Microplastic contamination in pelagic and coastal fish from Malaysian waters: Tissue-specific distribution, polymer characteristics, and environmental risk indicators

This study quantified the abundance, tissue-specific distribution, polymer composition, and preliminary contamination screening of microplastics (MPs) in two commercially important pelagic fish species from Malaysian coastal waters, Megalaspis cordyla and Katsuwonus pelamis (n = 60). Microplastics were isolated from gill, digestive tract, and muscle tissues using hydrogen peroxide (H₂O₂) digestion, followed by stereomicroscopic inspection and polymer confirmation using ATR-FTIR spectroscopy. Microplastics were detected in 93.3% of M. cordyla and 86.7% of K. pelamis. While total burdens per individual were comparable between species, tissue-normalized concentrations (particles/g wet weight) revealed significantly higher digestive tract and gill loads in M. cordyla. Particles were predominantly fragments within the 0.1-0.5 mm size range. Polyethylene (PE) and polypropylene (PP) were the dominant polymer types in both species. To provide a comparative ecological perspective, two index-based screening tools were applied. The Polymer Hazard Index (PHI) indicated low intrinsic hazard potential based on polymer identity alone, whereas tissue-derived Contamination Factors (CF) revealed substantial recent ingestion pressure in digestive tracts. However, organism-level Pollution Load Index (PLI) values were moderated by negligible muscle concentrations, underscoring the influence of tissue weighting in composite indices. Overall, these findings indicate pervasive environmental exposure to microplastics in Malaysian pelagic fisheries, while direct physical exposure through muscle consumption appears limited under the particle size range assessed. The study provides baseline data for regional biomonitoring and highlights the need for integrated environmental sampling and improved plastic waste management strategies.