Reconstruction of radioactivity and microplastic particles studying sedimentation/accumulation in the deep Lemnos basin, North Aegean Sea, Greece

The objective of this work is to study environmental changes and contamination during the last century in a semi-closed marine system, by performing measurements on the sediment which is the final recipient of discharged matter. Sediment cores were sampled with a box-corer and were analyzed using gamma-ray spectrometry for activity concentration measurements and density separation/microscopic inspection for microplastic particles (MP) determination. The sedimentation rate was determined using the vertical profiles of 210Pbex and the results were validated via 137Cs measurements. The activity concentration results do not raise any radiological concern. The sedimentation rate increased after 1995. The ratio of 226Ra/228Ra activity concentrations was less than unity demonstrating that accumulation/accretion process is the main mechanism that takes place in terms of sediment dynamics. The microplastic particles concentrations were measured and correlated with the increased water supply of the rivers flowing into the North Aegean, combined with the production of dense water masses. The sedimentation rate from 1995 to 2020 drastically increased due to extreme weather events (e.g., flooding effects as an impact of climate change). The accumulation/accretion process in the semi-closed system is validated. Flooding periods and deep formation events were utilized to interpret the distribution of microplastic particles.