Microplastic pollution in Greek seas: Abundance, spatio-temporal dynamics, potential sources and post-storm amplification

Microplastic (MP) pollution represents an increasing threat to coastal and marine ecosystems, yet data from Greek waters remain scarce. This study provides a comprehensive assessment of MP abundance, spatial distribution, polymer composition, and seasonal variability in surface waters and sediments collected from 27 coastal sites in Greece between 2021 and 2024. Sampling was combined with Fourier – Transform Infrared (FT-IR) spectroscopy polymer identification and satellite-derived Suspended Particulate Matter (SPM) data, available for a subset of sites, to explore hydrodynamic influences on MP distribution and the effects of extreme events. The impact of Storm Daniel on the Pagasitikos Gulf was particularly notable, with a sharp and sustained increase in both SPM and MP concentrations persisting for over a year following coastal flooding. Seasonal analysis showed higher MP levels during winter and early spring, coinciding with elevated SPM and with periods that are climatologically associated with increased precipitation and runoff in Greece. Polymer analysis indicated that polyolefins (PE and PP) comprised approximately half of the detected MPs in both matrices, followed by PS in sediments and cellulose and PET in seawater. Morphologically, fragments and films were the most common MP types, particularly in highly impacted locations. MP concentrations exhibited strong spatial variability, ranging from 0 to 240.8 items/m 2 in sediments and 0.0008 to 0.1637 items/m 3 in surface waters. Overall, the results indicate that storm-driven runoff and hydrodynamic conditions can play an important role in mobilising MPs from terrestrial sources to coastal environments, particularly in semi-enclosed gulfs. This study provides new evidence linking extreme weather events, SPM dynamics, and MP transport in parts of the Greek coastal environment, offering insights for pollution monitoring and management strategies.