plates.
Microplastics (MPs) have emerged as pervasive contaminants in marine ecosystems; however, their vertical distribution within the Arabian Sea water column remains poorly understood. This study investigated the abundance, characteristics, polymer composition, and vertical transport of MPs across surface (0-10 m), middle (10-25 m), and bottom (25-40 m) waters at six offshore stations extending from Kerala to Gujarat along the eastern Arabian Sea. A total of 2758 MPs were identified from all sampling stations, Surface waters exhibited the highest standardized MP abundance among the investigated depth layers (2452 MPs m), followed by middle (244 MPs m) and bottom layers (62 MPs m), indicating strong vertical stratification. Karnataka recorded the greatest MPs abundance (577 MPs m), whereas Gujarat exhibited the lowest concentration (235 MPs m). Fibres were the dominant morphotype (54.7%), followed by fragments, sheets, and foam particles, while particles <2 mm constituted the major size fraction across all depths. Blue and red MPs predominated throughout the study area. ATR-FTIR analysis identified LDPE (13.3%), PET (8.3%), PS (8.3%), PA (6.7%), and PP (6.7%) as the major polymers, reflecting inputs from fishing activities, packaging materials, synthetic textiles, and maritime operations. Multivariate analyses (ANOVA, PCA, HCA, correlation, and NMDS) revealed significant station-specific and depth-dependent variability, confirming selective vertical redistribution through biofouling, aggregation, and density-driven settling. These findings demonstrate that the Arabian Sea functions as an active transport and storage continuum for MPs and highlight the necessity of incorporating vertical water-column assessments into regional marine pollution monitoring and ecological risk evaluation frameworks.