What drives the alongshore distribution of anthropogenic microparticles in sea coastal zones?

The distribution of anthropogenic microparticles (AMPs) in marine sediments is still not well understood and characterized as chaotic, being influenced by too many factors, such as hydrodynamics, sediment characteristics, anthropogenic pressures, and AMPs properties. This study analyzes the contamination of bottom sediments along a 12-km longshore transect following the 25-m isobath in the southeastern Baltic Sea with AMPs (0.3-5 mm; fibers included; ZnCl₂ used for separation; μ-Raman used for spectroscopic verification). A total of 55 samples from 19 stations were processed, revealing a mean blank corrected AMPs abundance of 271 ± 214 items/kg dry weight (737 ± 598 items/kgDW without correction, more than 97 % fibers). Alongside the AMPs abundance, size and shape distributions, the sediment grain size distribution, coarseness, and sorting were analyzed. Under similar environmental conditions along the transect, the strongest and statistically significant correlation was found between the abundance of fibers and sediment grain size in the range of 50-100 μm. Although fiber content increased with decreasing sediment grain size, no correlation was found with the percentage of the clay-silt fraction (<63 μm). In light of experimental studies of AMPs and sediment particle hydrodynamics, a possible scenario of AMPs hotspot formation was discussed.