Comprehensive Analysis of Microplastic Abundance in Macrophytes, Macrophyte-Associated Sediments, and Water in Tropical Coastal Lagoons in Sri Lanka

The prevalence and fate of microplastics in macrophytes are insufficiently understood, and data on the abundance of microplastic (MP) accumulation in macrophyte ecosystems are urgently needed to fill this knowledge gap. The main objectives of this study were to quantify and characterize the microplastics that accumulate in macrophytes, associated sediments, and water in Negombo Lagoon, Sri Lanka. The investigation was conducted with specialized sampling and extraction techniques. Microplastics were detected by the fluorescence tagging of polymers using Nile red, and polymer identification was conducted by ATR-µFTIR and ATR-FTIR. This study revealed variations in microplastic abundance across different macrophyte species. Gracilaria sp. had a higher abundance of 9 ± 3 items g−1 wet weight, followed by Chaetomorpha sp. at 8 ± 3 items g−1 wet weight and Halodule pinifolia at 6 ± 1 items g−1 wet weight. The root surfaces of these species had slightly similar levels of abundance. Both blue and transparent microplastics were predominant. Fragments (>47%) were found at a higher percentage in macrophyte samples, but high fiber contents (>60%) were found in associated sediment and water samples. Nevertheless, macrophyte samples contained a higher percentage of fragments in the size range of 50–150 μm. This comprehensive study contributes to expanding our awareness regarding the influence of microplastic pollution on macrophyte ecosystems.